Spinach is susceptible to weed pressure because it is produced on high-density 80-inch wide beds with 18 to 42 seedlines. There is no opportunity to cultivate the bed top so all weed control is accomplished by managing weeds in prior rotations, cultural practices, chemical weed control or hand weeding. Clipped spinach is mechanically harvested and must be kept as weed free as possible to reduce hand weeding costs. In the recent UC publication, Sample costs to produce and harvest organic spinach (Tourte et al, 2015 http://coststudies.ucdavis.edu/current/ ) hand weeding costs averaged $440 per acre. However, weeding costs can easily exceed $1,000 per acre in weedy fields, and if cost get to high, growers may decide to disc the field. A key factor that affects weeding pressure in spinach fields is the prior crop. Long-season crops such as peppers, annual artichokes and leeks tend to allow more weed seed set and can increase weeding costs in a subsequent crop like spinach.
RoNeet and Dual Magnum are registered preemergent herbicides for use on spinach. RoNeet is the most commonly used preemergent herbicide on spinach; it is volatile and must be quickly incorporated into the soil for best efficacy. Post planting, preemergent applications are typically incorporated with sprinkler irrigation, but it can also be mechanically incorporated prior to planting. It has a 48 hour reentry interval following application. RoNeet controls problematic weeds such as malva, purslane, lambsquarters and pigweed.
Dual Magnum provides control of weeds such as burning nettle. One difficulty with the use of this material is that it has a 50 day preharvest interval (PHI). This PHI often necessitates making applications prior to planting clipped spinach which matures in 25-35 days during the summer production season.
Over the past three years we have evaluated Spin-Aid for use in clipped spinach. Spin-Aid is registered for use on processing spinach and has a 21 day preharvest interval (PHI); this use pattern fits the production practices for freezer spinach. However, washing and bagging spinach is also considered processing and would allow its use for clipped spinach. During the summer months, clipped spinach matures in 25-30 days which makes complying with the 21 day preharvest interval difficult. The first opportunity to apply Spin-Aid typically occurs following the germination water at about 8-10 days after planting which makes complying with the 21-day PHI difficult in many situations. Spin-Aid has various warnings on the label regarding phytotoxicity or potential delay of development under some conditions; this is a concern for a rapidly developing crop like clipped spinach. Research conducted a number of years ago indicated that phytotoxicity by phenmedipham was made worse under warm temperatures. As a result, the label stipulates that temperatures >75 °F can cause crop injury. Research carried out by Ran Lati indicated that high light conditions reduced the tolerance of phenmedipham more than temperature in the coastal production district. Given this observation we evaluated the impact of nighttime vs daytime applications of low rates of Spin-Aid (0.5, 1.0 and 2.0 pints/A) for use on clipped spinach.
Research consisted of making morning (high light) and evening (low light) applications of Spin-Aid nine days after seeding when the 1st true leaves were <1/4 inch in size. We observed less phytotoxicity from evening than morning applications (Table 1). Damage to spinach was most significant in morning applications of 2 pint/A Spin-Aid and consisted of necrosis on the tips of some cotyledons (Photo 1); these symptoms were not seen in the 2.0 pint/A evening applications (Photo 2). The 0.5 and 1.0 pint/A rates had acceptable levels of phytotoxicity regardless of application timing. Spin-Aid did not significantly reduce the number of malva plants but stunted them (Photo 3) making them less problematic during harvest as is the case of untreated malva (Photo 4). Nettleleaf goosefoot was susceptible to Spin-Aid and all rates significantly reduced the population of this weed. Commercial-scale trials were carried out in fields that had high populations of weeds. At one site Spin-Aid reduced the number of purslane, shepherd's purse and hairy nightshade by half (Table 2). The overall yield of the standard treatment was 11.007 tons/A and the 1.0 pint/A Spin-Aid treatment was 10.061 tons/A indicating that there may be some yield reduction with the use of Spin-Aid.
The results from these and other trials look promising, but modifications to the current label will be necessary and we are currently working with the manufacturer, Engage Agro, to see if that will be possible. If successful, this will provide a powerful tool to reduce weed pressure in fresh market spinach fields.
- Author: firstname.lastname@example.org
- Author: Larry J Bettiga
CENTRAL COAST WINEGRAPE SEMINAR
WHEN: Thursday, March 16, 2017
WHERE: Monterey County Agricultural Center
1432 Abbott Street, Salinas, CA, 93901
TIME: Registration: 1:00 pm – Meeting: 1:30 – 5:00 pm
Red Blotch Disease – Update on Vector Spread and Consequences of a Field Infection– Rhonda Smith, Viticulture Farm Advisor, University of California Cooperative Extension, Sonoma County.
Virginia Creeper Leafhopper Identification, Biology and IntegratingManagement Practices with Existing Leafhopper Populations -Houston Wilson, Post-doctoral Researcher, Department of Environmental Science, Policy and Management, University of California, Berkeley
Effect of Planting Methods and Root Trimming on Early Vine Development– Larry Bettiga, Viticulture Farm Advisor, University of California Cooperative Extension, Monterey, Santa Cruz and San Benito Counties.
PCA and CCA credits have been requested. For more information or directions call (831) 759-7350. Please call ahead for arrangements for special needs - every effort will be made to accommodate full participation.
- Contributor: Steven T. Koike
- Author: Shimat Villanassery Joseph
Springtail (Protaphorura fimata) (Figure 1) is a serious pest of lettuce in the northern part of Salinas Valley of California. The direct seeded young lettuce seedlings in fields with high densities of springtail show retarded or stunted growth and do not emerge in a synchronous pattern (Figure 2). Springtails are reported to feed on soil fungi, decaying plant materials and live roots.
Springtails attack the germinating seeds of the lettuce, but it is not certain if irregular or inconsistent plant stand is due to the persistent feeding by springtail on both germinating and developing seedling stages of lettuce. Springtail continue to occur in the soil beyond 30 days after planting. Knowing the most vulnerable stage(s) of lettuce to springtail feeding will help in determining the best timing for control measure intervention to achieve a uniform lettuce stand.
Lettuce fields are heavily irrigated at least once before and up to three weeks after planting the seeds for uniform seed germination and seedling establishment. However, the behavioral response of springtail to feeding injury on lettuce under high soil moisture condition has not yet been studied in the central coast of California.
Similarly, the temperature has a profound impact on lettuce plant development as well as the growth and activities of springtail. Springtail has been found causing crop losses during February to May in the Salinas Valley and beyond June, springtail related problems are not widely reported. Perhaps slower lettuce seed germination and subsequent development during cooler seasons (January to May) is the pre-disposing factor as seedlings are exposed to springtails for an extended time frame than during the rest of the year. The relationship between temperature and springtail feeding of germinating lettuce seeds has not been investigated.
A study was conducted to determine the effect of germinating stages of lettuce seeds (up to 7 days after planting), soil temperature and moisture to springtail feeding injury.
Germinating seeds or one day old lettuce seedlings were the most vulnerable stage to springtail feeding, resulting in reduction in seedling growth. Thus, it appears that once the roots are established in the soil, lettuce is less susceptible to springtail feeding injury. Because the germinating phase of the plants is more likely to be injured, springtail monitoring activity should start prior to planting the seeds to determine the presence of springtail in the soil. Previous studies showed that, beet or potato slice baits attract springtail if placed in the top layer of the soil; thus, these baits could be used for monitoring springtail activity in the soil. If the soil is not moist, the baits may not capture springtail and springtail activity may go undetected.
When the experiments were conducted with germination phase in the temperatures as low as 41°F, springtail feeding was still evident. This suggests that although the seed germination and seedling development is progressing slowly in the cooler temperatures, springtail can be still active in feeding if there is sufficient moisture in the soil. Also, this suggests that lettuce seedlings might require prolonged protection from springtail with additional insecticide sprays until the seedlings are established in the cooler temperatures especially in spring and early summer (January to May). In the later part of summer and fall, the temperatures are higher than 60°F even at nights, which allows the seeds to germinate and develop quickly and not providing springtail to persistently feed and cause economic damage. In these circumstances, an at-plant application of insecticide is likely to provide adequate springtail control and multiple applications may not be required.
High moisture content in the soil will favor springtail feeding on the germinating lettuce seeds. In the Salinas Valley, before the lettuce seeds are planted, fields are pre-irrigated to aid land preparation and bed shaping. It has been observed that the springtail density increased from the sub-surface of soil when the field was recently irrigated or after a rain event. This cultural practice which maintains high moisture levels for seed germination on the sub-surface profiles of the soil might be favoring the faster buildup of springtail populations. Springtail captures in bait traps were greater immediately after irrigation.
Clearly, this study demonstrates that early lettuce seed development stages are the most vulnerable to springtail feeding injury. Moisture has a profound effect on springtail feeding on germinating lettuce seeds. This study also suggests that springtail can attack the germinating lettuce seeds at all growing temperatures in the Salinas Valley, although the seed germination and subsequent seedling development at cooler temperatures would increase the vulnerability of lettuce seeds to springtail feeding. This information provides insights not only on the timing of protection but the extent of protection under various temperature ranges also in managing springtail in the Salinas Valley. Plants growing the cooler temperature need prolonged protection for springtail if adequate moisture is present in the top soil of the bed. In the warmer temperatures, seed development would occur rather quickly which suggests that prolonged protection against springtail is not necessary. These results warrant the need for more field studies on protecting lettuce seeds from springtail in the cooler temperatures especially during spring and early summer lettuce plantings in the Salinas Valley.
If interested in the details of the study, please read the published article: