Implementing Sustainable Management Plans for the Clover Seed Weevil in White Clover Seed Production

Commodities

Practices

White clover seed production in Oregon is increasingly constrained by the clover seed weevil (CSW; Tychius picirostris), a key pest that can cause substantial reductions in seed yield. Current management practices rely largely on calendar-based insecticide applications and crop growth stage indicators rather than pest phenology. As a result, insecticides are often applied without being properly timed relative to vulnerable life stages. Unnecessary applications increase selection pressure on CSW populations, accelerating the development of insecticide resistance. In recent years, reduced efficacy of commonly used insecticides has been reported, highlighting an urgent need for improved management strategies that incorporate better timing, monitoring, and resistance stewardship.

This project will develop a biologically based phenology model that links CSW life stages to cumulative degree-days. Field monitoring will be conducted at commercial sites to document seasonal patterns of adult activity and larval damage. Weather data will be integrated with field observations to identify degree-day thresholds associated with key life stages and optimal management windows. Model predictions will be validated across locations and years and compared with traditional calendar-based timing. Further, biochemical assays with field-collected CSW populations will be conducted to characterize detoxification enzymes underlying resistance to broad-spectrum insecticides. These findings will guide future research on effective and pollinator-friendly chemistries.

Outreach will include on-farm monitoring, demonstration trials, grower meetings, and in-season pest alerts. A CSW Phenology Decision Calendar, one refereed manuscript, and multiple extension education materials (newsletter articles, slide decks, and factsheets) will be developed and disseminated through OSU Extension, industry meetings, and digital platforms.

Research Objectives

1. Build and validate phenology models predicting CSW adult emergence and larval development to refine treatment windows in Oregon production conditions. Findings will be integrated into an interactive decision-support platform to facilitate real-time recommendations for growers and crop consultants.
2. Characterize detoxification enzyme profiles (e.g., cytochrome P450s, esterases, and glutathione S-transferases) in field-collected CSW populations relative to a known susceptible population. Identify the biochemical basis of insecticide resistance mechanisms to guide future product registrations, label recommendations, and stewardship practices for white clover seed crops. Findings will be shared with the Oregon Clover Commission, Oregon Department of Agriculture, the IR-4 Project team, and other regulatory partners.

Educational Objectives

1. Increase producer and agricultural professional knowledge of CSW phenology and insecticide resistance management (IRM), as measured by pre- and post-program evaluations at field days, workshops, and meetings. This objective will ensure rapid dissemination of project findings, strengthen grower understanding of IRM principles, and enhance the long-term resilience of Oregon's clover seed industry.
2. Support the adoption of phenology-based management practices by delivering decision tools and Extension programming to document changes in timing decisions and the reduction of unnecessary insecticide applications.