Winter annual weeds including henbit and common chickweed have become more common while controlling marestail in soybean fields has become increasingly difficult. Fall herbicide applications have proved effective in controlling these weeds due mainly to the size of weeds in the fall.

Stephanie McLain, state soil health specialist with the Natural Resources Conservation Service in Indiana, notes that for some farmers, fall weed control means keeping the field covered with something other than these problem weeds. Bare open land is the perfect place for an annoying weed to start growing. If a field is thickly covered with actively growing cover crops such as cereal rye, annual ryegrass or a combination, a young weed seedling must work a lot harder to survive. 

One crop management plan that can handle fall annual weeds incorporates both a fall-applied herbicide and a cover crop, but you need to understand the herbicide’s impact to the cover crop, McLain says. Even if it’s too late to do it this year, take note in case you want to try this strategy next year.   

Many fall herbicide programs use a combination of broadleaf herbicides to control winter annuals.  This will kill any broadleaf cover crop. In these situations, stick with small grains and other grasses such as cereal rye, annual ryegrass and oats. Find ways where the cover crop can be seeded earlier and have good growth by harvesttime or shortly after. 

Don Donovan, a district conservationist with NRCS, works with farmers who fly-on cover crops, harvest and then apply a fall herbicide. These farmers use grass-type cover crops to get their annual weeds under control, and still get cover crop benefits, he says. If your cover crops are applied aerially, raise the seeding rate to help offset potential competition from winter annuals. 

Fitting together a cover crop system with fall-applied herbicides takes careful planning, McLain says. A good cover crop management plan will help keep it all organized.