PRE-emergence herbicides are the foundation for good weed control in corn and soybeans, particularly with the spread of herbicide-resistant weeds. The use of some PRE-emergence herbicides is limited to certain regions or counties in Wisconsin. Prior to selecting a herbicide for your weed management program, make sure the same is approved for use in your region by the Department of Agriculture, Trade and Consumer Protection (DATCP). Below are examples of herbicides that have geographic restrictions in Wisconsin.
Atrazine (Photosystem II Inhibitor, Group 5) is a commonly used corn herbicide. In Wisconsin, there are areas where the use of atrazine is prohibited (see map below). For more information on atrazine restrictions check DATCP information on Atrazine and always read the product label for rates and restrictions.
Isoxaflutole (HPPD-inhibitor, Group 27) is a PRE-emergence herbicide used for weed control in corn. Isoxaflutole-based herbicides such as Corvus and Balance Flexx are approved for use in 12 Wisconsin counties (Columbia, Dane, Fond du Lac, Jefferson, Sauk, Grant, Lafayette, Walworth, Dodge, Green, Rock, and Waukesha; see map below). See product label for rates and restrictions.
Chlorimuron-ethyl (ALS-inhibitor, Group 2) is the active ingredient in the POST-emergence soybean herbicide Classic. Chlorimuron-ethyl is also an active ingredient in several PRE-emergence soybean herbicides such as Authority XL, Canopy, Canopy EX, Enlite, Fierce XLT, Rowel FX, Synchrony XP, Trivence and Valor XLT. The use of most chlorimuron-ethyl based herbicides is typically limited to fields south of I-90 between Lacrosse and Madison and fields south of I-94 between Madison and Milwaukee (see map below). See product label(s) for rates and restrictions.
Fomesafen (PPO-inhibitor, Group 14) is the active ingredient in the POST-emergence soybean herbicide Flextar. Fomesafen is also an active ingredient in the PRE-emergence soybean herbicides Prefix and Warrant Ultra. The maximum use rates of fomesafen changes across Wisconsin (e.g., a higher rate can be used south of U.S. Highway 18 between Prairie Du Chien and Madison, and south of Interstate 94 between Madison and Milwaukee [Region 3 in the map below]). In Region 3, a maximum of 0.313 lb ai/A of fomesafen may be applied in alternate years. In Region 4, a maximum of 0.25 lb ai/A of fomesafen may be applied in alternate years. Due to carryover potential, don’t apply fomesafen on the white regions in the Wisconsin map. See product label(s) for rates and restrictions.
Pendimethalin (Microtubule Inhibitor, Group 3) is the active ingredient in the PRE-emergence herbicide Prowl H20. There are no geographic restrictions for Prowl H2O use in Wisconsin; however, there are differences in the application window for corn and soybeans. In corn, Prowl H2O can be used PRE-emergence and POST-emergence [“until field corn is 30-inches tall (20-inches to 24-inches tall for popcorn, popcorn seed, field seed, and fresh sweet corn) or in the V8 growth stage, which ever is more restrictive” according to the label]. In soybeans, Prowl H2O can only be sprayed PRE-plant in Wisconsin. See label for rates and restrictions.