Sulfosulfuron is registered in California under the trade name Outrider for non-crop use. Imazapic is not currently registered in California and faces a difficult registration pathway in California, so future research will focus on another imidazolinone herbicide, imazamox, which has a more favorable registration pathway. Crop safety studies will need to be repeated using chemigated imazamox and will be conducted in 2021. Rotational Crop Safety Evaluation Based on this initial rotational crop safety experiment, there were few indications of problems related to the imidazolinone herbicides applied five times via chemigation at the proposed 2x use rate. There was some early season stunting and chlorosis observed with sulfosulfuron in sunflower, but the plants grew out of this injury. There were some indications of crop safety concerns for PPI sulfosulfuron treatments, primarily for corn and melon. Seeding across all crops was inconsistent and denser than commercially planted stands. The field was treated with rimsulfuron before planting corn, safflower, sunflower, beans, and melon. Rimsulfuron is not registered on melons, so differences in melon plant height and weight cannot be attributed solely to PICKIT herbicide treatments. Heavy field bindweed and gopher pressure also contributed to the variability within and among treatments. If the herbicides utilized in the PICKIT system are registered in California, vertical growing racks tomato growers will have to adjust crop rotationsbased on the plant back restrictions associated with sulfosulfuron .
Given the importance of tomato in this cropping system, such rotational crop restrictions might be acceptable to growers impacted by branched broomrape. Only a single rotational study was conducted, and more experiments should be conducted to further inform growers and the industry of the specific crop safety concerns with this broomrape management approach. PICKIT Efficacy Evaluation Currently, the economic and action threshold for branched broomrape in California is any detection of the parasitic plant. With the exception of a single plot, all of the treatment plots had broomrape . The PICKIT treatment plots had fewer broomrape clusters on average than non-PICKIT plots, though the late season foliar applied treatments should not have had affected early season emergence and had some of the lowest cumulative number of broomrape clusters . This is likely due to an uneven distribution of broomrape, resulting in some “hot” areas of the field with high broomrape emergence and “cold” areas with relatively low emergence. The experimental blocking was arranged based on reports of higher broomrape density observed by the grower the previous year in the south edge of the field. However, likely due to cultivation patterns, there were some areas of some beds with lower or higher broomrape density than adjacent beds. While the experiment was blocked to reduce variation due to factors like this, more experiments must be done to determine the efficacy of each individual treatment.
Broomrape locations were mapped with GPS in 2020, and this mapping data will be used in subsequent experiments at this location to inform blocking decisions . PICKIT treatments had some effect on broomrape emergence, generally reducing emergence compared to non-PICKIT treatments. However, more studies will need to be conducted to determine the relative efficacy of individual PICKIT treatments among each other and to further refine rates and treatment protocols for control of branched broomrape. The PICKIT decision support system is based on a growing degree day model developed using Egyptian broomrape . It has been noted by PICKIT researchers that branched broomrape and Egyptian broomrape do not share the exact same phenology . Future research will examine the effects of alternate timing of chemigation treatments to address the temporal difference in development between the two species.Further research on branched broomrape control strategies in California processing tomato will continue. Due to the difficult regulatory pathway for imazapic in California, future research will focus on imazamox, which already has a registration in California on alfalfa . A project was initiated in early 2021 in Chile to evaluate the potential of imazamox as a chemigation herbicide in addition to informing decisions for mid-2021 research in California. As of summer of 2021, there have been several additional formal reports of broomrape infested commercial tomato fields. The problem is growing, and while eradication may still remain the goal for many, management tools will need to be developed if this weed were to become widespread and or de-regulated as a quarantine pest.
The seeds of many weed species can remain viable after passing through the digestive tract of livestock. The dungs and manures of different species of livestock have been found to contain a variable number of viable weed seeds, which makes livestock a major agent of weed seeds dispersal in both grazing and non-grazing systems.Dairy manure, commonly applied in croplands either directly or as a compost can be contaminated with weed seeds and thus can result in further escalation of weeds in farms. With the current increase in the adaptation of organic production systems, weed infestations through livestock are expected to become greater than in the past, as these systems are largely reliant on the use of organic amendments such as manure. Indeed, weeds are known to be a major constraint to the productivity of organic farms. Infestations caused by manure applications can be highly variable because seed recovery and viability after digestion vary considerably depending on the livestock type, feed and plant species. For example, physical damage to seeds depends on the degree of mastication, which varies among livestock species. Sheep and goats exert more damage to the seed than cattle do, and feed properties including forage/concentrate ratio, particle size, quantity and digestibility can affect seed viability and recovery though changes in rumen microbial population, ruminal pH and the passage rate of rumen fluid. For example, seed recovery for highly digestible feed was higher than less digestible feed due to a marked reduction in the retention time in the rumen/digestion tract. Seed properties such as the hardness of seed coat, seed size, shape and specific gravity are important to the survival of seeds passing through the digestive tract of livestock. Small-round seeds with smooth exteriors, seeds with high specific gravity and impermeable seeds typically have high recovery and survival. Previous studies have focused on grazing livestock and pasture plant species, however, only a few studies have examined the fate of weed seeds under non-grazed systems. Previous studies have shown that the dispersibility of seeds varies among different animals yet whether different cattle types within the same species can cause differential weed seed fate is poorly understood. The most popular milk-producing dairy cattle breed globally is the Holstein-Friesian, which are classified into four major groups: 1- lactating cows, 2- feedlot male calves, 3- dry cows, and 4- growing heifers. As these cattle groups vary in physiological properties of their digestive tract and receive different daily diets, we hypothesized that the fate of weed seeds, measured in terms of recovery and viability, growing racks will depend on the cattle type. We tested this hypothesis using four weed species: Cuscuta campestris Yuncker., Polygonum aviculare L., Sorghum halepense Pers, and Rumex crispus L. These weed species are common in crops from where the cattle feeds are sourced and they also vary in seed properties. The use of weeds with contrasting seed properties could allow us to examine the association between seed traits and the propensity to survive the digestive tract.
The seeds of four weed species were collected at maturity from infested fields in Karaj, Iran in early September 2009 . The selected species are amongst the most abundant weed species in the crops which are utilized to produce the livestock feed in many regions of Iran. The seeds were cleaned by hand and stored indoor for two weeks until used in the experiment. The species vary in seed dimension, weight and specific gravity as shown in Table 1. Prior to seed feeding study, to test initial seed viability, four replicates of 25 seeds from each weed species were placed on a Whatman No. 2 filter paper moistened with 5 mL of distilled water, in an 8.0 cm diameter Petri dish. Dishes were incubated for 14 d at temperatures and photoperiod conditions optimal for the germination of individual weed species: these were 30°C with an 8 h photoperiod for C. campestris, 20 /10°C with a 8 h photoperiod for P. aviculare, 25°C in continuous darkness for R. crispus, and 30°C in continuous darkness for S. halepense. At the end of the germination assay, the viability of nongerminated seeds was examined using a tetrazolium chloride test, whereby the seed coat was scarified with a scalpel to expose the embryo to 2.0% 2,3,5-triphenyl tetrazolium chloride solution , pH 7.0, for 48 h at 20°C. Seeds stained red were regarded alive and were counted. The number of viable seeds was calculated as the sum of seeds that had germinated and non-germinated seeds with TZ solution-stained embryos.The seed-feeding study was performed in the Animal Science Research Station of the University of Tehran in October 2009, to quantify seed recovery and seed viability in four different Holstein cattle groups: 1- lactating cows , 2- feedlot male calves , 3- dry cows , and 4- growing heifers . Department of Animal Science in University of Tehran is responsible for all studies performed in the Research Station. The seed sampling did not involve endangered or protected species. Animals were cared for in accordance with the guidelines of the Iranian Council on Animal Care. All sampling procedures were performed without any stress to the animals. Four individuals from each of the groups were housed in individual tie stalls for 15 d. The cattle were acclimatized in their stalls for 10 days before five days of seed-feeding began. All cattle groups were fed according to the recommendations of the Nutrient Requirements of Dairy Cattle as shown in Table 2. The lactating cows and feedlot male calves were fed twice daily at 0700 and 1530 ad libitum, but feeding times were restricted for dry cows and growing heifers. All cattle groups received continual access to water. On the 11th day, the seeds of four weed species were mixed with 0.5 kg aromatic calf concentrate and sugar beet molasses, and then fed as a supplement to each animal. For each weed species, 1500 seeds per kg of feed was added to the cattle diets. Based on the amount of feed given to each group , the total number of seeds fed were 120000, 60000, 60000, and 72000 seeds for lactating cows, dry cows, growing heifers, and feedlot male calves, respectively. Total dung output for each animal was collected and weighed every 24 h for four consecutive days. One kg of the daily homogenized excretion was randomly sampled for seed recovery and viability testing. An additional sample of daily dung output was oven dried at 68˚C for 48 h and weighed to determine the dry matter content. The pH of ruminal fluid was measured on the 14th d of trials at 0700 am before the morning meal, by taking 50 mL of rumen fluid from the ventral sac using a vacuum pump. Ruminal pH was measured immediately after sampling using a portable pH meter .All main effects and their interactions were significant for seed recovery . Total seed recovery for all weed species was lowest in dry cows and never exceeded 45%. The highest percent recovery was observed with lactating cows with the only exception of R. crispus . For this species, seed recovery was consistently low regardless of the cattle type as opposed to S. halepense, which exhibited a high percent recovery particularly when fed to lactating cows . Analysis of within Holstein cattle group showed that seed recovery dose not vary among weed species in the dry cows and growing heifers . No significant difference was observed, averaged over cattle types, between the total seed recovery of P. aviculare and S. halepense. The recovery time , as inferred from the parameter tR50 , varied from 25 h in lactating cows for C. campestris, to 51 h in dry cows for S. halepense . Recovery time varied across cattle types in a similar manner to that of the percent seed recovery, whereby dry cows had the slowest passage rate, while lactating cows had the fastest passage rate. That is, the recovery time for dry cows was approximately twice as long as that of lactating cows. Other cattle types, growing heifers and feedlot male calves, were intermediate in this respect.