Get an early start on weed control in soybeans
Fall harvest is a good time for producers to assess the weed problems they had in soybean fields this year, and plan a good weed control program for next year. In most cases, it is no longer possible to rely strictly on glyphosate for broadleaf weed control in Roundup Ready soybeans. Before deciding what herbicide program to implement, it is necessary to identify the problem weeds in each field, and what kind of herbicide resistance issues might be present. Some good options for the most common broadleaf weed and grass problems include:
* Pigweeds (including waterhemp and Palmer amaranth). Glyphosate-resistant waterhemp has exploded across eastern Kansas in recent years, and glyphosate-resistant Palmer amaranth is now becoming more common as well. For preemergence pigweed control, the Valor-based herbicides (Valor SX, Valor XLT, Fierce, Gangster, Envive, and Enlite) and Authority-based herbicides (Authority Maxx, Authority XL, Authority First, Sonic, Authority Assist, Authority MTZ, and Spartan) can all provide very good to excellent control to supplement a postemergence program. Prefix is another excellent “foundation” herbicide for residual pigweed control in soybeans and can be applied early postmergence as prior to emergence. Intrro, Dual, Outlook, and Prowl products can also provide some early-season pigweed control, but generally are not as effective as those previously mentioned products. Zidua and Anthem contain the active ingredient pyroxasulfone (also a component of Fierce). Pyroxasulfone has a similar mode of action to Intrro, Dual, and Outlook but may provide longer residual control of pigweeds.
Although some of these herbicides can be applied in the fall or early spring, those treatments generally will not persist long enough to give good pigweed control into the soybean growing season. So if pigweed is the primary target, treatments will be most effective if applied no more than two weeks prior to planting. If glyphosate-resistant pigweeds escape preemergence control, the primary postemergence tank-mix options would be Cobra, Flexstar, or Ultra Blazer. However, timing is critical for good control. These products should be applied before pigweeds exceed 4 inches tall for optimum control.
* Velvetleaf. Glyphosate is not always entirely effective on velvetleaf. To assist in velvetleaf control, the Valor-based and FirstRate-based herbicides (Valor SX, Valor XLT, Fierce, Gangster, Authority First, and Sonic) are some of the most effective preplant and preemergence herbicides you can use. Postemergence tank-mixes to enhance velvetleaf control would include FirstRate, Cadet, and Resource.