Bob Scott, weed scientist at the University of Arkansas, says 2006 was generally a good year for weed control, but Roundup (glyphosate) failed in burndown applications to control resistant horseweed in several counties.
“These were in a lot of counties where glyphosate-resistant horseweed hasn't been a problem in the past, but we found out that it's moving south and west, radiating out from Mississippi and Crittenden counties where it first became a problem,” Scott says.
Herbicide applicators had to contend with windy, challenging conditions, he says. As a result, when they tankmixed 2, 4-D and dicamba and “tried to do the right thing for resistant horseweed, they still had poor control in some areas.”
Scott expects glyphosate-resistant horseweed to be a “big problem” next year. He says the university will test burndown herbicide applications with residual herbicides in the fall.
“We're looking at Valor, Prowl and other herbicides to provide residual control of horseweed so we can try to get this thing in check,” he says. “Once it gets into a growing crop such as cotton or soybeans, it can be difficult to control. We found that out this year.”