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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #440190

Research Project: Monitoring and Cultural Strategies to Reduce the Impact of Thrips-Transmitted INSV Affecting Lettuce on the Central Coast of CA

Location: Crop Improvement and Protection Research

Project Number: 2038-22000-020-012-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Apr 1, 2021
End Date: Sep 30, 2024

Western flower thrips is the primary insect vector for impatiens necrotic spot virus (INSV), a virus that had devastating effects on lettuce production in the Salinas Valley in 2019 and 2020. Only limited strategies exist for thrips management due to the lack of efficacious chemistries and there are no direct methods for managing INSV. This proposal has three objectives that will focus on, 1) continuing the Salinas Valley thrips monitoring program and reporting of populations throughout the 2021 lettuce season to build historical data, 2) continuing surveys to identify key non-lettuce hosts for INSV on the Central Coast, and 3) explore the use of early season roguing strategies (i.e. removing INSV-infected lettuce plants) as a means for reducing the spread of INSV in lettuce fields. These studies contribute to our greater understanding of the epidemiology of thrips and INSV and will provide useful information for developing weed abatement programs and in-field strategies as part of an IPM program for thrips and INSV in lettuce production on the Central Coast of California.

Objective 1: Double-sided yellow sticky cards in 21 locations in the Salinas Valley will be collected and replaced weekly. Each card will be counted for thrips and documented. Graphs will be sent to the University of California Cooperative Extension (UCCE) of Monterey County and presented on the University of California Division of Agriculture and Natural Resources (UCANR) Salinas Valley Agriculture blog to provide updates to the industry. Objective 2: Three sampling surveys will be conducted in Spring 2021, Summer 2021, and Fall/Winter 2021 and take place in four locations in the Salinas Valley, as performed previously. The North, West, and East locations are regions that experienced high levels of INSV in 2019 and 2020, while the South location reported relatively low levels of INSV incidence. Sampling will focus on the top 10 hosts for INSV that were previously described but will also include hosts that have not been extensively sampled. Each sampling period will include 150-300 samples collected from each location, with each sample consisting of tissue collected from an individual plant. A minimum of 10 samples per species will be collected at each location, when possible. Plant species will be identified and processed for detection of INSV using TAS-ELISA at USDA. Species that are determined to be a host for INSV using TAS-ELISA will also be validated by either Immunostrip and/or RT-PCR. Objective 3: Spring lettuce fields will be identified based on reports of INSV infections from growers and PCAs. Each field will be scouted to assess the disease pressure. If suitable, four blocks at 33 x 30 ft. (consisting of ~750 lettuce plants) will be flagged off, with each block exhibiting the same levels of INSV infection. Two blocks will receive the rogue treatment (i.e. INSV symptomatic plants will be removed from the field), while the remaining two blocks will not be rogued (untreated). Blocks will be evaluated for INSV symptoms every 7-10 days and any new plants showing INSV symptoms will be removed from the blocks receiving the rogue treatment. Prior to harvest, a final evaluation will be performed to determine the impact of roguing on INSV incidence. Trials will be conducted in a minimum of three fields during the Spring lettuce season (March – May) three fields during the Summer lettuce season (June – August) and three fields during the Fall lettuce season (September – November).