Evaluating wheat trap cropping and Spinosad bait to manage wireworms in lettuce production

Wireworms (Agriotes spp. and Limonius spp.) are major pests of vegetable production in western Washington. The introduced European species of A. lineatus and A. obscurus have been found throughout western Washington contributing to increased reports of damage in recent years. Organic producers have very few options for control of wireworms and severe infestations can result in devastating crop loss. Using transplanted lettuce (Lactuca sativa cv ‘Muir’) as a model crop we investigated the impact of trap cropping with wheat (Triticum aestivum), and applying a spinosad insecticidal bait, on crop survival and wireworm distribution in the soil. Total wireworm response varied significantly by treatment (p < 0.001) with the greatest wireworm abundance in the soil where wheat was planted. Lettuce yield did not differ among treatments (p > 0.05). However, percent total lettuce lost varied significantly among treatment combinations (p < 0.001). Post-hoc analysis suggests that while spinosad and control treatments showed no difference, wheat trap cropping can significantly reduce lettuce loss. Based on our findings, trap cropping with wheat has potential to be integrated with other management strategies on organic vegetable farms to reduce crop loss.