Decisions related to seed depth will vary depending on soil type, seed size, and weather and soil conditions at the time of planting. Because of the challenges associated with planting to moisture,less experienced growers may opt to irrigate up their newly planted squash seed. This practice is effective and will ensure a good stand, but results in more weed competition and management costs. Please see the publication Tillage, Bed Formation, and Planting to Moisture in this Grower Guide series for additional details.Drip irrigation minimizes weed pressure, although some growers use overhead irrigation prior to fruit set to help control powdery mildew. Timing of the first drip irrigation depends on the waterholding capacity of the soil, the initial soil preparation, the amount of winter rainfall, and the amount and timing of any pre-irrigation. Lay out drip lines when the plants have been thinned but are still small, and the first cultivation is complete . To minimize weed pressure, the first irrigation ideally would take place once squash leaves grow a full canopy to shade out weeds that may emerge once irrigation is initiated. From this point on, vertical growing weed use evapotranspiration estimates from your local CIMIS station or another source to inform irrigation decisions. Irrigation rates will likely range from 1–2” per week for the duration of the crop’s development.
Once the squash fruits are sized there is no need for further irrigation and the water can be cut.When squash seeds are planted to moisture, late season rains are minimal, and drip irrigation can be delayed until there is a full canopy of leaves between plants within the row, there may be no weeding necessary during the entire cropping cycle. This type of management can significantly reduce production costs, keep the field clean of unnecessary weed seed, and maintain profitability. If between-row weed management is needed after thinning and in-row weeding, use a three-bar cultivator mounted with disc hillers, sweeps, and knives. Because of the low growing point of squash plants, it is not advisable to move soil towards the plant following emergence. Rolling cultivators are therefore not an appropriate tool to effectively manage weeds in winter squash. Run shallow chisels behind the tractor tires to break tractor tire wheel compaction, especially in situations where soil moisture is high at the time of cultivation. This will aid fall tillage and minimize clod formation. Generally, only one or two cultivations are needed for weed management in winter squash. The few weeds that escape cultivation can be hand pulled once the squash is in full bloom. After that, the canopy should prevent further weed germination or growth . Additional passes may be needed to control bindweed or other perennial weeds.Color is probably the best indicator of harvest timing.
Most varieties will develop a deep color as the stems dry down, the rind loses its sheen, and the fruit hardens. For example, Butternut will go from light green to deep tan; Sweet Dumpling and Delicata will go from white/green to deep yellow/orange Once the squash foliage has fully senesced, cut the squash from the vine with hand-held clippers, leaving a short stalk on the fruit. Take care not to break off the stem as early post-harvest decay can develop at the point of detachment. Windrow the harvested squash in the field to facilitate pick up after curing . Field curing—leaving squash in the sun for 1–2 two weeks — allows fruit to shed some moisture, concentrates sugars, hardens the skin, and slows respiration, allowing for better long term storage. Curing for more than two weeks may cause sunburn and make fruit susceptible to insect damage. If rain or a heat wave is forecast, squash should be picked up and stored. Cardboard bins may be used for field removal and temporary storage. Handle squash carefully to avoid cutting or bruising the skin. Remove dirt from squash and cull damaged fruit while filling bins; do final quality assessment and grading when packing boxes from the bins for market. Bins on pallets may be moved with a three-point forklift attachment on a tractor, or a forklift. Store squash in a shady, covered area.Shortly after harvest, retrieve all drip lines and prepare the ground for a subsequent cash crop or winter cover crop. Mow the squash vines after harvest to eliminate large clumps of plant material prior to discing. If left intact, large vine pieces can cause “wrapping” and “gathering” problems with some follow-up tillage implements . Because squash requires minimal tractor and foot traffic on moist ground during the cropping cycle, the soil should be easy to work following harvest.
Typically the winter squash field will only need mowing and one or two passes with a disc to adequately prepare the ground for planting. Optimal soil conditions support good cover crop stands and rainwater infiltration rates.Like other plant viruses, geminiviruses encode 6-8 multifunctional proteins that are involved in replication and gene expression, encapsidation, movement and suppression of host defenses . Once viral DNA enters the plant cell nucleus, the Rep protein is expressed to initiate replication of the viral genome, which occurs through double-stranded DNA replicative intermediates by a combination of rolling circle replication and recombination-dependent replication . The transcriptional activator protein regulates the expression of vsense transcripts, and interferes with TGS and PTGS . The replication enhancer protein enhances geminivirus DNA accumulation, whereas the C4 of some geminiviruses suppress PTGS. The capsid protein forms the geminivirus virion and is the determinant of insect vector specificity . The CP of monopartite begomovirus also functions as a nuclear shuttle protein and mediates the nuclear export of the viral genome . The V2 or pre-coat protein of some begomoviruses suppresses PTGS and mediates the movement of monopartite geminiviruses . Finally, bipartite geminiviruses also encode movement proteins, which regulate viral movement into and out of the nucleus and cell-to cell through plasmodesmata .Some geminiviruses can be associated with circular ssDNAs referred as satellites. Two main classes of satellite DNAs have been described in association with these viruses: alphasatellites and betasatellites . The genome size of alphasatellites and betasatellites is ~1.4 kb, which is about half the size of the begomovirus genome, and these satellites share little sequence identity with the helper virus, with the exception of the conserved stem-loop structure that is required for RCR . These satellites depend on their helper virus for replication and encapsidation, movement and insect transmission . Interestingly, these satellites are promiscuous with respect to helper virus replication with many satellites trans-replicated by multiple begomovirus species .Alphasatellites replicate their genome through a Rep-like protein , which is similar to Rep proteins of nanoviruses . These satellites are strictly dependent on their helper virus for movement, encapsidation and insect vector transmission . Alphasatellites are mostly associated with monopartite begomoviruses in the OW . However, these satellites have also been found in association with bipartite begomoviruses in the NW , and most recently, in association with a betasatellite and a mastrevirus in the OW . Betasatellites also occur mostly in the OW and are usually, but not exclusively, associated with monopartite begomoviruses . Unlike alphasatellites, betasatellites do not encode a Rep-like protein. Thus, they depend completely on the helper virus for replication as well for encapsidation and whitefly transmission .
Instead, these satellites encode the βC1 protein, which is a major pathogenicity and symptom determinant that interferes with TGS and PTGS . In 1997, a type class of satellite DNAs was first described . These satellites were associated with some bipartite begomovirus in the NW and some monopartite begomoviruses in the NW and OW , and they were named deltasatellites. The genome size of deltasatellites is ~0.7 kb , and has sequence and structural similarities with betasatellites . However, deltasatellites do not encodes anyknown proteins and share no sequence identity with the helper virus . In general, growing rack deltasatellites do not seems to have a role in pathogenicity and symptom development, but in some cases , these satellites can interfere with virus DNA accumulation .Geminiviruses have a long evolutionary history, likely having evolved from ancient phytoplasmal-type II extrachromosomal ssDNA plasmids via acquisition of CP genes from an RNA virus . Several lines of evidence support this hypothesis. First, the existence of prokaryotic-like features in the genome of present-day geminiviruses, e.g., the promoter of the tomato golden mosaic virus CP is active in Escherichia coli, begomovirus ssDNA and replicative dsDNA forms have been found in plastids, and geminiviruses can be replicated in Agrobacterium tumefaciens . Second, structural modeling of the geminiviral CP showed homology with that of icosahedral RNA viruses . Third, the presence of conserved amino acids motifs in the Reps of geminiviruses and ss DNA plasmids of Gram-positive bacteria . Together, these findings provided strong evidence for the evolution of geminiviruses from ancient prokaryotic DNA plasmids following recombination with an RNA virus. However, this hypothesis involves the occurrence of a rare DNA/RNA recombination event in different cell compartments . Another hypothesis is that geminiviruses emerged following recombination between an ancient ssDNA virus encoding a RCR-like Rep and a marine virus . Evidence supporting this latter hypothesis came from: sequence and phylogenetic analyses showing that the type II EcDNA encoded Rep is not of bacteria origin but has been acquired by phytoplasmas from an ancient Rep-encoding virus, and metagenomic data analyses have shown aa sequence similarities between the CP of geminiviruses and that of viruses from soil or marine environments . Although the precise origin of geminiviruses cannot be determined with complete certainty, the evolution of geminiviruses must surely have involved the acquisition and modification of additional genes required for host infection and insect vector transmission . In this scenario, these viruses have co-evolved with plants for millions of years, i.e., well before the occurrence of continental drift . The subsequent diversification and evolution of geminiviruses was mediated by viral genetic mechanisms such mutation, recombination and, in the case of the bipartite genome, pseudorecombination . Moreover, these events have ocurred multiple times in different geographic regions, giving rise to multiple viruses that infect different hosts . Geminivirus cause economically important diseases of food, feed, and fiber crops worldwide , and these diseases have resulted in substantial losses to agriculture, especially in tropical and subtropical regions . Moreover, the increase local populations and long distance spread to new regions of insect vectors, especially the polyphagous whitefly supervector, have accelerated the emergence of new geminiviruses in different geographical regions. The resulting diseases have caused substantial losses to economically important crops, including common bean, cassava, cotton, cucurbits, pepper, tomato and ornamental plants.Viruses in the genus Begomovirus infect dicotyledonous crops and cause economically important diseases in tropical and subtropical regions of the world. There are >422 begomovirus species officially recognized by the International Committee on Taxonomy on Viruses , making this one the largest and most diverse genera of viruses . Begomoviruses infect a wide range of dicotyledonous crops and are transmitted by whiteflies of the Bemisia tabaci cryptic species complex . The complex is formed by at least 34 morphologically indistinguishable species, which have different biological and molecular properties . For example, B. tabaci Middle East-Asia Minor 1 and Mediterranean are highly polyphagous, rapidly develop insecticide resistance, and are highly fecund. Moreover, transmission efficiency varies among species, depending on the nature of the virus-host combination . In general, the mode of insect transmission of begomoviruses is circulative and non-propagative . However, results of some studies have shown that the invasive monopartite tomato yellow leaf curl virus replicates in cells of the primary salivary glands of the whitefly adult, and that such replication requires the interaction of Rep with the whitefly DNA polymerase δ and proliferating cell nuclear antigen . Moreover, TYLCV can also be transmitted transovarially for at least two generations of whiteflies . Thus,it seems that there is at least one species of begomoviruses that have evolved to replicate in the whitefly vector, and that, this replication may only happen under certain conditions .The begomovirus genome is either monopartite, with a single genomic DNA of ~2.8 kb; or bipartite, with two DNA components of ~2.6 kb, designated as DNA-A and DNA-B . The DNA-A and DNA-B components share no sequence identity, except for an ~200 nucleotide noncoding conserved sequence known as the common region , which encodes the ori and regulatory sequences .