By Mark Loux, Extension Weed Management Specialist

Ohio State University Extension weed management specialist Mark Loux shares some tips and considerations for weed control as corn and soybean harvest winds into gear.

1. Cressleaf groundsel, which is poisonous to livestock, has caught some hay and livestock producers by surprise when they discover it in late spring in hay or pasture. Some hay producers have had to discard hay from first cuttings due to an abundance of this yellow-flowered weed. Cressleaf groundsel is a winter annual weed that is easily controlled in the fall, when in the rosette stage, in most crop situations. Take time to scout fields this fall to determine whether cressleaf groundsel is present, especially in new summer seedings or fields with a history of this weed problem.

2. Check the C.O.R.N. archive for articles on burndown options for no-till wheat and fall herbicide treatments prior to corn or soybeans. Not much has changed and these should generally be current still.  With regard to fields where the tentative plan is to plant Enlist and Xtend soybeans, we suggest continuing with fall herbicide treatments to minimize the variability in spring marestail burndown that can occur with both 2,4-D and dicamba.

3. For growers with waterhemp, reminder to take advantage of a $50 service offered by the University of Illinois to screen populations for resistance to glyphosate and site 14 herbicides (Flexstar, Cobra, etc). Where Roundup Ready soybeans will be planted in future years, these are the only POST options for waterhemp, so it’s essential to know whether they are still effective. This involves the overnight shipment of leaves, not seed, which is still possible but time is running out. See the July 26 edition of C.O.R.N. for more information.

4.  Keep an eye out for waterhemp and Palmer amaranth when harvesting, with the goal of preventing further spread if found. Where plants or patches of these are encountered, think twice about just harvesting right through them. Doing so will disperse seed more widely throughout the field being harvested, and also contaminate combines with the possibility then of spread to other fields. We've seen all of this occur in our investigations of Palmer amaranth. The wiser choice where these weeds are encountered, or where additional help with identification is needed — avoid harvesting through the weeds for now, get positive identification, and remove them by hand prior to harvesting the crop in that area.