- Author: Richard Smith
1st Announcement- Save the Date
2015 Salinas Valley Weed School
Thursday, November 12
8:00 a.m. to 12:00 noon
Agricultural Center Conference Room
(1432 Abbott Street, Salinas)
This meeting will cover a number of new techniques for controlling weeds in vegetable crops. In addition the effect of weeds on bagrada bug populations and new mechanical tools will be discussed.
4.0 Continuing education credits have been applied for. Please call ahead for special accommodations.
For more information call Richard Smith (831) 759-7357
See attached file for full agenda./h2>/h2>/h2>/h2>/h1>/h1>
- Author: Shimat Villanassery Joseph
Cabbage maggot (Delia radicum) is a serious insect pest of Brassica crops such as broccoli and cauliflower in the Central Coast of California. These crops are grown throughout the year; as a result cabbage maggot problems persist year long.Cabbage maggot eggs are primarily laid in the soil around the crown area of the plant. A single female fly can lay 300 eggs under laboratory conditions. The eggs hatch within 2-3 days and the maggots feed on the taproot for up to three weeks and can destroy the root system of the plant. The maggots pupate in the soil surrounding the root system and emerge into flies within 2-4 weeks. Severe cabbage maggot feeding injury to the roots cause yellowing, stunting even plant death.
Control of cabbage maggot on Brassica crops primarily involves the use of soil applied organophosphate insecticides such as chlorpyrifos and diazinon. However, the persistent use of organophosphate insecticides has resulted in high concentrations of the insecticide residues in the water bodies posing risks to non-target organisms and public health through contaminated water. Currently, use of organophosphate insecticides is strictly regulated by California Department of Pesticide Regulation. There is therefore an urgent need to determine the efficacy of alternate insecticides for cabbage maggot control.
The efficacy of 29 insecticides was determined against cabbage maggot through a laboratory bioassay by exposing field collected maggots to insecticide treated soil immediately after application. Three parameters were used to evaluate efficacy (1) proportion of maggots on the soil surface after 24 h, (2) proportion of change in weight of turnip bait, and (3) dead maggots after 72 h. Based on the assays, 11 insecticides performed better and they were Mustang, Torac, Danitol, Belay, Capture, Warrior II, Lorsban, Mocap, Durivo, Pyganic and Vydate in the order of highest to lowest efficacy. Eight insecticides were selected based on superior efficacy to determine the length of residual activity on cabbage maggot larvae. The persistence of insecticide activity was greater with Capture, Torac and Belay than with other insecticides tested.
The mode of exposure of insecticides in this study was entirely by contact (through skin) and other modes of exposure such as ingestion (through mouth) or through respiratory holes (spiracles) were not investigated. Some of the insecticides tested in the study were insect growth regulators (IGRs) (Dimilin, Rimon, Trigard, and Aza-direct), which normally interfere with the growth and development of the insect and they showed a low efficacy against cabbage maggot larvae. Entrust (spinosad) showed a moderate efficacy possibly because the primary mode of exposure to Entrust is by ingestion. The diamide insecticides (Beleaf, Coragen and Verimark) have systemic activity as they move within the plant and likely away from the site of application. It is possible that the soil applied diamide insecticides are absorbed by the roots and translocated to the above ground plant parts with little effect on the feeding larvae in the tap roots.
This study was conducted under controlled conditions in the laboratory and the results may not be entirely consistent in field conditions. The Brassica fields in the California's Central Coast are profusely sprinkler irrigated up to three weeks after sowing to ensure uniform germination and proper establishment of plants. It is likely that applied insecticides are partially or completely leached out of the root zone area without providing anticipated maggot control. In this study, insecticides were drenched into the cup and none of the applied insecticide solution leached out. Therefore, it is likely that the insecticides were more effective in the laboratory assay than they would be in the field. Certain insecticides such as pyrethroids tend to bind to the soil organic matter. The organic matter in the California's Central Coast soils can be up to 4%, which could reduce the availability of soil applied pyrethroid insecticide to the root zone where cabbage maggot larvae typically colonize. In situations with poor insecticide spray coverage, invading cabbage maggot larvae are possibly exposed to no or sub-lethal doses of the soil applied insecticide and may be able to penetrate the soil and infest the roots. The air temperature in the field at the time of insecticide application may influence the efficacy of the applied insecticide. The efficacy of pyganic decreased as the temperature increased against onion maggot. This suggests that application of pyrethroid insecticides should be avoided during warmer periods of day.
Other field conditions that influence efficacy of insecticides are cabbage maggot incidence and frequency of invading cabbage maggot flies on Brassica crop in the Central Coast of California. The earliest peak of cabbage maggot infestation occur a month after sowing broccoli seeds and infestations can be continuous until harvest. Also, insecticides applied at sowing as a banded spray on the seed lines did not provide adequate cabbage maggot control based on the insecticide efficacy trials conducted in commercial broccoli fields. These findings suggest that delaying the insecticide application by 2-3 weeks after sowing is more likely to maximize maggot control. Because the cabbage maggot infestation can last several weeks, insecticides with extended persistence of efficacy would increase the value for cabbage maggot control. Overall, results show that Capture, Torac and Belay which performed effectively against cabbage maggot for a month after application. This indicates that insecticides used before the first peak of infestation may protect the younger stages of the Brassica plants allowing them to establish and tolerate milder cabbage maggot infestations thereafter.
In conclusion, 11 insecticides with high efficacy were identified for future investigation. Future studies will focus on determining the effects of application timing and delivery methods compatible with cabbage maggot incidence in both directly sown and transplanted Brassica crops in the Central Coast of California.
If you are interested in reading the details of this study, please click the link below to access the published article.
Authors: Richard Smith1, Michael Cahn1, Tamara Voss2, Toby O'Geen3, Eric Brennan4, Karen Lowell5 and Mark Bolda6
1 – UC Cooperative Extension, Monterey County; 2 – Monterey County Water Resources Agency; 3 – Dept of Land Air and Water Resources, UC Davis; 4 – USDA Agricultural Research Service; 5 –USDA Natural Resources Conservation Service; 6 – UC Cooperative Extension, Santa Cruz County.
For access to full report please visit http://cemonterey.ucanr.edu/files/219694.pdf
Rainfall that cannot be infiltrated within a field will run-off to surrounding areas and eventually flow off-site. Several strategies can capture, slow, and facilitate infiltration of such run-off. In general, strategies become more costly and harder to implement the further downslope they occur. Row arrangement that slows run-off is more cost effective than building large recharge basins that routinely fill with sediment. Full control of run-off almost always requires suites of practices rather than a single approach. Many of the strategies described below are described in more detail in the Resource Conservation of Monterey County and Monterey County Agricultural Commissioner's 2014 publication, Hillslope Farming Runoff Management Practices Guide. This 52 page guide is available as a free download here: http://tinyurl.com/Runoff-Management-Practices.
Permanent Vegetative Cover. In areas of the ranch that routinely receive runoff, establishing permanent vegetative cover is very helpful. While this removes ground from production, if it is a part of a ranch that is routinely damaged by winter rains it may allow management strategies that are worth the sacrificed ground. For example, a grassy area that receives relatively sediment free runoff could serve to defuse energy and infiltrate water and avoid need for regular sediment basin maintenance. Where such an area overlies a soil that allows deep percolation this will lead to groundwater recharge. If permanent cover is not practical or acceptable from an operational perspective, setting aside an area for this purpose that can be planted later in the spring (to allow for more dense vegetation to be disked in) may still be beneficial. Grassed waterways may serve this function, and are typically planted to perennial grasses. Some ranches with wash facilities on site may have areas that receive waste water. Where practical, if water can be carried to this area during rainy winter months when production (and wash activities) are not underway extra benefit of the area may be possible. Vegetated filter strips placed strategically along the contour of a slope may be feasible in some operations, or narrower areas strategically placed to diffuse the energy of water sheeting off a plastic hoop house. For example, seeding this splash impact area to a low grass may keep the soil surface more open and able to infiltrate water than one with poor soil structure resulting from drainage onto bare ground.
Sediment traps: Because significant erosion can occur during major storm events, structures are needed that can minimize clogging of downstream run-off control practices such as vegetated ditches, weirs, and retention basins. Sediment traps can intercept and settle sand and large silt particles suspended in run-off from fields during storm events. These structures are usually shallow basins (2 to 3 feet deep) located at the lower corner of a field. They intercept run-off before it flows into major ditches that convey it across a ranch. Trapped sediment needs to be removed after major storm events for these structures to function efficiently during the winter. A check at the outlet of the trap can be used to adjust the height of water by adding and removing slats of wood. Changing the height of the check dam allows more time to allow for sediment in a heavy flow with resultant high water level, to settle out before overflowing into a culvert or other conveyance.
Enhance ditches for infiltrating run-off: Permanent ditches that convey field run-off can be enhanced to minimize bank erosion during storm events and increase infiltration. Many farm ditches are narrow with steep banks that are prone to erosion and blow-outs during large storm events. Wider ditches with a U-shape instead of a V-shape reduce erosion by spreading the water and reducing the erosive energy as it flows. Water in a wider ditch may also flow more slowly, allowing more opportunity for infiltration and recharge to groundwater. Providing some armor to soil (e.g. rocks) to dissipate the energy of run-off entering from culverts and smaller tributaries can also protect against erosion, although it is important to place such protection carefully to avoid creating paths of preferential flow that may be even more damaging. Weirs can be spaced at regular distances within the ditch to slow the flow of water during moderate run-off events. These weirs can be designed to be removable or so that the cross section of the passage way can be adjusted to handle high flow rates without overflowing the banks of the ditch. During small and medium storm events, weirs can retain and infiltrate a large portion of the run-off.
Vegetating ditches Vegetation in permanent ditches helps protect the banks to prevent erosion, and avoid blow outs with massive volumes of sediment during large, intense storms. Because infiltration is better when there is good surface soil structure, typically the case when there is vegetation, vegetated ditches may also improve infiltration. Key design features will influence the ability of a ditch to retain its function during large storms. For example, as noted above U-shaped ditches are better than V-shaped ditches. A 1:3 to 1:4 slope (1 foot of depth to 4 feet of width) would be a good target to optimize ditch stability and enhance infiltration. Ditches can be seeded with fast growing grasses such as barley or rye if the objective is to have vegetation only during the winter months. Grasses planted in ditches may be killed with an herbicide before they produce seed, to reduce the potential to attract rodents. Also the ditches can be returned to an unvegetated condition before spring crops are planted. Red fescue provides a dense permanent vegetation that has very small seeds that are less attractive to rodents (Figure 7). Studies conducted at the USDA-ARS research station in Salinas demonstrated that these ditches were effective in infiltrating run-off and mitigating transported sediment and pesticides.
Figure 7. Permanent ditch planted with red fescue can infiltrate run-off and protect the sides of the ditch from eroding during large storm events. This ditch is located at the USDA-ARS along Spence Road in Salinas.
Lined Waterway. If vegetation is not sufficient cover for a conveyance channel use of concrete or rock riprap may be necessary. Some growers use plastic. While this reduces recharge potential as the water does not infiltrate from a plastic lined ditch, if it can safely convey the runoff to a suitable basin where infiltration is possible. The reduced sediment load resulting from the lined ditch will be beneficial. Significant recharge depends on placing the basin on a suitable soil and delivery of relatively sediment free water to ensure that the bottom of the basin retains high infiltration rates.
Retention basins: A basin that can retain run-off reaching the lower end of a ranch can provide an additional opportunity to infiltrate storm water (Figure 8). Retention basins designed for infiltrating run-off can be relatively shallow (2 to 4 feet deep), and can be located in areas of the ranch that are undesirable for farming, such as on an irregularly shaped section of a field. For optimum benefit, it is important to consider soil properties underlying the basin. For example, a soil with a hardpan at 3 feet depth will be less effective than one with no impeding layer. A ditch conveying run-off might be widened to create some of the function of a shallow retention basin, or a berm constructed between a field and roadway can create a retention basin. To avoid blow outs, basins must be sized appropriately, based on expected intensity of storm events and size and slope of the area that will drain to them. The outflow structure of the basin should be engineered to allow controlled overflowing during large storm events and to ensure that outflow is channeled to minimize erosion of the basin and any conveyances that receive overflow. Even dead vegetation on the bottom or sides of a ditch can enhance recharge by creating an organic matter layer that protects surface soil structure and facilitates infiltration.
Figure 8. Shallow retention basins can infiltrate run-off from agricultural fields before it flows offsite
Road Protection. Many of the strategies described above will work on roads as well. A few others may also be useful. For example, use of cross ripping or waterbars on roads that do not need to be driven during winter months may be helpful as supplemental protection when roads are seeded for erosion control. A temporary slope drain may also be used when cost, labor or time constraints make construction of underground outlets and permanent sediment basins impractical. These temporary systems use a flexible pipe to capture concentrated runoff at the top of the slope and convey it downslope to a stable outlet where it is released in a sediment basin or similar.
Citations and Other Resources:
Brown and Caldwell, State of the Salinas River Groundwater Basin, prepared for Monterey County Resource Management Agency, January 16, 2015.
Montgomery Watson, Salinas Valley Historical Benefits Analysis, prepared for Monterey County Water Resources Agency, April 1998.
Soil suitability index identifies potential areas for groundwater banking on agricultural lands. O'Geen, T. et al. 2015. California Agriculture. Online:http://californiaagriculture.ucanr.edu/landingpage.cfm?article=ca.v069n02p75&fulltext=yes
Low residue winter cover crops for winter vegetable production. Smith, R., M. Cahn, A. Heinrich and B. Farrara. YouTube video: https://www.youtube.com/watch?v=k0oVVJ_BA7s
Hillslope Farming Runoff Management Practices Guide. This 52 page guide is available as a free download here: http://tinyurl.com/Runoff-Management-Practices.
Local USDA Natural Resource Conservation Service and Resource Conservation Districts have resources to help growers with farm edge practices: Salinas NRCS office: 831-424-1036 x101, Resource Conservation District of Monterey County: 831-424-1036 x124 0r 126.
- Author: Shimat Villanassery Joseph
Among several species of thrips that invade vegetable crops, western flower thrips [Frankliniella occidentalis (Fig. 1)] is the most destructive species of thrips in the Salinas Valley. They can cause severe feeding injury to all stages of plant development. Early feeding can cause severe stunting or reduce plant development whereas; late feeding can cause visible feeding patches - affecting marketable yield in both the instances. Severe feeding injury is usually associated with very high populations of thrips on the crop. It is likely that recent early surge in thrips populations in the Salinas Valley is related to warmer (high day temperatures) and dry winter.
Thrips is a tiny insect (less than 3 millimeters) and prefers to stay and feed within tight protected areas of the plant such as, between veins or near mid-rib or within the layers or stacks of lettuce leaves or celery stems. Thus, thrips injury was detected in those tight areas of the plant. It is likely that colonizing at those tight areas provide protection from insecticide sprays.
Thrips has a “piercing-sucking” or “punch and suck” mouthpart. Mouthpart of thrips is referred as mouthcone (Fig. 2). Thrips typically feeds using two structures of its mouthcone: (1) a mandible and (2) stylets. As illustrated in the Figure 2, thrips uses the mandible to pierce or punch the plant cell wall and stylets (or needles), which often form a single tube, sucks the liquid food from the plant cell. This feeding apparatus allows thrips to feed on liquid food on a surface or within a plant cell.
As indicated, thrips can cause significant crop loss once its population increases to very high levels. Thrips injury on lettuce may appear as brown streaks, or scarring on the leaves (Fig. 3). If examined closely using magnifying glass, it appears like punctured plant cells and the content removed (Figs. 4 and 5). On celery, the thrips feeding injury is similar but the injured cells appear as raised ridges (Fig. 6). When attacked at the younger stages of the plant development, for e.g., on the growing tips of the cotyledons (Fig. 7), the feeding could deform the true leaves that develop later (Fig. 8).
In addition to feeding injury, western flower thrips are able of transmiting plants viruses (tospoviruses) such as Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV). In the family: Thripidae, there are 1710 species of thrips but only 14 thrips species are currently reported to transmit tospoviruses. Both larval and adult stages of thrips vectors actively feed on the host plants but only early larval instars can acquire tospoviruses and later instar larvae and adults can transmit tospoviruses after a latent period. Adult thrips can acquire tospoviruses, but they do not transmit them because virus could not multiply to sufficient numbers. Also, tospoviruses are not transmitted when the thrips lay eggs into the plant. Thus, each new generation of thrips vectors must acquire the virus as larvae. The weed plants outside the field can be the reservoir for tospoviruses and when the larvae feed on them, they acquire the virus. In the field, larvae feeding on the tospoviruses-infected lettuce plants may also aid virus acquisition. The thrips carrying the virus just need to feed for 10-15 minutes to transmit the virus to uninfected plants.
Typically, bean-shaped eggs are inserted by female western flower thrips into the leaf. Within 5 days, eggs hatch to first instars. If the temperature stays at 86ºF, first instars molt into second instars. This can happen in couple of days in the Salinas Valley. Second instars develop into prepupae within 4-5 days. Most of the prepupae drop to the soil and emerge into adults within 3 days at 86ºF. Pupal stage is the only non-destructive stage of the thrips. Clearly, thrips development is associated to temperature. Adult females lay about 50 eggs and can live up to 4-5 weeks at 86ºF. So, in Salinas Valley due to milder temperature range, western flower thrips may live longer than 5 weeks. Western flower thrips requires a minimum 194 degree days (DD) (min. temp. 49.5oF) to complete a generation, but has been estimated to be as high as 254 DD with a minimum temperature of 43.7oF. Western flower thrips can lay eggs with and without mating. The mated female thrips (fertilized) tend to produce more female offsprings than males whereas, unmated female thrips tend to produce more male offsprings than females.
Thrips are weak flyers but they have fringed wings which help them to get airborne and glide short and long distances. Thrips can stay airborne for about 24 hours in the cooler conditions and can remain without feeding and drinking. They get quickly desiccated if they stay longer in the air. The dispersal of thrips is largely depending on temperature, light, and wind.
To prevent direct feeding injury and viral transmission, it is important that we manage thrips on the crops using the tools such as targeted insecticide sprays. Recent insecticide efficacy studies against western flower thripssuggested that insecticides such as Radiant, Entrust, Lannate, Exirel and Beleaf have decent activity against western flower thrips. Other products, Gladiator and Torac are effective but are not registered for use. Please read the Monterey County crop note (May edition) for details on insecticide efficacy trials. It is important that the growers restrain from repeated use of insecticides within same IRAC class (http://www.irac-online.org/documents/moa-classification/?ext=pdf) in a given season instead rotate insecticides with distinctly different modes of action to reduce development of resistance.
- Author: Shimat Villanassery Joseph