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Management of Alfalfa Trap Crops to Prevent First Generation Lygus Bug (Lygus Hesperus Knight) Damage in California Strawberries


The goals of this project are twofold: 1) demonstrate the utility of managed border alfalfa trap crops to improve the economic and ecological sustainability of California strawberries and 2) broadly extend research results to the strawberry industry, for application by both English and Spanish-speaking stakeholders. <ol> <LI> Use mass mark-capture techniques and field-cage exclusion studies to clearly document early season lygus bug immigration patterns and plant preferences.<LI> Compare densities of, and damage rates from, first generation lygus bugs immigrants in strawberries with and without border trap crops. <LI> Document potential control cost reductions and improved fresh market yields provided by alfalfa trap cropping in strawberries. <LI> Develop broadly transferable trap crop action threshold guidelines for spring lygus bug densities in conventional strawberries. <LI> Provide bilingual outreach activities for technology transfer to the strawberry industry. </ol>The expected outputs of this project include:<ol> <LI> a comprehensive understanding of how, when, and where lygus bugs immigrate into conventional strawberry fields, <LI> a thorough analysis demonstrating the efficacy of alfalfa trap crops in reducing lygus bug abundance and damage in strawberries,<LI> an economic analysis that illustrates the profitability of early season trap cropping, <LI> easily transferable action thresholds for treatment of early season trap crops <LI> a robust outreach program that will increase grower awareness and adoption of sustainable IPM techniques for lygus bug control.</ol> It is anticipated that growers who adopt these techniques will experience fewer pest-caused production losses and increased economic income. In addition, a reduction in insecticide applications (lbs/acre) will be documented, as these protocols offer more precise methods of pest suppression. We anticipate that the results of this project will increase the marketability and yields of strawberries. We expect that an increasing number of growers will become acquainted with alfalfa trap cropping and other sustainable practices by project completion. We expect that a significant number of farmers will transition to trap crop use and IPM strategy for lygus bug over the next 3 to 5 years, resulting in a significant decline in their use of insecticides for lygus control. <P>The proposed project will lead to greater multidisciplinary collaboration among researchers, extension personnel, crop consultants, educators, and industry stakeholders.; resulting in the large scale implementation and wider adoption of reduced risk and sustainable agricultural practices. Further, because this strategy is compatible with organic farming and cropping systems other than strawberries (e.g., cotton, , vegetables, seed production, ornamentals, etc.) with similar key pest problems, we suspect the potential reduction in insecticide use, enhanced environmental quality, and increased profits to extend beyond the strawberry production systems.

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Non-Technical Summary: The California Central Coast region accounts for nearly two-thirds of all strawberries grown in California (CSC 2006). In conventional strawberry fields on the Central Coast, a majority of the synthetic insecticides applied are used to prevent damage to fresh market strawberries caused by lygus bug, (Lygus hesperus Knight). In 2007, approximately 85,000 AI lbs of commonly used lygus insecticides were applied in regional counties (CDPR 2007). Given this situation, new materials and techniques for controlling lygus bugs have been explicitly identified as one of the most critical research needs "to sustain the viability of the California strawberry industry." This study focuses on quantifying the control potential of interfering with the early season movement of Lygus between conventional strawberries, alfalfa trap crops, and weed host plants. Knowledge of Lygus dispersal patterns between valuable cash crops, such as strawberries, and non-crop source-sink relationships (alfalfa and weed hosts) will provide insight into how to manipulate landscape elements in space and time for other western crops. A robust outreach program based on field research results will increase grower awareness and adoption of sustainable, reduced risk IPM techniques for lygus bug control, especially among Spanish-speaking strawberry growers who make up a significant percentage of the Central Coast industry, yet are often not exposed to research-based management alternatives due to language barriers. Our research methodology focuses on an innovative approach to study Lygus dispersal that can be used for implementing landscape level IPM in other western cropping systems (e.g., cotton, stone fruits, vegetables and seed, nurseries, etc.). <P> Approach: Four transects will each cover three sampling zones: edge, mid-field and interior. In each sampling zone, two 100-suction samples will be taken weekly from each transect. Immigrating lygus bug adults will be excluded from portions of field edge and interior alfalfa trap crops; densities will be compared with uncovered alfalfa at the same distances. Alfalfa will be covered in early April of each sample year and covers removed 30 and 60 days later to record lygus abundance relative to uncovered alfalfa. The contents from each vacuum sample will be labeled, placed in a 3.8-liter plastic zip-loc bag, and stored in a freezer. Samples will then be defrosted, sorted, and counted. Mean insect abundance will be compared using an ANOVA model. To determine the preferences of spring-time immigrating lygus adults, a protein mark-capture technique will be utilized. Wild flowering vegetation located 20 ft. from a field edge will be sprayed with both a 33% milk and a 12% chicken egg whites solution. Lygus bug adults will then be collected from four blocks of field-edge trap crops and adjacent strawberry rows closest to the marked vegetation. Individual adults and nymphs will be sorted, separated and sent to the USDA Laboratory in Maricopa, AZ. An aliquot will then be used to assay for the presence of egg white and milk by the enzyme-linked immunosorbent assays (ELISA). Analysis will calculate the percentage of captured lygus bugs that were marked and the area (plant host and field location) in which they were caught. Plant host preference, as determined by the percentage of captured and marked individuals will be determined by a Pearson's Chi-Square Analysis. In order to make an economic comparison between the costs and returns associated with the managed alfalfa trap crop treatment and a grower's standard whole field spraying treatment without trap crops, we will construct a net income budget, incorporating costs of production, yield, and price calculations for the two treatments. Net yield calculations will be made by applying the lygus bug damage observed during this study to expected yield records provided by the grower. To determine the effectiveness of directed insecticide applications for controlling lygus bugs in alfalfa trap crops, eight field edge trap crops will be randomly assigned to one of two treatments: sprayed alfalfa or unsprayed alfalfa (control). Each week from May through July, all eight trap crops will be sampled for lygus bug abundance. Samples will consist of 100 suction samples per trap crop. Lygus bug damage will also be examined in these plots. Both marketable and "cat-faced" strawberries will be recorded weekly to determine percent lygus damage rates. Within each row, 25 plants will be randomly selected for assessment. Percent damage estimates due to treatment will be analyzed using arcsine transformations (to meet assumptions of normality) and ANOVA model. Costs of production will also be estimated per acre by grower cooperators in post harvest interviews.

Swezey, Sean
University of California - Santa Cruz
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