MULTIYEAR VALIDATION OF A DECISION AID FOR INTEGRATED WEED MANAGEMENTIN ROW CROPS

WEEDSIM is a bioeconomic decision aid for management of annual weeds i n corn and soybean. It was field-tested for 4 yr in Minnesota. The dec ision aid has two categories of management recommendations: soil-appli ed plus postemergence (PRE+), based on estimated weed seedbank composi tion and density; and postemergence (POST), based upon observed weed s eedling composition and density. Weed densities, weed control, herbici de use, environmental impact of herbicide use, weed management costs, crop yields, and economic returns that resulted from PRE+ and POST rec ommendations were compared to those associated with herbicide manageme nt systems (HERB) that were standard for the region. After 4 yr of app lying WEEDSIM recommendations to the same plots, there were no increas es in annual weed densities (seedbanks, seedlings, established plants, or seed production) or decreases in weed control or crop (soybean, ro tation corn, and continuous corn) yields, compared to HERB. WEEDSIM re commendations resulted in average annual herbicide applications of 1.1 kg ai ha(-1) for PRE+ and 1.0 kg ai ha(-1) for POST, compared to 3.5 kg ai ha(-1) for HERB. Environmental impact indices associated with PR E+, POST, and HERB were 0.75, 0.71, and 0.54, with the lowest value in dicating greater environmental risk than the two higher values. Simila rly, average weed management costs were $24, $33, and $77 ha(-1) for P RE+, POST, and HERB, respectively. Based on crop prices of $94 Mg-1 fo r corn and $220 Mg-1 for soybean, the average gross margins over weed control costs were higher for PRE+ ($509 ha(-1)) and POST ($522 ha(-1) ) than for HERB ($455 ha(-1)). In general, WEEDSIM appeared to make ma nagement recommendations that adequately controlled weeds, maintained crop yields, reduced herbicide use, decreased environmental risk, lowe red weed management costs, and increased gross margins over weed contr ol costs compared to the use of herbicides standard for the region.