Gunsolus says spring was tough on pre-emergence herbicides
Janet Kubat Willette
Date Modified: 12/01/2009 11:37 AM
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Agri News staff writer
WASECA, Minn. -- Spring 2009 was rough for pre-emerge herbicides, Jeff Gunsolus said at a June field day at the Southern Research and Outreach Center in Waseca.
Gunsolus, an University of Minnesota Extension weed scientist, talked about herbicide research trials under way and also glyphosate non-performance issues.
If a farmer's strategy is to start early and end early when it comes to herbicide application, it's difficult to have a total glyphosate system, Gunsolus said.
Farmers must allow time for scouting and non-glyphosate resprays, he said. Scouting should begin 10 to 14 days after the first glyphosate application, with farmers checking for plants that survived the application.
Check to see if there is a single surviving species. Is the surviving weed species the same species that survived in the same area of the field in previous years? Has the same chemical been used on the same field for several years?
Farmers should give more consideration to pre-emerge and early post-emerge herbicides, which allow more flexibility if a grower gets busy or weather prohibits timely post-emerge applications.
Chemical diversification should also be considered as it is essential to keeping the Roundup Ready technology viable into the future, Gunsolus said.
Biotypes of giant and common ragweed and common waterhemp in Minnesota have been confirmed as glyphosate-resistant.
"Both species appear to be resistant to approximately four times the labeled use rate of glyphosate," Gunsolus said.
Glyphosate tank mixes was one of the research projects Gunsolus worked on this year. Other research projects included new products for weed control in corn and soybeans, Liberty Link soybeans and Optimum GAT corn and soybeans.
Issues under consideration included alternatives to atrazine, Gunsolus said. Atrazine replacements and the effectiveness of atrazine at low rates in tank mixes were evaluated.