If your crops were drought-stressed this year – and whose weren't – it is a good idea to have a conversation with your seed dealer, crop specialist or agronomist before you plant wheat this fall or row crops next year.
Jenny Goodman, a specialist with Dupont Crop Science, talked about herbicide carryover risk at Husker Harvest Days on Wednesday. She says herbicides from different chemical classes have different systems of degradation and heat and drought can increase the risk of herbicide carryover, even if you followed label directions and planting interval recommendations.
Some chemistry classes require moisture to break down completely, she said. Others need microbial activity in the soil to degrade. In both of those instances, a drought-stricken field can have carryover herbicide.
"You just have to make sure you go to your local person, talk about what combinations you may have used on a given field and let them help guide you through decisions about how any carryover risk may affect your normal rotation," she said.
Herbicides with residual action and a combination of herbicides with different modes of action are often recommended to farmers concerned about weed resistance, but can be of greater concern when it comes to carryover.
Chemistry classes that break down by chemical hydrolosis are the least likely to cause carryover problems, she said, because they are affected more by soil Ph than by the need for moisture. They break down faster in slightly acidic soils, she said.
"I advise people to make sure they are basing the planting decision on the chemistry class of their herbicide, not its mode of action," she said. "Two herbicides with the same mode of action can be in different chemistry classes. And two herbicides from the same chemistry classes can have different modes of action."