Identifying Delia Root Maggots to Aid Vegetable Seed Growers in the PNW: Final Report

This final report summarizes a BIOAg-funded project examining Delia root maggots as potential pests in Pacific Northwest vegetable seed production. The team planted a controlled spinach seed trial at WSU Northwestern Washington Research and Extension Center, tested several seed treatments, monitored predicted seedcorn maggot timing, and destructively sampled plants for larvae or pupae. Although Delia flies were present in the region based on sticky card captures and previous reports, the project did not find substantial maggot pressure or clear economic damage during the study period. Poor spinach emergence appeared more closely related to seed treatment effects, planting conditions, or other factors than to seedcorn maggot injury. The report concludes that seedcorn maggot should remain on growers’ radar, but current evidence does not support additional experimentation in western Washington unless significant outbreaks occur. Future work would depend on strong grower communication and timely response to reported infestations.