Be careful when managing herbicides

COLUMBUS – When it comes to managing weeds with herbicides, the worst thing a grower can do is encourage herbicide resistance through overuse or improper management.
Years of mismanaging glyphosate in Ohio crop fields have resulted in widespread herbicide resistance of horseweed (marestail) and a few cases of resistance of some problematic weeds such as common lambsquarters and giant ragweed.
Reduce damage. However, initiating proper glyphosate management now can help reduce further damage, said Jeff Stachler, an Ohio State University Extension weed specialist.
“Glyphosate controls nearly all weeds. That’s why it is such a great product,” said Stachler, who also holds a research appointment with the Ohio Agricultural Research and Development Center. “But because of its effectiveness, growers are overusing glyphosate, which is actually having a detrimental effect on controlling weeds. Our expectations of glyphosate are too high and we should no longer count on glyphosate to consistently control weeds that are too large, greater than 12 inches.”
Reduce applications. Reducing the frequency of glyphosate applications is the most simple and effective approach to reducing glyphosate-resistant weeds, but it may not always be practical for growers based on their field situations. As an alternative, one approach growers can take is properly managing glyphosate, said Stachler.
“If you don’t properly manage glyphosate, you are at a greater risk for poorer weed control, which can result in lower yields, and you are at a greater risk for increased pressure of glyphosate-resistant weeds,” he said. “Proper glyphosate management will not solve the problems associated with glyphosate overuse, but it will greatly improve its negative impacts.”
Bad management. Improper management practices growers tend to fall victim to are: not using the correct rate, applying at the wrong weed size and weed age, applying during the wrong time of the day, using improper boom height, not maximizing rain fastness after an application, not choosing the best additives, paying little attention to environmental conditions and applying during dusty conditions.
Stachler offers the following recommendations to growers when using glyphosate: