Clover seed weevil management in white clover seed production systems

View the project report

Commodities

• Agronomic: clovers

Practices

• Education and Training: decision support system, extension, on-farm/ranch research
• Pest Management: chemical control, field monitoring/scouting, integrated pest management

Clover seed weevil (CSW), Tychius picirostris Fabricius (Coleoptera: Curculionidae), is a key insect pest in white clover seed production in Oregon. Historically, clover seed growers have relied heavily on broad-spectrum pyrethroid insecticides for CSW management. Since 2017, growers and crop consultants have observed poor efficacy with pyrethroid insecticides, causing serious concern for the white clover seed industry. Moreover, reduced effectiveness of pyrethroid insecticide treatments in a 2021 Oregon State University (OSU) field trial warrants further CSW pyrethroid resistance status evaluation. Available insecticides are limited, leaving few options for growers to rotate between different modes of action (MoA). We aim to i) determine the resistance status to pyrethroids and other MoA using laboratory bioassays, ii) evaluate new MoA and different insecticide timing under field conditions, and iii) develop a scouting method and treatment decision-making guidelines based on the larvae density per seed head. Our education efforts will focus on i) enhancing grower knowledge of CSW biology and optimizing control timing; ii) facilitating training and workshops for calibrating pesticide application equipment and scouting techniques specific to CSW, and iii) gathering input on growers' perceptions of alternative methods of the integrated management plan (IPM). Data from this research will be disseminated during OSU Extension events throughout the project duration. The expected outcomes will include one factsheet, one extension publication, and at least one peer-reviewed journal article. The sustainability goal will be achieved by 1) reducing unnecessary chemical applications and 2) increasing economic return by lowering inputs and improving seed yield.

Our research objectives include:

1. Identify the level of pyrethroid resistance development and toxicology of other insecticide modes of action using laboratory bioassays.
2. Conduct field efficacy tests using new modes of action and different insecticide timings specifically targeted to control clover seed weevil (CSW) larvae.
3. Develop a grower-friendly scouting method and treatment decision-making guidelines based on CSW larvae density per seed head.

The educational objectives of this project will focus on 1) improving current knowledge of clover seed growers and crop advisors on CSW biology and behavior to better time insecticide applications, 2) facilitating the incorporation of insecticide resistance management strategies in clover seed production systems through training and workshops, and 3) gather input from growers and local crop advisors about their perceptions of alternative methods included in the integrated management plan (e.g., host plant resistance, cultural control, and biocontrol).