Purdue weed scientist: Late-season herbicide applications may be ineffective
By: Emma Hopkins
WEST LAFAYETTE, Ind. – For farmers seeing weeds in their crop fields this late in the growing season, hand-rouging and pulling them by hand may be the best way to remove them, more so than using a herbicide, a Purdue Extension weed scientist says.
“The majority of weeds in corn and soybean fields are much higher than the ideal 4-8-inch height, and herbicide applications are only going to provide marginal
control at best,” said Travis Legleiter, Purdue Extension weed scientist.
The most common weeds that may not be under control at this time in the season are Palmer amaranth, common waterhemp, giant ragweed and marestail. If herbicides are repeatedly applied to these larger, full-grown weeds, the offspring are more likely to be herbicide-resistant, Legleiter said.
“Although it is human instinct to try and spray something and do something about the tall, ugly weeds in our fields, we may be better off not spraying and not selecting for resistant biotypes,” said Legleiter.
Another risk that comes with spraying herbicides late with residual activity specifically is the possibility of the herbicide carrying over into the winter and spring, which can be potentially damaging to those crops.
“Hand-rouging and hand-pulling may be our only options at this point and the most effective, even though it will be the most time- and labor-intensive option,” Legleiter said.