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Still Time to Clean Up Nasty Ragweed in Beans

Still Time to Clean Up Nasty Ragweed in Beans

Other options for glyphosate-resistant weeds.

OK, so the deck was stacked against you. It turned wet when you should have been spraying soybeans. Weeds got taller than you like. And to top it all off, your chemical dealer is pretty sure some of the giant ragweeds you're fighting in a couple of fields are resistant to glyphosate. That means spraying the field with glyphosate likely won't do any good, at least not on the giant ragweeds that are threatening the fields. It would only serve to make someone mad, likely you, not the weeds!

Betsy Bower, an agronomist with Ceres Solutions, based in Terre Haute, says all is still not lost. Bower is a member of the Indiana Certified Crop Adviser's Association. There may still be time for a rescue treatment that can knock down those ragweeds.

Bower would be motivated to try because of information she's seen that documents how devastating ragweed can be in soybeans. According to one report she read from Michigan State University, one giant ragweed plant per 100 square feet of soybean field can cut yield by 52%. That's a 10 by 10 area, about the size of a small bedroom. According to the study, one giant ragweed plant would be all it takes to devastate the field. That's mind-boggling, or as the 15 and 16-year olds are into today, that's baffling!

Bryan Overstreet, Purdue University Extension ag educator in Jasper and Pulaski Counties, isn't so sure there's still time for an effective rescue application. He thinks that at very least, the window may be closing quickly.

Bower says the best products to consider at Flexstar GT, once known as Flexstar, and Cobra. The old reliable Cobra product hasn't changed since it was introduced in the pre-Roundup Ready days.

However, consult the labels carefully. There are restrictions as to when they can be used. Labels may talk about weed height. If 36 inches is the maximum labeled weed height, some farmers with out-of-control fields may need to head for their sprayers soon.

Sometimes labels specify that the product can only be used if soybeans are in certain stages. If beans are 100% flowering and pods are forming, it may be too late for the application.

"Cobra actually has a label for up to 45 days before harvest," Overstreet says. "But you need to check the giant ragweed stalks themselves. Stalk borers work on them in some cases. If insects have already burrowed into giant ragweed plants, it may be much harder to get effective control."

Plus, control is a relative term. Expect suppression, not total weed control at this stage in the game, he advises. Also expect leaf burning from the herbicide applications.

TAGS: USDA Extension
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