Lots of sunshine and overall humid weather is having a major impact on crop and weed growth.
While farmers welcome the resurgence in crops, Extension scientists are concerned about weed control, particularly with Roundup resistance showing up some major Minnesota weeds.
"Although it is recommended to target post-emergence herbicide applications to weeds no more than 3 to 4 inches in height, this was not possible in many fields due to wet and/or windy conditions," said Liz Stahl, an Extension crops educator based in Worthington. "Timely weed control has been a challenge this year, particularly where a pre-emergence herbicide was not applied."
How to deal with weeds a foot high and taller is the hot topic across the Corn Belt, she noted.
"Resistance is a real issue," she said. "In Minnesota, we have confirmed populations of glyphosate-resistant giant ragweed, common ragweed and waterhemp. This doesn't mean that all plants of these species in Minnesota are resistant to glyphosate, but the potential is there for resistant populations to exist."
Resistance to other chemistries in a number of weed species including waterhemp also has been confirmed in the state.
"Resistance to multiple herbicide chemistries, or sites of action, can stack up," she added.
To help prevent and manage resistance, Stahl said it is important for growers to diversify weed management practices and identify weed issues early. If weeds were not controlled by a full-labeled rate of herbicide and there were no obvious problems with application of the product, suspect resistance. Use a different herbicide site of action next time (site of action numbers are on most herbicide labels these days). Use mechanical weed control to control escapes. Prevent seed production of suspected resistant weeds. Use full labeled rates and target applications to small weeds. Use a pre-emergence herbicide with residual activity in the future.