Adaptation and evaluation of the WEEDSIM weed management model for Michigan

The WEEDSIM bioeconomic model was developed in Minnesota and was designed t o support weed management decisions for both soil-applied and postemergence weed control programs in Zea mays and Glycine max. In this research, we ad apted the WEEDSIM weed management model to Michigan by modifying the crop y ield loss functions and herbicide efficacy ratings. We then validated the c omponents of the model and determined whether WEEDSIM led to more profitabl e weed management than recommendations from SOYHERB or CORNHERB, computer d ecision aids based solely on herbicide efficacy and cost. The crop year sig nificantly influenced the weed-free yield in Z, mays and G. max, but the we ed-crop interference function did not change each year. Total weed seed inc reased in the untreated compared with the weed-free control over the 3-yr p eriod. Weed seed did not increase significantly in WEEDSIM preemergence/pos temergence (PRE/POST), WEEDSIM postemergence, or CORNHERB or SOYHERB treatm ents compared with the weed-free control, although annual grass seedling de nsity at the time of postemergence herbicide application had increased by 1 995 in the WEEDSIM postemergence treatment in G. mau because of a 2,4-D ami ne application only in Z, mays in 1994. WEEDSIM PRE/POST and CORNHERB provi ded excellent weed control in all three years, and WEEDSIM PRE/POST resulte d in gross margins over weed control costs equal to or greater than CORNHER B recommendations. In G. max, Chenopodium album and annual grass control wa s excellent in all three years for WEEDSIM PRE/POST, WEEDSIM postemergence, and SOYHERB treatments. The highest average gross margin for the 3-yr stud y was from mechanical weed control in 76-cm-wide rows of G. max ($806 ha(-1 )) and from SOYHERB in 38- and 19-cm-wide rows of G. max ($776 and $808 ha( -1), respectively). WEEDSIM recommendations controlled weeds and maintained crop yield in both Z. mays and G. max.