Mechanical practices. Mechanical control options can take advantage of the stinkwort root system, which is slow growing and initially relatively shallow. Plants may be controlled by hoeing or pulling. However, because stinkwort can cause dermatitis, it is important to wear appropriate protective clothing to minimize exposure to the irritating oils. Once in flower, stinkwort plants should be bagged and removed from the site to prevent seeds from maturing and dispersing after the plants have been cut and left on the soil surface. Mowing can provide partial control when conducted late in the season . However, buds remaining on branches below the level of the mower may regrow. Mowing a second time can give improved control, especially when conducted after the soil has dried out in mid- to late summer. In contrast, mowing too early, as is done on highways to reduce the threat of grass fires, will favor stinkwort by removing competing annuals while this weed is still small and lower than the mowing blades. Postemergence herbicides. Thus, in contrast to preemergence herbicides that are generally applied to larger areas before seeds germinate, post emergence applications can directly target known infestations visible to the applicator. However, the sticky oils on the foliage, especially on mature plants, make it difficult to control stinkwort with post emergence herbicides. To overcome this, it may be necessary to use ester formulations of post emergence phenoxy-type herbicides .

However, these compounds are more volatile compared to salt formulations , and some should not be applied when ambient temperatures will reach or exceed 80°F. In experiments we conducted for the post emergence control of stinkwort, we found that the salt formulation of triclopyr at 24-ounce acid equivalent per acre gave the most effective level of control following a post emergence application . Triclopyr is selective and relatively safe on grasses, but it must be used cautiously around vineyards, as grapevines are extremely sensitive to triclopyr drift. It is also important to note that control with post emergence herbicides is most effective when plants are young, actively growing and not exposed to stresses such as drought. For stinkwort, this is generally just before or at the time of bolting.Glyphosate at 1 quart product per acre also gave fairly good control, and anecdotal information from other land managers indicates that a rate of 2 quarts product per acre gives control similar to triclopyr at 2 quarts product per acre. Unfortunately, other herbicides, including aminopyralid and aminocyclopyrachlor , did not provide effective late-season postemergence control of stinkwort. As previously discussed, plants also partially recovered from late-season mowing. Pre- and early post emergence herbicides. Because stinkwort germinates throughout the rainy season, the most effective control options are likely to be broadleaf selective herbicides with both pre- and early post emergence activity, which can control both new germinants and young emerged seedlings. A fairly new group of foliar- and soil-active growth regulator herbicides have proven very effective in winter and spring applications for control of yellow starthistle and other members of the sunflower family . These herbicides have the ability to control both emerged young plants through foliar activity, as well as germinating seedlings through soil activity.

These chemicals include clopyralid , aminopyralid and aminocyclopyrachlor, and they are generally safe on grasses. In preliminary demonstrations, we found that winter applications of aminocyclopyrachlor and spring applications of Milestone VM+ showed the greatest potential for controlling stinkwort. Early-season application of glyphosate, however, controlled competing vegetation and so allowed late-germinating stinkwort to thrive. Thus, glyphosate is best used later in the season as a post emergence application. This ongoing research is building our understanding of the life cycle and basic biology of stinkwort, allowing us to make predictions of invasion potential that will help prioritize management activities. This work also lays a foundation for future investigation of specific management methods. If we expect to stop or slow the spread of this newly invasive plant in California, we must quickly develop effective management tools and an informed management approach.Communities and countries experiencing poverty, high unemployment, and economic reliance on tobacco growing are vulnerable to predatory tobacco industry behaviour. This analysis presents a cross-national survey of social disruption in tobacco farming to illustrate the association between tobacco companies and tobacco-related child labor, poverty and environmental destruction. The health risks of tobacco farming are beyond the scope of the study. Data on social disruption in tobacco farming was obtained through newspaper stories, published and unpublished reports, scholarly literature, documentary films, and tobacco industry publications such as annual reports and websites. The analysis shows that in all World Health Organization regions tobacco farming involves child labor and deforestation as well as tobacco industry behaviour promoting disruption in social and environmental life in tobacco farming communities. Tobacco companies generate huge externalities forcing farmers and consumers to pay the costs and concealing the actual cost of tobacco leaf and other tobacco products. Tobacco growing has detrimental effects on poverty and development. Developing countries that experienced an expansion of tobacco growing in the 1970s witness economically active people turning to tobacco growing and land transformed into tobacco farms, diverting valuable human and environmental resources. Tobacco jobs characterized by unfair contract arrangements, bonded labor, and child labor push vulnerable, primarily rural, populations deeper into economic disenfranchisement. Tobacco-related deforestation and pesticide poisoning contribute to the cycle of poverty and health insecurity of tobacco farmers. Poverty related to tobacco growing is compounded by rates of smoking of tobacco farmers that are higher than people who are not tobacco farmers, putting added pressure on weak health care systems in tobacco growing developing countries from the eventual appearance of tobacco-related death and disease. Tobacco farming is labor intensive. Each harvest requires 200 days of work per person per year, nine times as much work as in the production of beans, for example.

One tobacco farmer may tend up to 400,000 individual leaves in a nine month growing season. Since casual agricultural workers are nearly impossible to find, farmers are forced to use their families to help them cultivate and perform other physically demanding tasks in the fields. Tobacco farmers have little or not time and land to grow food or non-tobacco cash crops. Ogaya Bade, a tobacco farmer for more than 10 years in Kenya, vertical growing racks explained the difficulties of tobacco growing and its impact on food crops, when he said, “To get something out of this crop one has to dedicate all his time for the proper management of the crop, otherwise you will get nothing,” and experience perpetual famine, and have no time to produce food crops. In Kenya, 80% actually lose money from growing tobacco. In Malawi, where tobacco accounts for 70% of the country’s foreign earnings, people eat fried mice, corn husks, and poisonous plant roots to survive during frequent maize shortages while tobacco exports remain uninterrupted. Tobacco farmers sell their crop at auction or on a contract basis. A tobacco auction is a marketplace where buyers bid for the tobacco in open competition, in Malawi and Zimbabwe, for example. Under contract farming a tobacco farmer agrees to grow tobacco for a buyer who, in turn, provides seeds, pesticides and other inputs on loan, deducting the costs from earnings. Cigarette manufacturers such as British American Tobacco and leaf companies such as U.S.-based Universal Corporation and Alliance One International buy tobacco directly from farmers. Two emergent patterns exist in the global tobacco farming sector: the auction system is being replaced by the contract system; and global leaf companies operate farms and contract with farmers on companies’ farms in India and Brazil, for example. Tobacco leaf selling arrangements contribute to the poverty of tobacco farmers. Tobacco farmers require unpaid labor from wives and children to meet contract requirements. Global tobacco companies through direct contract arrangements with Mexican farmers make harsh demands on farmers while contractually exonerating themselves from responsibilities for tobacco farm working and living conditions. In Nigeria, BAT requires farmers to increasingly cover production and transportation costs, leaving farmers few choices such as a strike to express their grievances. Contract farming is linked with poverty in Uganda. Uganda is a world supplier of tobacco. Tobacco accounts for 3 percent of the country’s export earnings . In Uganda over 600,000 people out of a population of 25 million derive their livelihood from tobacco.23 22,000 tobacco farmers are contracted to supply tobacco directly to BAT in exchange for loans for inputs like seeds, fertilizer, and other supplies. The case of Angiepabo, a 24 year old tobacco farmer in Uganda shows the links between poverty and contract farming in Uganda. Angiepabo “sold 200 kilos of his crop to BAT. After paying the union dues and deduction of the BAT loans and offsetting the cost of the wood fuel he was left with approximately $1.00 to carry home. Maybe my daughter or son will one day win a BAT scholarship is the answer Angiepabo gives as to why he keeps growing tobacco” . In Kenya, BAT operates contracts with tobacco farmers. The number of farmers contracted by BAT in Kenya increased by 67% from 7,000 in 1972 to 11,000 in 1991, and by 36% from 1991 to 1993. As the number of tobacco farms increased in Kenya, the average per capita incomes decreased 67% from 1971 to 1991. In Migori, Kenya, where BAT is based, 52% of the population suffer from chronic or acute hunger and malnutrition. Food production in the major tobacco-growing areas has decreased as farmers have shifted from food crops to tobacco for BAT and other companies, increasing the income vulnerability for the farmers households. According to Kenya’s Green Belt Movement, “Many of the farmers were forced to switch from producing food, most commonly maize to growing tobacco, in the case of [BAT]. Now that they can no longer grow maize for personal use, and the return on the hard labor given to BAT are extremely low, [farmers] are now unable to either produce food crops to eat or buy food due to their low returns.” Bonded labor, also called debt servitude, in tobacco farming exists in Brazil, Malawi, Uganda, India, and other developing countries. The United Nations Supplementary Convention on the Abolition of Slavery, the Slave Trade, and Institutions and Practices Similar to Slavery defines bonded labor as “the status or condition arising from a pledge by a debtor of his personal services or those of a person under his control as security for a debt if the value of those services as reasonably assessed is not applied towards the liquidation of the debt or the length and nature of those services are not respectively limited and defined.” Bonded labor occurs in tobacco farming when a person who wants a loan but has no security to obtain a loan agrees to provide his labor or someone under his control as security to obtain a loan. 

The studies were terminated three weeks after the herbicide treatment.Statistical analysis of the field data was carried out using R v.4.2.1 with mixed model regression analysis for the visual ratings and rice grain yield data . A generalized linear model with a gaussian function was implemented for weed and rice tiller count data . Mean separation with Tukey’s HSD at α=0.05 was implemented where appropriate. Greenhouse study data were subjected to mixed model regression analysis and mean separation with Tukey’s HSD at α=0.05, when appropriate using R v4.1.2 . Data transformations were performed as needed by visually assessing the models with quantile-quantile plots and plotting residuals.Pendimethalin applied alone at 1.1 kg ha-1 caused the lowest Echinochloa control at 14 DAT; however, increasing pendimethalin rates to 2.3 and 4.4 kg ha-1 did provide greater control levels . The grass control demonstrates that pendimethalin cannot be a standalone herbicide; however, when rates were greater than 2.3 kg ha-1 grass control was increased. The foliar active herbicides in the mixtures provided good grass control for Echinochloa control and no antagonistic effect was observed. An additive trend was observed with the pendimethalin rate of 4.4 kg ha-1 adding greater value to the overall control compared to the lower pendimethalin rates . Cyhalofop and bispyribac-sodium are excellent Echinochloa herbicides, while propanil has suppression activity on Echinochloa . Despite the differences in Echinochloa populations by year,Echinochloa counts in the pendimethalin mixture treatments were similar to the standard treatment of clomazone followed by propanil plus triclopyr in both years .

Bearded sprangletop populations in the field site are low and typically controlled with the continuous 10-cm to 15-cm flood level . The non-treated had four emerged sprangletop per plot and no treatment decreased the number of emerged sprangletop . Cyhalofop is the only post-emergence herbicide used in the study with activity on sprangletop and it is not surprising that cyhalofop treatments had excellent sprangletop control. It is difficult to conclude that there was any benefit from pendimethalin application for sprangletop control in this study. Sedge and Broadleaf control. Pendimethalin does not have activity on sedges observed in this study. The herbicide mixtures and follow-up treatment provided greater than 91% control of small flower umbrella sedge and rice field bulrush by 56 DAT . The sedge density in the pendimethalin alone treatments were 143 m-2 and similar to the non-treated which demonstrated a density of 99 m-2 . Ducksalad and water hyssop were the most dominant broad leaf species at this site. Ammannia spp. was present in the field but at low population presence with observed 95% control or greater over all treatments, most likely the Ammannia spp. were outcompeted by the crop and other weeds . Pendimethalin does not have activity on the broad leaves present in this study. Ducksalad control levels were greater than 38% control after application of pendimethalin plus bispyribac-sodium and pendimethalin plus propanil treatments early in the growing season .

After the follow-up treatment at the mid-tiller rice timing, broad leaf control increased to 89% in 2022 but not in 2023 . In 2023, the bispyribacsodium mixtures resulted in the greatest broad leaf weed control .Rice injury was minimal, only up to 8% visual injury was observed at 20 DAT . Rice root growth inhibition injury on the nodal root growing region was observed early in the growing season caused by pendimethalin; however, rice recovered from this injury and appeared normal by 40 DAT . The reduced tillers were most likely caused by increase of weed pressure during the early rice growth stage which was managed with the mid-tiller rice application later in the growing season and not caused by pendimethalin injury . Otherwise, tiller counts were similar across treatments and comparable to the standard treatment . There was no difference in plant height across treatments . Grain yields were similar across the treatments where pendimethalin was applied in herbicide mixtures resulting in 6,186 to 8,263 kg ha-1 . The pendimethalin alone treatments pendimethalin plus cyhalofop resulted in similar yields to the non-treated .Results from the greenhouse study demonstrated differences across experimental runs from the response levels measured . The second experimental run generally resulted in 1.4 times greater shoot length and is probably because at the time of the study solar radiation increases in the Northern Hemisphere and the seedlings may have received greater natural light than the previous run . Shoot length was generally similar across treatments and similarly increased throughout the sampling dates. Only the 3.4 kg ha-1 pendimethalin rate did cause 8% to 12% reduction in shoots when compared to the non-treated on both experimental runs by 14 and 21 DAT .Shoot biomass was not different among treatments at all sampling dates and both runs . These results demonstrate that pendimethalin applied to four-leaf stage rice can result in shoot reduction and the level of injury is rate dependent. Root length was reduced 15% only at the 7 DAT at the 10-cm flood depth compared to the 5-cm flood depth in the first run but not the second run . However, there were no differences in root length observed by 21 DAT. In general, root biomass was not affected by the two flood depths; however, only at 7 DAT at the first run root biomass was greater at the 5-cm than the 10-cm flood depth averaged over rates but no difference by 14 DAT . The 3.4 kg ha-1 pendimethalin application reduced root biomass, averaged over flood depths, by 54% in the first run at 14 DAT and no reduction by 21 DAT and in the second run .Pendimethalin applied alone did not provide adequate weed control. Therefore, herbicide mixtures would need to be incorporated into a successful weed management program. The results from the field study show no antagonistic effect from these particular herbicide mixtures with pendimethalin and the importance of herbicide combinations to manage the different weed species in the field is emphasized. Osterholt et al. also demonstrated pendimethalin to have no antagonistic effect on quizalofop control of emerged barnyardgrass when applied as a tank mix on dry-seeded rice. In this study, it was difficult to observe a grass control benefit from pendimethalin in the herbicide mixtures. However, drying rack weed the study demonstrated reduced rice injury from pendimethalin as a post-emergence application and similar grain yields to the standard treatment. Different fields have different weed populations .

Further work is needed to incorporate pendimethalin in water-seeded rice and understand uses and benefits for weed control in the water-seeded system across different sites. The pendimethalin alone treatment followed by cyhalofop plus florpyrauxifen-benzyl resulted in lower control of sedges because at the time of application the sedges may have been too large . In addition, an antagonistic effect resulting in mixing cyhalofop with florpyrauxifen-benzyl cannot be ignored . The broadleaves present in this study are typically easily controlled with bispyribac-sodium, propanil and florpyrauxifen-benzyl; however, differences in the population density each year can be a factor to the observed reduced control the second year in the field study . The yield decrease caused by pendimethalin plus cyhalofop may be due to lack of sedge and broadleaf weed control. The herbicides bispyribac-sodium and propanil have broad spectrum activity on Echinochloa, sedges and broadleaves . The yield decrease observed in the pendimethalin alone treatments most likely was caused because of the late application not controlling emerged grasses and other weeds . The grasses not controlled increased the interference time with the rice which would explain the reduction in tillers and grain yield . Pendimethalin is not highly water soluble, non-ionizable and not hydrolyzed in water; however, it has a high affinity for organic matter . Therefore, the flood depth may have minimal effect on the molecule’s activity. These characteristics can be the reason why no effect was observed from the different flood depths, since the pendimethalin molecule will tend to readily attract to the soil surface with no lateral or vertical movement . The greenhouse study results demonstrate a reduction in shoot length but not shootor root biomass or root length after a pendimethalin application in water-seeded rice at a four leaf stage application and no consistent effect from the two flood depths tested.The application of pendimethalin alone did not result in weed control greater than 63%; however, control was increased when pendimethalin was applied in herbicide mixtures. Pendimethalin should be used in conjunction with other herbicides. Pendimethalin did not cause substantial injury when applied at 4- to 5-leaf stage rice even at the 4.4 kg ha-1 rate application. The rice recovered from minor early-season injury and grain yields across treatments with pendimethalin in mixtures were comparable to the standard treatment. In general, the results suggest that flood depths are not likely to have an effect on the level of rice injury from a pendimethalin application. Therefore, pendimethalin can be incorporated with reduced injury to water-seeded rice as a post-emergence application.These studies were funded by the California Rice Research Board. The authors would like to acknowledge the California Rice Experiment Station for providing the field site, greenhouse and assisting with the field management. The authors acknowledge the various lab members and technicians that helped with carrying out the studies. The authors also acknowledge the D. Marlin Brandon Rice Research Fellowship by the California Rice Research Trust, the Horticulture and Agronomy Graduate Group scholarships including the Bert and Nell Krantz Fellowship and the Jack Pickett Agricultural Scholarship, the William G. and Kathleen Golden International Agricultural Fellowship, and the Department of Plant Sciences, UC Davis for the award of a GSR scholarship funded by endowments, particularly the James Monroe McDonald Endowment, administered by UCANR which supported the student.Rice is a major crop, valued for its nutritious components as a food crop and produced worldwide . In the US, rice production is centered in Arkansas, California, Louisiana, Texas and Mississippi producing nearly two million metric ton of grain for the export market in 2022 . Weed management is a major challenge to achieve economically viable production levels. Cultural practices to achieve an integrated weed management program in California rice include use of certified seed, proper land preparation, and water management . However, to reach the economically viable rice yields, herbicides are necessary to control weeds . The limited number of available herbicides and continuous rice cultivation year after year in California have selected for herbicide-resistant weeds and have caused a reduction in weed control from the available herbicides . The lack of crop rotations makes water management and herbicide use the most important tools to manage weeds . Therefore, new herbicide modes of action are needed to help manage herbicide resistant weed populations. California rice is uniquely different from the other US rice producing states because nearly 90% of the production is medium-grain rice and produced in a water-seeded system .

Excellent reviews evaluating dinitroaniline mode of action and behavior in plants have been performed by Parka and Soper , Appleby and Valverde and Chen et al. . The mode of action of pendimethalin and other dinitroanilines is inhibiting the mitotic pathway of cell division by preventing the assembly of the microtubules. Microtubules are protein-like organelles that are made up of α- and β-tubulin molecules which are heterodimers and form the mitotic spindle which orient cells and direct the cell division . During cell division, the microtubules create the mitotic spindle by polymerizing the tubulin dimers. In the presence of the herbicides the tubulin does not polymerize. The herbicide molecule will bind to the α-tubulin, which prevents the β-tubulin from docking and polymerization cannot be continued. The polymerization inhibition leads to the halt in cell division, which cause the accumulation of incomplete cells in one area and create the anatomical feature of swollen or clubbed root tips and stunted growing points. Dinitroanilines exclusively bind to plant cells and do not bind to animal microtubules . There is evidence which suggests dinitroanilines also inhibit the calcium uptake in the mitochondria. Cytoplasmic calcium is a regulator of cell cycle and redistribute among theorganelles and cytoplasm . Studies by Hertel and Marme demonstrated dinitroaniline compounds caused Ca2+ to accumulate in the cytoplasm at 10-4 M nmol mg-1 protein concentrations, which could cause interference with microtubule assembly and cell division.

However, Morejohn et al. reported oryzalin to depolymerize microtubules at very low concentrations . Therefore, Appleby and Valverde concluded it was unlikely that the effect of calcium regulation would depolymerize microtubules. The calcium deregulation may be a side effect of the dinitroaniline compounds that can affect plant growth when applied post-emergence, but is not the herbicidal mode of action. Additional evidence also suggest dinitroaniline herbicides can affect guard cell functions when applied on the plant foliage in lab studies. Marcus et al. demonstrated microtubule inhibitors prevented stomata guard cells to open, then, re-open after application of drugs that blocked the microtubule-inhibitors. Microtubules remain present in guard cells after cell differentiation and function as a guiding mechanism and signal mechanisms for the opening/closing of guard cells . Marcus et al. tested fusicossin, a drug that induces guard cell opening by activation of the proton pumps, after use of microtubule-inhibitors which caused the guard cells to reopen after being signaled to close by the microtubule inhibitors. These results may indicate the role of microtubules in signal transduction of protons like the Ca2+ activity in guard cells which acts to open and close stomata . The results support the observed regulation of Ca2+ by Hertel and Marme . Other effects from dinitroaniline herbicide applications include oxidative cell damage by reactive oxygen species that are created in response to the stress in treated plants and reduced absorption and translocation of nutrients in treated plants .

However, these effects also are observed in relatively tolerant crops and do not contribute to the primary herbicidal mode of action but can be important in suppressing plant growth. Weed Resistance. While resistance to dinitroaniline herbicides is limited, there have been cases reported on 12 weed species including Alopecurus aequialis, A. myosuroides, Amaranthus palmeri, Avena fatua, Beckmannia syzgachne, Echinochloa crus-galli var. crus-galli, Eleusine indica, Fumaria densiflora, Lolium rigidum, Poa annua, Seteria viridis and Sorghum halepense . The relatively low number of resistance cases may be attributed to lack of documenting or due to the typical practice of applying dinitroanilines in combination with other herbicides. The relatively low resistance could be due to possible fitness costs associated with the resistance mechanisms . In most crops, dinitroanilines are used as part of an herbicide program and suspected herbicide-resistant plants are controlled with the preemergence herbicide mixtures applied early in the season and any surviving plant after the preemergence application are likely to be controlled with a post-emergence herbicide with a different mode of action later in the growing season . Resistance mutations in the α-tubulin genes have been documented in dinitroaniline resistant populations inducing target-site resistance . The resistance-endowing mutation, Thr-239-lle, was initially reported in E. indica and later also in L. rigidum . Other resistance-endowing mutations are presented and explained in the review by Chen et al. . There is evidence of fitness loss from the dinitroaniline-resistance mutation Arg- 243-Met resulting in a severe reduction in plant biomass accumulation . Non-target site resistance mechanisms to dinitroanilines are not common; however, there is not to many research many research on the subject matter probably because of the difficulty in quantifying metabolites in plants . Early research demonstrated degradation of pendimethalin in tolerant plants, but no single metabolite was more abundant and in some species the parent molecule was the majority recovered residue . However, there is some indirect evidence of metabolic pendimethalin degradation in multiple resistant populations . The cytochrome P450 genes which Han et al. identifies as responsible for metabolic resistance have been documented to confer resistant to many herbicides and would not be surprising if they contributed to resistance mechanisms against dinitroanilines . Crop and Weed Tolerance. Lipid content in plant has been associated with tolerance to dinitroaniline herbicides. Hilton and Christiansen and Ndon and Harvey demonstrated that lipid content in the seed or roots of the tolerant species can bind the herbicide and prevent it from reaching the site of action. The results agree with the physico-chemical properties of the dinitroanilines, 4×4 plastic tray which are lipid-soluble and attracted to lipid-rich plant tissues.

In general, broadleaves have greater lipid content in seeds, roots and shoots than grasses, but a positive correlation of lipid content with relative dinitroaniline herbicide tolerance has been observed in grasses such as corn, foxtail, sorghum, and oats . The lipid binding is a major mechanism of tolerance to dinitroanilines in carrots, Daucus carota . Safening to dinitroanilines has been demonstrated with applications of lipid type substances to seeds or soil in various plant species . Herbicide placement has been an important action for improving crop tolerance. The dinitroaniline characteristics suggests they will bind to organic matter and not be readily leached; therefore, injury occurs based on the proximity of sensitive plant parts to the herbicide . The majority of dinitroaniline herbicides will remain in the upper 7.5 cm of the soil after an application . In green foxtail, Setaria viridis, an application of trifluralin in the soil shoot zone caused similar injury to an application in the seed zone, and greater injury than a root zone application, indicating the early shoot herbicide absorption is important for injury on grasses . Planting the crop seed deeper in the soil can be a management action to prevent contact with the herbicide in the crop’s sites of absorption.The use of dinitroanilines in rice production systems was not widely adopted before the 1980’s because of the potential for significant rice injury . However, various research efforts further expanded their potential use in rice systems . Koger et al. performed studies to understand effects of rice cultivar, planting depth and rainfall on crop safety after a pendimethalin application in dry-seeded rice. A cultivar effect was observed in three long-grain cultivars and was attributed to the varying mesocotyl lengths. An elongated mesocotyl may mean increased herbicide absorption on the soil surface, while a shorter mesocotyl length would reduce herbicide absorption at the seedling growing point on the soil surface. Therefore, it was observed that deeper planting led to greater crop safety to the pendimethalin. Khaliq and Matloob suggested a similar mechanism to pendimethalin tolerance in a dry-seeded system. Awan et al. and Ahmed and Chauhan determined rice injury from pendimethalin is affected by soil moisture and application rate in dry-seeded rice. By delaying the soil saturation time up to 7 days after seeding and pendimethalin application, rice injury can be reduced; however, in comparison with other preemergence herbicides, pendimethalin causedthe greatest injury levels . The decrease in grain yields and increased injury levels reduced adoption of pendimethalin by growers in dry-seeded rice . In drill-seeded rice, pendimethalin is commonly used. The selectivity mechanism is deeper rice seed planting. Koger et al. reported that planting depth is influential in enabling crop safety to pendimethalin. When rice seeds are placed 7 to 10 cm in soil, it prevents the growing points from coming in contact with the herbicide on the soil surface, while the herbicide can control the weeds seeds emerging on the soil surface . Pendimethalin has successfully been incorporated in drill-seeded rice systems of the US Mid-South. Pendimethalin has been a useful herbicide to manage propanil-resistant barnyardgrass in the Mid-South . Pendimethalin can be mixed well with other herbicides and is incorporated as a post-emergence application to overlay soil residual herbicide activity .Barrett and Lavy evaluated pendimethalin dissipation in common aerobic and nonaerobic cropping systems. The systems evaluated included soybeans , upland rice and lowland rice . Barrett and Lavy demonstrated soil half-lives of 3 to 7 days in lowland rice and upland rice, while half-lives were 7 days in the first year and nearly 20 days the second year in soybeans. The results indicated that soil-water content was a significant factor in pendimethalin dissipation and these results were supported by Savage . Barrett and Lavy described the dissipation spectrum as rapid dissipation in lowland rice > upland rice > soybeans, which was most likely caused by the alternate wetting intervals in the rice croppingsystems that accelerated the dissipation. The dry/wet soil cycles would have increased volatilization in the dry soil and reduce the concentration of pendimethalin . Weber suggests volatilization decreases in anerobic or flooded conditions where pendimethalin vapor moves less readily in the wet soil compared to movement in dry soil with more open pore space. Makkar et al. demonstrated pendimethalin soil dissipation in dry-seeded and transplanted rice fields to follow a biphasic first-order dissipation. The biphasic first-order dissipation results in a rapid initial dissipation after application followed by steady a dissipation rate. The behavior is commonly observed with other dinitroaniline herbicides . The dry-seeded rice was in non-flooded conditions and flush irrigated, while the transplanted rice was continuously under flooded conditions . Similar to Barrett and Lavy , Makkar et al. demonstrated total pendimethalin dissipated 1 to 2 days faster at the initial phase and about 10 days faster at the final phase in the transplanted rice field when compared to the dry-seeded rice field . The pendimethalin fate in a flooded rice field is most likely binding to organic compounds in the soil . Microbial and photodegradation are other important pathways that can contribute to degradation ; however, the binding action to organic matter appears to be most significant in many environments . In water-seeded rice, behavior of herbicides in the water is important to study. There are many herbicides that need to be activated with the water and perform best in the flooded conditions, while there are herbicides that are absorbed by the foliage and the flood will decrease efficacy .

Since cabbage looper and Diamondback moth make the majority of the total insect pests , pot growing systems broccoli leaf damage for 2007 must have been caused primarily by those two insect pests.Total insect parasitization for 2007 varied among cropping treatments and there was a significant interaction between cropping treatment and sampling week . Total insect parasitization for most of the sampling weeks was significantly higher for the cowpea and marigold treatments, compared to the fallow; however as of the last sample date, there was no significant difference among treatments . Insect parasitism is species specific. Parasitization rates reached very high levels for all three species on at least some sampling dates . Cover crop treatments did not have a significant effect on insect pest parasitism for any of the three species pooled over the season, but the effect for cabbage looper was close to significant . There also was a significant interaction between treatment and sample date for cabbage loopers and cabbage looper had significantly higher levels of parasitism in the marigold plots than in the other plots on the first sample date. Parasitism of cabbage looper was significantly higher in the cowpea plots than in the other plots on the fourth sample date .Total insect population densities for this year varied not only among sampling weeks , but also among cropping treatments with no significant interaction between treatment and sample date .

Total insect population was significantly higher in the cowpea treatment than on either the fallow or marigold treatments; there was no significant difference between marigold and fallow. Total insect population at early crop growth season was relatively higher than at the same time total insect population levels in 2007 , but exhibited a single population peak rather than two. The single seasonal total insect population peak was attained in the middle of the broccoli growing season and then declined . The population peak in 2008 was higher than in either 2007 or 2009. At their peak population levels , total insect pest population was consistently higher for the cowpea treatment compared to the fallow treatment with no significant differences between cowpea and marigold and marigold and the fallow treatment .Within individual insect species, both cabbage loopers and cabbage worms responded significantly for the cropping treatments with populations reaching significantly higher levels on the cowpea treatment than on the other two treatments . Cabbage loopers and diamondback moths both exhibited a single mid-season population peak with cabbage loopers reaching a higher peak than diamondback moths . As in the previous year, the density of cabbage worm was much lower than the density of the other two species .Broccoli leaf damage for 2008 varied among cropping treatments and sampling weeks . Their interaction was not significant.

Damage was significantly higher in the cowpea plots than in the fallow plots and almost significantly higher in the marigold plots than in the fallow plots . Leaf damage rose steadily over the first four sample dates in all plots, continued to rise in the fifth and sixth sample dates in the cowpea plots, but flattened over weeks 5 and 6 in the marigold and fallow plots .Parasitization rates reached very high levels on at least some sampling dates, especially for cabbage looper . Total insect pest parasitization in 2008 differed significantly among cropping treatments and sampling weeks , with no treatment and sampling week interactions . Total insectparasitization levels in 2008 were significantly higher for both cowpea and marigold , respectively compared to the fallow treatment . Among the individual insect species, parasitism did not vary significantly among the treatments for any of the three lepidopteran pests , although there was a significant interaction between treatment and week for diamondback moth. Breaking down parasitism by week for diamondback moth revealed that parasitization was significantly higher in the cowpea plots than in the marigold and fallow plots on one early season sampling date and was significantly higher in the marigold plot than in the fallow plots on the last two sampling dates .Total insect population for 2009 was not significantly variable among cropping treatments , but did vary significantly among sampling weeks . The treatment-sample date interaction was not significant. There were two distinct total insect population peaks . Considering the individual insect population densities, none of the three species differed among the treatments . Both the cabbage loopers and diamondback moths exhibited distinct mid and late-season population peaks whereas, cabbage worm had only an early season peak and was scarce thereafter . However, the diamondback moth had only one population peak in the fallow treatment .Leaf damage in 2009 was significant for the cropping treatments, sampling weeks, and the interaction between cropping treatment and sampling weeks . Early season through the first pest population peak, damage was significantly higher in the cowpea treatment than either marigold or the fallow treatments . On the third sample date, damage also was significantly higher in the marigold plots than in the fallow plots . In mid season there was no significant difference in damage among treatments . Near the beginning of the late season insect pest population peak in 2009, crop damage was significantly greater in the fallow plots than in both the cowpea and marigold plots . There are two peaks of total insect pest density but only a single peak leaf damage , indicating that crop damages do not correspond to insect population densities. Crop damage patterns do not also correspond to the bimodal population peaks observed for cabbage loopers and diamondback moths in 2009 . However, considering the larger individual feeding larval sizes of cabbage loopers, it can be assumed that the cabbage loopers were responsible for most of the broccoli leaf damage. The very low number of cabbage worms indicates that little damage can be attributed to this species.The overall model for total insect parasitization for 2009 was significant among the cropping treatments , with both the cowpea and marigold plots experiencing significantly higher levels of parasitism than the fallow plots. There was also a significant effect of sampling date and an almost significant treatment sample date interaction .

The significant difference among treatments was a group effect of all three species pooled as none of them individually showed a significant effect of treatments on parasitism although the effect of treatment on cabbage looper parasitism was almost significant .In general, planting racks three lepidopteran insect pests; the cabbage looper , the diamondback moth and cabbage worm were observed as the major broccoli insect pests throughout the study years. Overall pooled for three years, total insect population densities and cabbage worms were higher on the cowpea cover crop compared to the fallow system. However, cropping treatments pooled over the three year study had no significant effect on the overall population density of cabbage loopers and diamondback moths. The overall analysis for data pooled over all three years showed significance levels for the cropping treatment and year. Higher total insect population was observed in 2008 than any other year, probably because broccoli growth for this year was more robust making it more attractive to insect herbivores. In all years, total or individual insect population started with low levels during early crop growth season, increased over a period of time and attained either single or multiple population peaks. The knowledge of pest population peaks may help plan insect pest management timing and control strategies. Cover cropping treatments had a significant effect on total insect population densities as well as on cabbage loopers and cabbage worm population densities only in 2008. During this year, the higher insect population levels were attained on the cover crop treatments, particularly the cowpea compared to the fallow treatment. In contrast, insect population densities for 2007 and 2009 were not affected significantly by cover cropping treatments. Therefore, considering the three year data, it can be said that the off-season cover cropping treatments had very little or no effect in suppressing either the total or individual insect pests. If at all, the cover crops rather enhanced pest population densities on the subsequent vegetable crop as was observed in 2008. The greater insect population density on the cover crop treatments for 2008 crops may have been due to better growth, higher nutrition and a broader canopy that was observed in the broccoli crop in 2008 . Based on the three year population dynamics and peaks, the presence of multiple population peaks for the cabbage loopers and diamondback moths may indicate that insect pests are the most important insect pests of broccoli. Sarfraz et al. considered that P. xylostella is a major constraint to brassica crop production, while Furlong et al. recognizes A.rapae as the most devastating pest. These variable categorizations of pest severity could be due to geographic differences and possible year to year variations. In this study, cabbage worms attained far lower population densities that the other lepidopteran pests during all three years.In this study, off-season cover crops had little or no effect on pest population densities. In studies where cover crops were interplanted with the main crop, reduction in pest populations has been reported from several studies. Broad et al. detected a reduced colonization of diamondback moth within the diversified cropping systems, indicating that more insect pests under a mono-cropping system. On the other hand, in a mixed broccoli intercropping system, Hooks and Johnson found higher populations densities of cabbage worm. The more abundant herbivorous insect pest density in monoculture compared to polyculture may be attributed to a ―resource concentration‖ hypothesis where some specialist herbivores may respond more strongly to homogeneous systems than to mixed cropping. These contrasting observations suggest that the success of cover cropping treatments as insect pest suppressant depends not only on cropping diversification, but also on the scale and the timing of the diversification . The early season increase in broccoli leaf damages in all years could be attributed to the influx of colonizing insects. Broccoli leaf damage varied significantly among cropping treatments in 2008 and 2009 but not in 2007. In 2008, broccoli leaf damage became conspicuously higher in the cowpea cover crop plots compared to the fallow plots only late in the season. In contrast, in 2009 the greater damage on cowpea versus fallow plots occurred only early in the season. Broccoli plants abscise damaged or older leaves very frequently and hence the reason why leaf damages may not progressively increase in each year.Numbers of insect damaged leaves in 2007 were lower than the peak leaf damage observed in either 2008 or 2009, but the increase in leaf damage does not necessarily synchronize with the dynamics of insect population densities in most of the crop growing years. Within the insect populations, the fact that cabbage looper and diamondback moth were the majority of the total insect pests, suggests that these insect species must have contributed the most to broccoli leaf damage. Yet, since cabbage looper population density accounted most for the total insect population densities and has larger larval sizes, crop damage can be attributed mostly to cabbage loopers and to a lesser extent to diamondback moth and little to the cabbage worm. Nevertheless, crop pest damage is a cumulative effect of all insect pests; hence consideration of total insect pest population should provide a better depiction of insect and insect management decisions.

We explained and gave examples of possible potential applications and further data analysis based on the johnsongrass map we created. We compared the cost of the car survey, human-based GSV survey, and AI-based GSV survey, and the result demonstrated that the AI-based GSV survey could spend much less time and money on larger-scale roadside species mapping. However, our method cannot retrieve images on a specific date for a single location as the current Google API always returns the latest images to us from their database. Our methods can be improved as the GSV database increase the size and provide more options for images from a single location but at different time. Overall, our work presented that an AI-based GSV survey can be cost-effective on roadside invasive species surveys. Future work will focus on expanding the scale of johnsongrass mapping, and our model will be applied to other invasive species to create more large scale distribution maps.Conventional weed management practices that solely depend on intensive use of herbicides are known to cause ecological and health hazards , and have triggered societal demand for alternative weed management strategies . Effective and sustainable weed control is also a top priority for organic agriculture . The National Organic Regulations and Guidelines prescribe the use of preventive measures as a first line of defense against weeds and other crop pests with no chemical weed control. Because of the lack of effective non-chemical weed management strategies, certified organic croplands in the US faces insignificant increases .

One of the fast growing alternative weed management strategies that may fulfill an ecologically desirable pest management alternative is the use of cover crops . Cover cropping systems involve the use of live plants or their residues as surface mulches . Cover crops not only suppress weeds, but may also improve growth and productivity of the subsequent crops . Many authors showed the usefulness of cover crops as a weed management strategy, but most were from cover crop inter-planting with the main crop . Growers are hesitant to use cover crop inter-planting, asbecause of competition for resources and yield reduction of the main crop . This makes the off-season cover cropping rotation a preferred alternative. However, relatively little evidence exists for the weed management potential of offseason cover crops. Limited resources show that off- season cover crops may provide added economic benefits including soil preconditioning, and supply of additional nutrient to the subsequent crop . This research assessed the effectiveness of summer cover cropping systems for weed management in a winter broccoli crop. More specifically, it evaluated the responses of major weed population densities and their respective biomass to two cropping strategies; through a) planting two different cover crops as a summer rotation after which the vegetable crop is planted for growth during the subsequent season and b) planting the primary vegetable crop on a summer fallow treatment. In order to assess the additional effects of summer cover cropping, we examined soil weed seed bank and the time it may take for hand weeding in each cropping treatments. It was proposed that cover crops reduce soil weed seed pressure and the need for supplemental weed control.A three-year field study was conducted from 2007-2009 at the University of California South Coast Research and Extension Center in Irvine, CA on a loamy-sandy soil.

Three summer cropping treatments were employed: 1) French marigold , 2) cowpea , seeded at 56 kg/ha, and 3) a summer dry fallow as the untreated control. Cowpea was chosen because it is a drought hardy legume, resistant to weeds and enhances some beneficial organisms . Marigold was chosen because it is known to control a broad range of nematodes . Each treatment plot was 12 m long x 10.7 m wide . The cover crops were direct-seeded in the last week of June in the center of 14 planting rows of each treatment plot, watered through drip-tubing and grown for three months. The fallow control plots did not receive water during the summer. Each cover crop treatment plot was planted with the same cover crop in each of the three years of study. Plots were separated from each other with a 3 m wide buffer bare ground. The three treatments were replicated four times in a completely randomized design. At the end of the summer cropping period , the cover crops were mowed at the soil line, chopped, and the residues left on the ground. Concurrently, alternate rows of each of the cover crop treatments were incorporated into the soil at about 0.4 m intervals using a hand-pushed rotary tiller in preparation for broccoli transplanting. The fallow plots were not tilled. Plots for cover crop and broccoli planting are shown in Figure 1a. At the beginning of the subsequent cropping season , broccoli seedlings were transplanted in double rows into the tilled strips of the summer cover crop and fallow plots at an inter and intra-row spacing of 13 and 35cm, respectively . Broccoli transplants were drip irrigated and fertilized with emulsified fish meal at 5 gallons/acre rate. Broccoli was chosen because it is a high-value vegetable crop that is sensitive to weeds, insect pests, nematodes , and requires high soil nutrients . All plot treatments were maintained in the same location for all three years of study in order to assess a cumulative effect of cover crops over time.Weed population density was obtained by sampling at 4 , 8 , and 12 weeks after broccoli transplanting. Weed population count was accomplished using a 50 cm x 50 cm quadrat randomly thrown twice within each treatment plot, grow tray then counting each weed species that had emerged within the quadrat. The population density of each weed species within a plot was recorded as the average of the two quadrat counts. Following the early and mid sampling periods, all plots were hand weeded, recording the duration of time required for weeding. Weed dry biomass was determined by clipping the aerial portion of each weed species observed within each quadrat, drying the samples for 7 days at 700C, and then weighing. The total weed dry biomass of each weed species was recorded and averaged for the two quadrat samples taken per plot. All weed species population density and dry biomass data were analyzed using ANOVA and the means separated using the student T-test.Soil samples were collected three times during each of the three trial years; at the time of cover crop planting , at the time of cover crop incorporation and at broccoli harvest . For each treatment plot, a W-shaped pattern was followed to collect twenty soil cores of 10 cm deep each following soil sampling procedures of Forcella et al. . Weed seed populations from each sampling were assessed using a simple greenhouse weed seed germination test. A set of 500 g soil from each of the sampling periods were spread in flats, placed in the greenhouse and kept moist and well drained. The soil was stirred after the 1st two weeks to expose buried seeds to light and trigger germination. Emerged seedlings were counted and removed every two weeks for one month. After one month, the soil was placed in a cold room for 30 days to simulate conditions needed by some weeds for breaking their dormancy and again placed in the greenhouse for one month and germination counted again.

Weed seedlings were identified to species and the number of individuals that had emerged from each sample was recorded and pulled from the flats at regular intervals. Flats were checked regularly at 3-4 day interval for newly emerged seedlings to assure that no plants emerged and died between counting.The most dominant weed species during all years was Portulaca oleracea , accounting for 70-85% of all weed populations. Other weed species wereChenopodium album , Solanum nigrum , Amaranthus species , Malva nicaeensis , Sonchus oleraceus , Convolvulus arvensis , Capsella bursa-pastoris and Erodium cicutarium . Urtica urticaurens and Oxalis corniculata were observed in some plots, but rarely. Data on weed population densities were presented in Table 1.1 , Table 1.2 , and Table 1.3 . Population densities of common purslane at the early sampling of 2007 were significantly lower for the cover crop treatments compared to the summer fallow . At this sample date, which was just before the initial hand weeding the population density of common purslane within the fallow summer plot peaked at 370 plants per m2 Therefore, the cover crops reduced purslane populations to one-fifth and less than one tenth in broccoli that followed either a summer cowpea or marigold cover crops, respectively. All weed population densities following initial hand weeding were generally low for all treatments and did not vary among the cropping treatments. However, the total population density of all weeds combined, mostly accounting for variations in purslane population densities was lower by 5 and 4 times if broccoli followed summer marigold and cowpea, respectively, compared to these on a fallow plot . Cover crop weed population suppression was more prominent against broad leaves than grass weeds. Grass weeds were generally of low densities and were unaffected by the summer cropping treatments of the first year . Weed population densities at mid and harvest time sampling were lower than the early sampling period . The individual weed population densities at the mid and harvest time sampling were not significantly different among cropping treatments , except for higher total broad leaf and the combined all weed species in the fallow compared to both cover crop treatments . Weed population densities for the early sampling of the second year resembled that of the first year , with Portulaca oleracea remaining as the most dominant weed. The effect of cover crop weed suppression was also similar. Accordingly, the population density of Portulaca oleracea at early sampling of the second year was reduced by 3 or 4 times if broccoli was planted after summer marigold or cowpea respectively, compared to the summer fallow . The supplemental hand weeding further reduced weed population densities for 2008 as can be seen from the lower weed population densities during the mid and harvest time sampling . At mid-season and harvest time samplings of 2008, population densities of common purslane were still was significantly lower in the cover crop treatments compared to the fallow . Similar to the 2007 observation, the broadleaved weeds were still more suppressed with cover cropping and hand weeding interactions that the grass weeds. Weed population densities during the third year were generally lower than the previous two years. Common purslane was the most abundant weed for early sampling of 2009, but was reduced by 6 and 12 times in marigold or cowpea treatments, respectively compared to the fallow treatment . Cover crop suppression of Solanum nigrum , Amaranthus species and Erodium cicutarium became significant only for this year. The cover cropping treatment continued to suppress common purslane and Amaranthus species at mid sampling in 2009. The population densities of these weeds at the mid sampling were lower for the summer cover crop than the fallow treatment .

Blue River says a viable version of its technology for cotton is still several years from commercial release . In vegetable crops, as with commodity crops, existing herbicides are becoming less effective, said Steve Fennimore, a UCCE weed specialist based in Salinas. But the prospects for new herbicides suitable for vegetable crops are even dimmer than those for commodity crops because vegetable crops represent a relatively small market for chemical makers. “The chemical industry invests very little — essentially nothing — on these crops,” Fennimore said. Due to the complexity of chemical development and the high cost of the regulatory approval process, large chemical companies are effectively the only entities capable of commercializing a new herbicide, for any crop. But for automated weeding, Fennimore noted, there are essentially no regulatory hurdles, and it doesn’t take the resources of a giant company to develop working prototypes. Small firms can innovate meaningfully. As a result, Fennimore said, the best prospects for advances in vegetable weed control are likely to be through improved machines, developed by small firms and growers, with support from UC and the research community.Currently, automated weeding systems work well in relatively simple settings — low weed density, little or no overlap of weeds and crop plants. In more complex settings, current image-recognition technology struggles to reliably identify which plants should be removed. David Slaughter, UC Davis professor of biological and agricultural engineering, is working with nine collaborators — from UC Davis, UCCE, Washington State University and the University of Arizona — on a $2.7 million USDA-funded project to improve mechanized weed control by developing better systems for what’s called crop signaling — distinguishing crop plants from weeds.

One approach uses a biodegradable straw with a fluorescent coating inserted into the soil with the crop plant. The coating is readily detected by a camera, which can then tell the weeding equipment which spots to avoid. Another crop-signaling method uses high-precision GPS to record planting locations. “We can make a map of every seedling,” said Slaughter. When it’s time for weeding, all plants that aren’t on the map are removed. Slaughter noted that another general path of evolution for automation is the adaptation of growing practices — plant spacing, crop varieties, the timing of weeding and so on — to suit the available technologies.Harvest is generally the most costly step in vegetable production, due chiefly to the amount of labor required. Salinas-based Taylor Farms, the world’s largest salad producer, has invested heavily in harvest automation, developing romaine lettuce and cabbage harvesting equipment used by the growers it contracts with to supply the bagged salad market . But for many vegetable crops, as well as other major Central Coast crops like strawberries, effective automated harvesters have yet to be proven. “Automating the harvest — that’s the Holy Grail for pretty much everybody,” said Brian Antle, who runs the planting automation company PlantTape and is a member of the family that co-owns Tanimura & Antle, one of the largest fresh produce growers in the Salinas Valley. An intermediate step is “co-robotics” — designing robots to work alongside human laborers, with the robots handling simple tasks while people continue to perform the more complex and delicate actions.

One example is self-guided carts that assist human strawberry pickers by carrying full trays of strawberries out of the field and returning with empty trays. “The recognition is that the agricultural environment is very complex, and we may not see full autonomy in the next decade,” said Slaughter.In the 1960s, the release of a processing tomato harvester, developed by two UC Davis researchers, transformed the production of that crop. Only larger growers could afford one, and because the machine dramatically reduced the costs of harvesting, it created a powerful economy of scale that encouraged big growers to expand. In the first few years after the harvester’s introduction, a large fraction of the state’s tomato growers left the business. Advocates for small farmers and farm workers organized to criticize UC’s role in developing the harvester and to push for more UC support for small farmers. In a 1979 lawsuit, they argued that the tomato harvester favored large farmers, violating the public benefit mission of land-grant university research as established by the Hatch Act of 1887. UC prevailed in court after a 10-year legal battle. But the conflict drove lasting changes at UC and elsewhere. Federal funding for automation research declined, and agricultural engineering departments shifted focus to other types of research, Slaughter said. Today, UC ANR programs targeting small farms include the Sustainable Agriculture Research and Extension Program and the UC ANR Small Farm Working Group. Like previous waves of mechanization, automation in vegetable crops stands to mainly benefit larger farms, at least initially. Large, highly standardized fields of a single crop tend to be better suited to mechanization than the fields of a small farm growing a variety of crops. And, as noted earlier, large growers are currently the main market for — and often the lead investors in — novel automation technologies, which tend to be designed to solve the problems they face on their own farms. Margaret Lloyd, a UCCE small farms advisor in Yolo County, said that automation technologies can benefit small farms too — but small growers need versions of the machines that are less expensive, more versatile, and designed with small scale in mind. “Could you make a machine that does four rows at a time, but also make one that is simpler and cheaper and only does one row?” she said.  Yes, probably, said UCCE’s Fennimore — once the technology is well developed. “Do tractors only benefit large growers? No, because we now know how to build tractors and there are lots of them, new and used, and thousands of grower customers are each paying a small fraction of the research and development cost to improve tractors,” he said. “Eventually this will be true for weeders and other smart technology.”Increased rotational production of many agronomic grass and cereal grain crops seems destined to be part of the agricultural future. This may occur, not only to produce more food for ever-increasing numbers of people and livestock on the planet, but also to provide feedstocks for lignocellulosic biofuels made from plant residues, such as from straw remaining after harvest . These crops may include the small grain staples widely grown for human consumption, e.g., wheat, rice, barley, etc., grow systems for weed as well as those grown primarily for vegetative biomass and livestock feed, such as sugarcane, sudangrass and sorghum. Increased sequencing into grass family crops may occur even in agricultural regions, such as in the Mediterranean climatic zones, where intensive relay planting of high-value horticultural crops is commonly practiced. Due to rising costs, increased scarcity of water and other resources, and the vital importance of maintaining long-term, sustainable agricultural production systems, improving cropping efficiency through value-added, or “multi-tasking” uses for all portions of crops is becoming increasingly necessary . At the same time, care must be taken so as to not remove excessive amounts of plant biomass from the land, so that soil quality and fertility suffer.

The development of pest management tactics based on use of non-harvested crop components can be an important facet of overall agricultural sustainability. It is widely known, but often not considered, that many poaceous plants possess properties that are inhibitory to other life forms . The bioactivity of poaceous plants may be based on allelopathy and/or toxicity of their decomposition products in soil . Allelopathy depends, to a great extent, on organisms producing secondary metabolites — chemical compounds not necessarily needed for their basic metabolism, but which often confer ecological advantages by killing, weakening or repelling nearby competitors for nutrients, space or other niche resources . For example, many of the synthesized antibiotics used in human and animal medicine were originally discovered as secondary metabolites of various microorganisms. Although potentially useful levels of pesticidal activity have been demonstrated from certain poaceous plants and from their decomposing residues, the broad range of these toxic properties also has resulted in undesirable instances of phytotoxicity to subsequent crops . The potential of biomass crops, primarily those in the cabbage family , for use in soil biofumigation and soil/water bioremediation was recently discussed . In previous experimentation with residues of brassicaceous and alliaceous crop plants as soil amendments, biocidal activity was shown to increase with increasing soil temperature. We also reported that cover cropping with a sorghum– sudangrass hybrid [Sorghum bicolor Moench x Sorghum sudanense Stapf. = “sudex”] was detrimental to subsequent tomato, lettuce and broccoli transplants because of allelopathic phytotoxicity . Indeed, various Sorghum spp., such as sudex, grain sorghum, sudangrass and johnsongrass , have been shown to inhibit emergence or development of a broad range of annual and perennial crop species . However, in addition to their sometimes negative impact on subsequently planted crops, the contributions of various poaceous species and cultivars on populations of weeds also must be considered . For example, significant reductions in weed populations have been reported in wheat following sorghum , and root exudates of S. bicolor reduced growth of velvet leaf, thorn apple , redroot pigweed , crabgrass , yellow foxtail and barnyardgrass . These findings point to possible pest management utility of crop rotations with agronomic grasses. In this study, our objectives were to conduct experiments with containerized soil, at laboratory scale, to test the pest management effects of amendment with residues of small grain crops. The experiments, conducted at two temperature regimens, evaluated survival and activity of the nematode plant pathogen Meloidogyne incognita, and the fungal pathogens Sclerotium rolfsii and Pythium ultimum, following exposure to cultivated wheat, barley, oat and triticale residues in soil. Furthermore, we conducted field experiments to test effects of sudex cover crop plants, previously shown to be deleterious to vegetable crop transplants , for weed control.As described in a preliminary report , Hanford fine sandy loam soil naturally infested with M. incognita [ca 150 second-stage juveniles per liter of soil] and P. ultimum [ca 29 propagules per gram of soil] was used. Laboratory-grown sclerotia of S. rolfsii were added to the soils in mesh bags prior to treatment. Soil for treatment was loaded into bioreactors, consisting of wide-mouthed, 2-liter-capacity glass jars, with openings covered by clear, 0.031 mm , low-density polyethylene film, tightly secured with rubber bands. This technique allowed for limited gas exchange between bioreactors and ambient air, and simulated conditions in field soil during solarization or bed mulching. Four replicate bioreactors were then incubated in a modified Wisconsin-type water bath with diurnal temperature maximum and minimum of 38°C and 27°C, respectively, while four others were simultaneously maintained in a similar water bath set at a constant 23°C . The elevated temperature water bath was set to deliver 8 h heating per day, which gave samples in bioreactors ca 6 h at maximum temperature during each 24-h period.

However, when cover crops were present, weed emergence was generally slower after the late planting date, especially in plots seeded with the brassica mix. Weed emergence rates after the late planting could have been affected by existing weed cover at time of late planting, due to continuous weed germination and a slow-acting burndown herbicide prior to the late planting date. Variations in weed emergence could additionally contribute to reductions in weed biomass from late planted treatments. Overall, the multi-species cover crop had faster emergence than weedy plants, and the brassica cover crop had similar emergence rates with weedy vegetation. However, quicker emergence did not always lead to enhanced weed suppression, which is consistent with previous studies that suggest that biomass, rather than functional diversity, is the most important factor in weed suppression . While cover crop mixes did not reliably slow weed emergence in this study, their germination uniformity and predictable emergence could make them a useful management tool compared to less predictable weedy vegetation. The sprayed and forage treatments had similarly increased levels of summer weed coverage compared to the three cover crop treatments that left residues in place, which were similar to one another. These results indicate that cover crop residues suppress summer weed emergence compared to treatments without any cover crop or where cover crop residues have been removed through baling.

Cover crop literature in annual cropping systems supports the value of cover crop residue for reducing summer weed emergence . In perennial systems, the spatial separation of the cover crop from the primary crop provides additional options for cover crop termination, including flexibility related to timing, repeated termination actions, and termination equipment. Future research could focus on these under-explored aspects of cover crop management in perennial cropping systems, such as by focusing on high-residue termination methods such as roller crimpers or delayed cover crop termination in the early summer. In this study, we observed that cover crops are not consistently effective as a weed control tool compared to weed management programs with repeated herbicide applications, but they continue to demonstrate value as component of an orchard vegetation management program. Such vegetation management programs allow some plant growth on the orchard floor but result in predictable plant cover and favorable orchard floor conditions for nut harvest. Orchard cover crops flourished under a variety of management programs but were most abundant with timely planting and adequate moisture during establishment. We worked in orchards that had not previously been managed with cover cropping, and any effects of cover crops on weeds could compound over the lifecycle of orchard, possibly mediated through processes like depletion of weed seed banks or weed community filtering. Increased understanding of the broader contributions to ecosystem services, such as soil health and agroecosystem resilience, can enhance the benefit of cover crops and make them an attractive component of integrated orchard management systems.

Portions of this material are based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under agreement number G165-20-W7503 through the Western Region SARE program under project number GW19-194. USDA is an equal opportunity employer and service provider. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture. No conflicts of interest have been declared. The authors gratefully acknowledge Amélie Gaudin and Vivian Wauters for their critical feedback on these projects. We also acknowledge fieldwork support from Andres Contreras, Matthew Fatino, Guy Kyser, Guelta Laguerre, Katie Martin, and Seth Watkins. This research was conducted on lands that are the home of the Patwin people, who remain committed to the stewardship of this land.Vehicle electrification is currently considered one of the most attractive means of decarbonizing major segments of the transportation sector and can also directly contribute to improvements in urban air quality and public health. In spite of substantial progress and proactive policy support, the environmental impacts of electric vehicles under the wide range of future deployment scenarios are poorly understood. In certain intermediate-term scenarios where EVs reach a much larger share of the fleet and demand a double-digit share of available electric power , marginal CO2 intensity during EV charging times will typically be higher than annual average CO2 rates from the bulk power grid, upon which many current studies base their projections. On a 24-hour basis, this may be true for off-peak periods as well as certain peak periods . In certain conditions, even now, the average emissions assumption breaks down because of the high variability of generation requirements at the hourly or sub-hourly level in peak periods of the day or year. This research explores vehicle-grid interactions with a focus on environmental impacts for future scenarios in which electric vehicles are on a trajectory toward substantial market share . This project has leveraged and expanded a series of unique datasets and high-fidelity sub-system models that have previously stood alone as independent research contributions by the EVALUATE research team, its collaborators, and other researchers in the field. Those models govern vehicle energy consumption, travel demands, vehicle charging, and temporal emission profiles associated with electric power generation dispatch. Along with the expansion of those datasets and sub-system models, one of the most exciting contributions of this effort has been to develop an integrated methodology that enables high fidelity evaluation of emissions, in a systems-of-systems framework. An initial use case has been explored as a means of validating and tuning the methodology, which has generated some valuable insights in its own right. The scope of this work is initially based on a regional case study for a target vehicle classification . This convergence research has revealed important findings relative to the comparative emissions impact of light-duty vehicle charging during various times of day. Such findings may be valuable to an individual vehicle owner. For instance, under certain simulated scenarios, we observe marginal emissions can be as much as 20% lower in the overnight hours compared to marginal CO2 emissions experienced during an identical charging event during the daytime. This finding suggests that it will be essential to adjust and/or coordinate charging schedules to reduce the environmental impacts of EVs. More specifically, drying cannabis to the extent emissions impacts are prioritized among other objectives, individuals and policymakers should be encouraged or incentivized to charge when marginal emissions are lowest whenever possible.

This idea also has important implications for the location, type, and ownership models for tomorrow’s charging infrastructure. Translating and operationalizing this type of guidance will require some combination of education, access to rigorous and clear resources, signals between stakeholders , risk management analyses, and behavioral change. The study has also shed light on the critical nature of assumptions made for the dispatch of electricity generation to meet incremental new demand to charge vehicles. Several related observations are important to note and may be valuable for vehicle owners, researchers, and policymakers. First, our study is aimed at comparative analyses which provide insights into how a marginal assumption for CO2 emissions compares to other marginal assumptions, as well as to prevailing approaches . To our knowledge, this has not been done at this level of granularity. Second, in nearly all cases, marginal CO2 assumptions yield higher CO2 impacts than identical simulations that assume weighted average emissions. This variance is broad, ranging from 22% less to 97% greater, depending on a host of casesensitive factors. The team believes its ability to initially quantify and bound this variance represents an important contribution, as it helps decision-makers quantify how important various assumptions are. The research and its findings are provocative for additional reasons. Weighted average emissions in the U.S. are on a gradual decline, driven primarily by the retirement of coal and the addition of renewables over the past decade. This trend has favorable environmental impacts, because the retirement of high-intensity generation resources means they are less likely used to meet marginal demands, and similarly, the addition of low to no carbon-emitting resources has a commensurate impact on the weighted CO2 intensity of the overall grid. However, it is highly unusual for renewables to be used as the principal means of meeting marginal demand because they are generally considered non-dispatchable. This means grid operators will use fossil-generating resources as a means of meeting incremental load. Better foresight and energy storage are two areas that may eventually change this. On foresight, better awareness between stakeholders will help utilities predict and plan for EV charging events, which could presumably result in more holistic management of environmental impacts. Energy storage, at the moment, accounts for a very small fraction of total electrical demand, and it is therefore considered out of scope for the present study. Finally, despite encouraging trends in emissions for the bulk grid, the steady decline may plateau in the future for several reasons including: if transportation demands a large share of electricity, if costs to deliver electricity from zero to low carbon resources is substantially higher than conventional resources, or if additional electrification occurs at scale within other sectors . Still, by quantifying technical parameters related to both the magnitude and the range of possible emissions impacts as compared to multiple baselines , the study’s findings can be useful for education and awareness by all EV users. They also have clear implications on policy and public investment as mentioned, including the urgent need for managed and coordinated charging, and greater attention to resource planning, in terms of generation resources, dispatch decision-making, infrastructure funding, and the long-run environmental benefits and impacts for EVs across a range of use cases and time horizons. The report concludes with several suggestions for future work, including the need to leverage this methodology to consider grid characteristics relative to energy, emissions, decision-making, and planning out to 2030, and the capability of the tool to be scaled and more broadly adapted for conducting similar analyses in other regions.Vehicle electrification is currently considered one of the most attractive means of decarbonizing major segments of the transportation sector and can also directly contribute to improvements in urban air quality and public health. A key advantage of Electric Vehicles compared to internal combustion engine vehicles is that their carbon and emissions footprint is not fixed based on the vehicle technology from a given past model year, but instead can progressively improve in lockstep with a grid that is evolving toward a cleaner and lower carbon generating mix. Driven in part by policy, declining prices, and product availability, EV deployments are accelerating, having surpassed 1,600,000 total vehicles in the U.S. fleet by August 2020. Though EVs still account for less than 1% of the domestic vehicle fleet, this growth is notable compared to a near-zero baseline in 2010. Significant challenges have been overcome during this “first decade” of commercial adoption, including range limitations, charging infrastructure, total cost of ownership, and public acceptance.

We took the general approach of selecting the best, ecologically-relevant statistical models with Akaike information criterion , hydroponic rack system using ANOVA for global analysis, and finally using Fisher’s LSD for multiple comparisons For the field experiment, we tested various logical combinations of ecologically-relevant predictors with the aictab function from the AICcmodavg package . For both flowering timing and above ground biomass, the best model used just treatment and replicate as predictors, with no interactions. Then, we inspected ANOVA assumptions with qqPlot from the car package . One sample with extremely high biomass was removed as an outlier from the biomass dataset based on visual inspection of Q-Q plots. We proceeded with using the Anova function from the car package and the LSD.test function from agricolae .For the greenhouse experiment, we used the same general approach of using AIC to select models, ANOVA to compare predictors, and Fisher’s LSD for multiple comparisons. Some modifications were required to accommodate the factorial design and the structure of the dataset. The flowering timing data required a generalized linear model using a Poisson distribution with a log link function. Model comparison with AIC led us to select treatment, population, and replicate as predictors.

Relevant multiple comparisons were made with Fisher’s LSD using the glht functrion from the multcomp package . For the root:shoot biomass ratio data, we chose a multiway ANOVA that included treatment, population, replicate, and their interactions. Upon visual inspection of with Q-Q plots, three samples with very high root:shoot ratios were removed. Additionally, we removed 13 samples with indeterminate values . Multiple comparisons were made with emmeans and cld from multcomp. All figures were created with ggplot2 . We chose different kinds of figures for the field and potted plant experiments, due to the relative size and complexity of the potted plant experiment datasets.In the field experiment, weed management treatment did not affect field bindweed above ground biomass after 10 weeks of regrowth . The second replicate resulted in overall higher field bindweed biomass than the first and third replicates . However, time to flowering was affected by treatment . Broadcast glyphosate and tillage significantly increased time to flowering by one to two weeks on average compared to other treatments. Conversely, string trimming, glufosinate, glyphosate strips, and mowing resulted in shorter time to flowering, about five weeks on average after treatment application.

These four treatments delayed flowering one week compared to non-treated plots, suggesting that field bindweed flowering phenology is less sensitive to follow up treatment compared to the initial weed management treatment. Time to flowering is a critical trait for agricultural management which affects the ability of field bindweed to contribute to a persistent soil seedbank. Flowering delays of one to two weeks could be relevant for orchard weed management which is frequently constrained by logistical challenges, such as the availability of application equipment or prioritization of irrigation and other pest management operations. Furthermore, flowering timing could contribute to population-level shifts in field bindweed reproduction that affect fitness and lead to more clonal reproduction. These results indicate that disturbance through weed management can have complex effects on field bindweed even when above ground biomass is unaffected. Broadcast glyphosate application appears to be a useful management tool for delaying field bindweed regrowth and affecting the phenology of additions to the soil seedbank. However, we assume that sexual reproduction is positively correlated with above ground biomass, so this study does not support a link between these orchard weed management programs and the magnitude of soil seed bank additions . Future research should evaluate whether certain weed management practices, namely systemic herbicides, affect the relationship between biomass and seed production or viability. Additionally, future research should evaluate the intensity of longer sequential orchard management programs that are required to eliminate soil seed bank additions. The relative contribution of sexual and asexual reproduction to overall fitness remains an open question, and better general understanding of reproductive resource allocation could help us understand how various management programs might select for different reproductive and life history strategies over time.In the potted plant experiment, treatment , population , and replicate were all important predictors of root:shoot biomass ratio . Additionally, there were significant interactions between treatment and replicate and all three variables . In general, differences were subtle and effect sizes were small. However, the clipping treatment resulted in higher root:shoot ratios than the other treatments, which is logical given that shoot tissues had been removed from that treatment 10 weeks before plant tissues were collected. The field bindweed population sourced from an annual crop field generally produced higher root:shoot ratios than other populations, suggesting that this population produces relatively larger root reserves or less above ground biomass than the other populations from perennial and non-agricultural systems. Orchard managers should be aware of the possibility that field bindweed has the potential to reproduce differently between annual and perennial cropping systems or in the early stages following an environmental transition, such as during orchard establishment. Future research could evaluate the reliability of such differentiations and their potential contributions to field bindweed population change over time or changes in resource allocation that affect regrowth. Time to flowering in the potted plant experiment was affected by treatment and replicate and not significantly affected by population . In general, clipping and simulated tillage were similar to one another, and both delayed flowering compared to non-treated plants. The potted plants had different flowering phenology compared to the field experiment, with more variation in flowering timing. We attribute some of these differences to the controlled nature of potted plants, growing plants from transplants, and the subsampling design of the field experiment. Despite these differences, weed management disturbance in the potted plant experiment resulted in average flowering delays of one to two weeks, cannabis vertical grow system which is similar to the field experiment. Again, we argue that these delays can be practically important for orchard growers making decisions about management timing. Knowledge of weed reproduction and population ecology is essential for the implementation of integrated pest management programs. Furthermore, improved knowledge of the diverse and prolific reproductive methods of pernicious weeds like field bindweed can help us understand how weedy plants respond to various kinds of agricultural disturbance. These experiments demonstrate that flowering can be effectively delayed through common management practices.

Management practices that affect both root and shoot tissues, such as glyphosate and tillage, are especially effective at delaying field bindweed flowering under field conditions. This information could support integrated management of field bindweed that includes better scheduling of repeated management applications based on the development of field bindweed. Current orchard weed management programs in California frequently address field bindweed with repeated applications of glyphosate, and optimization of these applications could have sustainability benefits for agricultural landscapes in California and crop safety benefits in young orchards. Additionally, we present information that indicates differential reproductive characteristics between field bindweed collected from different home environments, suggesting the potential for an adaptive response to long term agricultural management programs. Weed populations that change in response to repeated management are a critical threat to agricultural productivity. This research reinforces the importance of planning and repeated management for developing integrated pest management programs that address the unique changes that affect orchards that are situated in complex California landscapes. Future research could account for the24hapiro24ve multi-year effects of disturbance on field bindweed reproduction, including consideration of perennial roots and asexual reproduction of established plants in controlled environments like potted plants or in different stages of the orchard life cycle.Cover cropping is a management strategy which adds potentially beneficial biodiversity to agroecosystems. Cover crops are non-harvested crop plants that cover soil that would typically be left bare under conventional agricultural management. Depending on specific cover crop management practices , farmers may leverage planned agrobiodiversity to enhance regulating ecosystem services , increase cropping system resilience , reduce agricultural externalities, and support sustainable intensification . Research has mainly addressed ecological impacts of annual cover crops grown in the fallow period between two annual cash crops but much remains to be known about impacts and potential in perennial systems where cover crops are grown on the ground beneath orchard trees with spatial separation from the main crop. Cover crops have known impacts on abiotic factors such as those related to soil structure or water use but more research is needed to understand broader biotic functions of horticultural importance. Aside from being practically important for orchard growers, weed suppression can indicate the absence of unfilled ecological niches within the orchard system . Whereas conventional orchards have significant unused resource pools that lead to the need for intensive vegetation control, cropping systems with diverse ground covers lead to regulation of water, light, nutrients, and safe germination sites so that these resources are less available for weed proliferation . An ideal orchard cover crop displaces weed plants with predictable, domesticated species that also provide additional sustainability benefits . Previous studies have demonstrated that cover crops can be useful in the unique environment of irrigated, perennial cropping systems in Mediterranean climates . In these systems, winter annual cover crops have a life cycle coincidental with winter rains as well as the dormant period of deciduous orchard crops. This phenology allows winter annual plants to have significant niche differentiation compared to the orchard crop while having niche overlap with important weedy species. Exploitative competition between cover crops and orchard weeds may be especially relevant given the long winter cover crop season and the cumulative effects of growing cover crops over multiple years. In contrast, other forms of interference, such as allelopathy or suppression of summer weed germination with cover crop residues , may be more important in annual cropping systems, where rapid changes in resource availability and fast life histories change the phenology of competition . Winter annual cover crops are therefore a practical way to use biodiversity in support of vegetation management in orchard systems, but it remains important to understand potential tradeoffs between ease of management and multifunctionality . Studies in unmanaged ecosystems highlight the potential role of diverse, multifunctional plant communities in increasing ecological functions and reducing weed invasability through niche differentiation and variation in developmental biology and phenotypic plasticity . However these patterns might not be reproducible in highly managed agricultural systems at scales relevant to populations, communities, and fields given increased disturbance and decreased species richness. . This study aims to fill a critical knowledge gap in understanding the potential of various multi-species cover crops for integrated pest management goals such as reductions in herbicide use in large-scale, intensified, and highly productive irrigated orchard systems in a unique, Mediterranean climate. We evaluated plant communities under two multi-species cover crop mixes, one that is functionally diverse and one that is functionally uniform, over two seasons in three commercial almond D.A. Webb) orchards in the Central Valley of California.

The large compositional shift strongly suggests that drought served as a catalyst to reset the communities. Drought often disrupts communities by reducing cover, lowering seed production, increasing thatch, and impacting the microbial community , and can make the community more susceptible to invasion if the current resident species cannot recover as quickly as recruiting species can establish . Both exotic annuals and native grasses are negatively impacted by drought , but in our experiment the annual noxious weeds were most affected. After the drought, we began to observe differences among each functional group in whether priority effects had truly disappeared or may have only not been observable due to low statistical power during the drought years. Priority effects among the two exotic annual grass groups completely disappeared and they reached co-existence, for each group’s cover was the same when planted alone, with each other, and where each recruited into the other’s priority plots. The loss of priority effects between the annuals may be attributed to a reduction in seed production during the multi-year drought, as decreased neighborhood propagule pressure can increase susceptibility to invasion , and as well as the reduction in decomposition since thatch build up can hinder germination . Both exotic groups, however, were able to suppress recruitment of the native perennials after the drought, as expected with their higher propagule pressure and competitive seedling dynamics, although not as successfully as before the drought.

Priority effects persisted in the system when natives were involved, with the strongest effects observed between the native perennial and noxious annual grasses, which share the later season-phenological niche. Each group continued to reduce cover of the other when seeded together and limited the other from recruiting into their monotypic seeded priority plots. However, while the role of phenology affected priority for both groups, the additional aspect of niche pre-emption of long-lived individuals resulted in stronger priority effects for the native perennials, which continuously kept noxious weed cover below 5%. The perennial deep-root system of the natives can limit soil moisture availability by using it early in the season and competing for residual moisture into the dry season. These results follow with the idea of limiting similarity, in that a species cannot invade if the niche is already occupied and that priority effects are stronger among species of similar functional groups . These principles are employed in restoration , and perennials are often planted to suppress grassland weeds . The ability of the native perennial grasses to consistently suppress noxious weed recruitment despite the drought was striking when compared to their contrasting lack of resistance to the naturalized exotic annuals. The sharp increase in naturalized exotics after the natives decreased in cover during the drought isn’t surprising, since native biomass is an important factor in preventing invasion , and niche pre-emption of perennials is dependent on individuals continuing in the same space overtime.

Naturalized exotic recruitment in the native monotypic priority plots could have negatively impacted the adult natives , which may explain why by the final year native cover was the same where planted alone and with the naturalized exotics. Regardless, native perennial cover increased to high levels when seeded, indicating that once individuals are established, they can persist among exotics, although they remain strongly seed limited . For natives, the importance of seedlings being given an extra year of priority before potential natural colonization of exotic annuals arose only during post-drought recovery, eight years into the experiment. In native priority plots, giving two years of priority resulted in greater cover than those given one year, as well as resulted in significant observable priority effects over being seeded with the noxious weeds for most of the post-drought recovery. Root establishment the first year is crucial to native seedling survival , and an extra year without competition for light and resources may have led to greater and deeper root biomass with greater below ground competitive ability . More root surface area to access available water likely leads to faster recovery post-drought . A quicker recovery post-disturbance would limit open opportunities for invasion . From a restoration standpoint, this suggests that an extra year of weed control may have long-lasting benefits to project success and add resiliency to future drought disturbance. Whether the changes we observed in the community composition would have still occurred without the drought is unknown and we cannot be certain about whether the strong priority effects would have lasted longer in less extreme conditions. Similarly, it is not clear if some of the weaker priority effects in the last couple years of monitoring are due to a weakening of priority effects over time, or variation in the strength of priority effects. Other long-term studies found that priority effects maintained lasting effects on the identity of the species present, but the communities converged in trait and functional diversity . A nine-year experiment on native vernal pool species showed strong initial priority effects between the seeded species, but could not comment on long-term dynamics, as an extreme wet year followed by a drought year led to dominance of a non-seeded exotic species across all plots .Our study has implications for management of annual grasses, which are increasingly common across many systems , Fynbos in South Africa . Late-season noxious weeds are invading naturalized exoticdominated rangelands, forming extensive monocultures of poor forage quality and causing economic and ecological harm . Our study suggests targeting noxious weed management during drought years as well as prioritizing native restoration alongthe invasion front . However, our results also confirm the necessity of weed control in the beginning of restoration as well as the need to manage for naturalize exotics after drought events. Overall, our study adds to the evidence that giving priority to native species can enhance their establishment , as well as suppress future invasions, vertical weed grow particularly when the natives and invasives share similar functional roles or phenological niches .Johnsongrass reaches 6 to 8 feet in height, with wide open, purplebrown panicles 4 to 20 inches long .

Stems and leaves are bright to deep green; leaves have a prominent white midvein and may reach 1 inch or more in width and 24 or more inches in length. Johnsongrass can reproduce via seed through self- or cross-fertilization and will reproduce vegetatively via a robust rhizome network. Johnsongrass establishes well in disturbed areas, rangelands, pastures, abandoned fields, and canals, as well as in virtually any cropping system. It thrives in moist environments, but due to its extensive rhizome system it can persist in drier topsoils if they are above high water tables. Johnsongrass may not be a significant threat to recovered areas with sufficient established vegetation, so avoiding disturbance in these areas is critical to preventing new or repeat infestations. Infestations usually begin in the margins of affected areas, but livestock and machinery may inadvertently spread seed to the interiors of fields, orchards, pastures, and other areas. Johnsongrass is an alternate host to Maize Dwarf Mosaic Virus , which affects corn , oats , millets such as pearl millet and foxtail millet , and sorghum . It also readily hybridizes with grain, forage, or sudangrass sorghums, which can reduce harvest quality due to contaminated seed.Since johnsongrass builds a substantial rhizome system in its first year, it can be very difficult to control once it is well established. Rhizome sprouts typically emerge early in the season and quickly reach full height, and they can easily outgrow and overtop desired plants. In addition, the extensive rhizome network can allow a single plant to be very competitive for water and nutrients over a substantial area. Significant crop yield reductions can be expected with acute johnsongrass infestation. For example, cotton can see a 20% yield reduction with as few as two tillers per square foot within rows . Corn without adequate control of johnsongrass can see yields reduced by up to 2 to 3 tons per acre . Additionally, disturbed portions of non-crop areas can quickly become dominated by thick stands of johnsongrass if management is not practiced.Johnsongrass can grow from seed or from overwintering rhizomes. Seed can germinate within a year and can remain viable for up to 6 years in the soil. Seedlings may form new rhizomes as early as the 5- to 6-leaf stage, about a month after emergence; buds of the new rhizomes may sprout the following year. Rhizome sprouting typically occurs in the early spring when daytime temperatures average above 60°F, but seed will germinate later, when daytime temperatures are about 70° to 75°F. Date ranges for rhizome and seedling emergence vary by region, but early to late March for warmer areas and late March to mid April for cooler areas are good approximations. Sprouts from new rhizomes grow more rapidly than from seed, but both grow quickly, and their development is essentially identical. Tillers usually appear at the 6-leaf stage, about a month after emergence. Flowering usually occurs 2 months from emergence and in California typically lasts from May to October, with each panicle producing up to 400 seed . The rhizome network later expands during seed ripening; individual plants can produce 200 to 300 feet of new rhizome growth per year . Above ground structures and older rhizomes die off over winter, but new rhizome growth persists and forms new sprouts the following spring. Because it can propagate via self-crossing and rhizomes, a single plant, if left undisturbed, can cause a significant infestation of up to 180 square feet in 2 years . Johnsongrass seedlings can resemble young corn seedlings, but because their seed remain attached, johnsongrass is easily discernable if plucked. The first leaf is usually parallel to the ground; early leaves have a smooth surface with no discernable midrib and smooth edges. A white midvein may begin to show at the leaf base of seedlings. Seedling collars are usually pale green to whitish, and sheaths may begin to take on a red-purple tinge as the plant matures.In California, johnsongrass can be as much as 8 feet tall at maturity . Stems grow from the crown, are erect and unjointed at the nodes, and may have a red-purple base or tinted internode. Nodes may have some fine hairs, but internodes are usually smooth. Prop roots may form near the base of stems . The leaves are rolled in the bud, generally emerge flat, and have a prominent midrib, especially at the base . Mature leaves are hairless to nearly hairless and may have slightly rough edges, with a prominent fringed ligule up to 0.2 inch long or more . Sparse hairs may be present on the leaf or sheath near the collar. Inflorescences form as large, open panicles that are pyramidal or conical in shape. Spikelets can range from pale green or gray to golden to purple-brown. They may remain on the panicle or shatter into pairs or trios that consist of a lower fertile spikelet and one or two sterile upper spikelets.

A majority of the runoff was collected during Decemberand January for the 2002-2003 and 2004-2005 winters, and February for the 2003-2004 winter. Cumulative runoff collected from individual plots during the three winters ranged from 0.02% to 3% of seasonal rainfall. Runoff was usually collected during rain events greater than 1 inch per day. Runoff was highest during the second and third years of the trial. During three consecutive winters, runoff was significantly lower in the covercrop treatments . ‘Trios 102’ triticale and ‘Merced’ rye had significantly less runoff than the bare treatment . Suspended sediment and turbidity were also significantly lower in runoff collected from the cover-crop treatments than in bare middles during winter 2004, but nutrient levels were similar among all treatments .Vines. Weed control and cover treatments did not have any significant effect on the nutritional status of the grape vines as measured by nutrient levels of the leaf petiole tissues, as determined by ANOVA. Although the nutrient levels by year were significantly different, the interactions of weed control-by-cover and weed control-bycover-by-year were not significant . Weed control and cover treatment also had no significant effect on blade nutrient content with the exception of boron and phosphate content. Vines adjacent to cover crops had significantly lower boron and phosphate levels in the leaf blade tissue than vines adjacent to bare row middles.

As with the petioles, there was an absence of significance between the interaction of weed control-by-cover and weed control-by-cover-by-year for all nutrients analyzed .Soil cores indicated that most of the vine roots at this site were located under the vine row and few of the roots extended out to the row middles. This root distribution probably occurred because irrigation water was applied under the vines, and low rainfall at the site does not facilitate root growth into row middles. Thus, the lower nutrient levels in vines near cover crops may have been accentuated by irrigation effects that reduced vine root exploration of the soil to a narrow band under the vines. Since cover-crop roots probably grew into this zone there may have been competition between vines and cover crops for some nutrients. Soil. Cultivated rows had significantly lower levels of nitrate-nitrogen . Although the nutrient levels by year were significantly different, there was an absence of significance between the interaction of weed control-by-cover and weed control-by-cover-by-year . The differences observed in nitrate-nitrogen in the cultivation treatment may be due to the impact of loosening soil on water movement and leaching. Weed control treatments had occasional impacts on soil mineral nutrition in the middles, but results were inconsistent from year to year .

The most significant impacts of the vineyard floor treatments were of the cover-crop treatments on soil parameters in the middles. Soil organic matter in cover-cropped middles was higher than in bare middles each year . Cover crops affected key soil nutrients in the middles; for instance, cover crops greatly reduced nitrate-nitrogen , and to a lesser extent, extractable phosphorus , which may be beneficial in reducing loss of these nutrients in runoff during winter storms, but which also may have reduced the phosphorus content in the vines. In addition, cover crops in the middles also significantly reduced soil boron , extractable sodium and pH , and increased chloride and zinc when compared to bare soil.Soil microbial biomass. Microbial biomass varied as a result of both the cover-crop and weed control treatments. In both the middles and vine rows, microbial biomass was higher in rye cover-crop plots compared to bare plots . These results confirm earlier observations by Ingels et al. that microbial biomass carbon was higher in cover-cropped middles compared to bare middles. In the vine rows, microbial biomass was greater in plots adjacent to rye cover-cropped plots compared to bare plots. The effect of cover crops grown in the middles on soil in the vine rows may be due to cover-crop roots or tops extending into the vine rows and their subsequent decomposition, providing a food source for soil microbes. Microbial biomass varied between the weed treatments in the vine rows but not middles . In the vine rows, microbial biomass was significantly higher in the cultivation plots compared to the pre-emergence weed control plots . The most likely explanation is the incorporation of greater amounts of weed-derived carbon into the surface soil of the cultivated plots. Mycorrhizae. AMF can benefit grapevines by improving the nutritional 35 30 25 20 15 10 5 0 Cultivation Post-emergence Pre-emergence herbicide herbicide Bare ground Merced rye Trios 102 status of the plant and producing a highly branched root system. We quantified AMF reproductive structures in grapevine roots to determine if the weed control treatments in the rows and/or cover-crop treatments in the middles had significant effects on mycorrhizal colonization from 2003 through 2005. Based on ANOVA, the effects of weed control on colonization were not consistent among covercrop treatments . Grapevines adjacent to ‘Merced’ rye had higher colonization compared to those adjacent to ‘Trios 102’ triticale or bare ground, in both the cultivation and pre-emergence treatments . In contrast, grapevines in the postemergence treatment had the lowest colonization when adjacent to ‘Merced’ rye. These findings were consistent in each study year, based on the absence of significant main or interactive effects of time . It is possible that low colonization of grapevines in the post-emergence-by-‘Merced’ rye treatment is associated with this treatment’s weed community. Indeed, weed species vary in their ability to host AMF , so their presence or absence may affect mycorrhizal colonization of grapevines. Indeed, reports on the influence of plant community composition on AMF suggest that plant diversity has a strong effect on AMF diversity , and this may affect the colonization of individual plant species.All yield, fruit quality and vine growth parameters varied by year, and this was the only significant effect for these parameters, vertical farming racks with the exception of berry weight and titratable acidity . No differences in crop yield or fruit composition were observed from 2001 to 2005 due to weed control treatments . Cover-crop treatments also had no significant effect on yield or fruit composition, although in 2001 and 2004, there was a reduction in berry size in the ‘Trios 102’ triticale treatment. Weed control treatments also had no effect on vine growth , based on shoot counts and pruning weights taken at dormancy. Cover-crop treatments had no significant effect on vine growth when averaged over 5 years, although in 2001 and 2005 the ‘Trios 102’ triticale treatment significantly reduced pruning weights. The trend for lower pruning weights may be related to the greater decline in soil moisture in the middles where this cover crop was used.

It appears that vine growth, yield and grape quality are more significantly affected by annual precipitation than by vineyard floor management practices.In low rainfall areas the choice of cover crop is critical because of its effect on available soil moisture. We observed that late-maturing ‘Trios 102’ used more soil moisture during the vine growing season; if irrigation water does not compensate for water used by the cover crop, reduced vine growth and yield losses may result. The clear benefits of cover crops were increased organic matter in the middles and reduced sediment loss. Microbial biomass was increased in cover-cropped middles and there were indications that this effect extended to under the vines. Although there were no negative impacts of weed control treatments on vine productivity, we observed increased compaction over time from the use of cultivation. This study indicated that the choice of weed control strategy and cover crop must be carefully considered to maximize the benefits and minimize negative impacts of the practices. The benefits of cover crops are concentrated in the middles,and future research should focus on evaluating practices that improve the quality of soil under the vines.Understanding the drivers of plant community composition is increasingly critical as many ecosystems face novel species interactions due to invasion and global change. Plant-soil feedbacks can impact plant neighbor interactions and drive legacy effects of former plant communities on current community composition . Plants can change soil physical, chemical and/or biological properties, which can impact plant growth or fitness, and thus the trajectory of the community . A large body of scholarship demonstrates the existence of PSFs but there are still key gaps in our understanding of how important they are, relative to other drivers of plant community composition, and thus, many have called for investigating the role of PSFs in long-term field settings that incorporate competition at the community level . Recent studies demonstrate that plant-soil feedbacks may be dependent on the length of the experiment, and often differ in field settings compared to greenhouse conditions . Short conditioning phases may over-emphasize the role of microbial communities and nitrogen cycling and miss the impacts of longer-term changes to soil organic matter and water holding capacity . Similarly, short feedback phases can fail to capture the impact of annual variation in environmental conditions or how feedbacks can develop over time . Further, in variable field environments, it may be important to not only consider surface soil, but also plant impacts on subsurface soil. Similarly, it may be important to go beyond a focus on above ground biomass as an indicator of feedback, instead assessing multiple traits across multiple life stages . There is particular interest in the scientific and management communities in understanding how plant-soil feedbacks may mediate interactions between invasive and native plant species. PSF studies have shown that native plants tend to have negative feedbacks, often through accumulation of pathogens decreasing native plant performance. This negative feedback likely drives plant co-existence and diversity . In contrast, invasive plants can shift microbial community composition and physical and chemical properties to benefit themselves , sometimes to the detriment of native growth . This suggests that successful restoration of natives into invaded sites may require an initial step of restoration of soil conditions. Both inter- and intra- specific plant competition influence the overall importance of PSFs in natural communities. Direct competitive interactions among plants are known to interact with or be additive to plant-soil feedbacks . For example, feedbacks impacting a weaker competitor’s performance may be overwhelmed by competition from a stronger neighbor or feedbacks negatively impacting a stronger competitor may allow co-existence of the weaker species . By assessing feedbacks on plants growing in a community instead of neighbor-less plant individuals, we can better evaluate their relevance in a natural setting .We use multiple plant performance variables to assess the importance of PSFs in California grasslands with a long-term field experiment using mixed communities composed of native and/or exotic species. These grasslands are heavily invaded with exotic annual grasses and forbs, with the loss of natives occurring more than 300 years ago .