Organically acceptable seed corn maggot control on Pacific Northwest vegetable crops

Seed corn maggot (Delia platura) infestations reduce germination and stand establishment of Pacific Northwest vegetables. Crops impacted include carrots, onions, beans, and corn. These crops are traditionally treated post-planting with with broad-spectrum insecticides. For the last several years seed treatments of cloronicotinyl insecticides have provided effective control of maggots, but to date there were no effective treatments available for maggot control for organic producers. In 2007 plantings of onions and carrots were established near Alderdale, Washington, USA. The onion seeds were pelleted by 11 seed treatment vendors with the insecticide spinosad and raw carrot seed was treated with a topical application of spinosad. Stand establishment of carrots and onions treated with spinosad was significantly greater (p<0.05) then stand establishment in plots planted with untreated seed. Additionally, spinosad seed treatment was equivalent to conventional seed treatments and post-planting insecticide treatments for stand establishment.

In 2008, experiments were conducted to test the efficacy of spinosad as a seed treatment for maggot control in peas, dry beans, carrots, onions, and sweet corn in the Columbia Basin. For each crop, rates were calculated based on seed size and the amount of product that could be applied per acre. Seeds were planted in commercial fields in a randomized complete block design with four replications. All the plots established with spinosad treated seeds resulted in significant increase (p<0.05) in stand establishment. When labeled for use as a seed treatment spinosad in the Entrust™ formulation will provide organic producers with a solution for mitigating stand loss caused by seedcorn maggot in vegetable crops in the Pacific Northwest.