Crop Scene Investigation - 38 Solved: What's behind the weed escape in Scott's soybeans?

Monday, April 2, 2012

by BERNARD TOBIN

Weed resistance was the cause of Scott's foxtail escapes featured in our March 2012 issue. What agronomist Pat Lynch found in his field was Group 2 resistant foxtail.

The clue to the mystery was contained in the dead and dying weeds that could be found beside the green, vigorous foxtail plants.  A close look revealed that many foxtail plants had turned red and purple and were dying – the classic death symptoms of foxtail that are not resistant to Group 2 graminicides.

Lynch believes the resistant foxtail were likely carried into Scott's field in 2007 by his custom combine operator and it took several years for the population to grow before becoming obvious.

Lynch explains how the foxtail population probably multiplied. In 2008, Scott grew soybeans and there was likely a smattering of resistant weeds in the field that he did not notice. In 2009, the field was in wheat and the foxtail did not germinate because of competition; they just sat there.

In 2010, the corn herbicide provided control, but when Scott went back to soybeans in 2011, he again used a Group 2 herbicide and it couldn't control the growing population of resistant foxtail.

Lynch says it's important for growers to do a good job of scouting their fields. "Or better still, get someone to scout it for you. That's because people who are scouting fields regularly can do a much superior job than most growers.

"When you are scouting and there is only one weed species left, and it was on the label of the product you were using, big bells should go off," says Lynch. "You then have resistance to whatever product you used."

Congratulations to Bill Ford, Grey Highlands, for his correct answer.

CSI will return this fall. BF