Now that the wheat and oats have been harvested, don’t forget to check these fields for weeds.  Annual weeds that appear after wheat harvest should be clipped as needed to prevent seed production.  Yellow foxtail, common ragweed, crabgrass and barnyardgrass are common annuals in wheat stubble that can quickly go to seed if not mowed or sprayed. 

        Harvested wheat fields with infestations of perennial broadleaf weeds like Canada thistle, hemp dogbane, field bindweed or milkweed can be treated with glyphosate, dicamba, 2,4-D or combinations of these herbicides.  Scout fields to determine the location and approximate acreage that may need treatment.  Wait until the weeds have regrown to 12 inches or more in height before spraying.  As with quackgrass, we can treat perennial broadleaves any time between late August to early October and achieve maximum effectiveness with these systemic herbicides because the weeds are actively translocating sugars and starches into the root system in preparation for winter.  

        Oat fields harvested for grain where alfalfa was underseeded need to be monitored to be sure weeds are not competing too aggressively with the alfalfa.  If crabgrass or other annual grasses predominate, consider applying Poast Plus or Select when grasses are 3 to 6 inches tall.  Annual broadleaves in these situations are best controlled by clipping the field as necessary. 

        Summer seedings of alfalfa done after wheat harvest very often have volunteer wheat as the most serious weed problem.  This is not likely if fields are moldboard plowed before seeding alfalfa, but with disking and in no-till plantings, winter wheat often germinates and competes vigorously with alfalfa.  If the volunteer wheat is serious enough to warrant treatment, apply Poast Plus or Select and the appropriate additives when wheat is 4 to 6 inches tall and actively growing.  Do not wait until next spring to treat as control will be much more difficult.  This treatment will also kill volunteer oats and annual grass weeds, but these will die during the winter and seldom require a herbicide application.