There Are Answers for Giant Ragweed Control

Choose herbicides and strategy that work for you.

Published on: Dec 3, 2010

Each month in Indiana Prairie Farmer you'll find a column marked Crops Corner. A question asked by a farmer is addressed to a panel of three certified crops advisors. They belong to the Indiana Certified Crops Advisor group. The CCA designation means that they are continuing their education by taking courses and attending meetings so that they stay abreast in the latest in crop production techniques.

The January issue will feature a question about giant ragweed control. Here's a sneak preview.

A farmer complains that a light rate of residual and glyphosate didn't take out giant ragweed in corn or soybeans. He's concerned the ragweed is resistant, and if they are, what he should do.

CCA columnists rotate on a three-month basis. The joint project between Indiana CCA and Indiana Prairie Farmer has been ongoing for more than five years now. Jeff Nagel, an agronomist with Ceres Solutions, with Nagel based near Lafayette, has been a frequent columnist.

The problem with giant ragweed is that it's competitive, plus you get multiple flushes with rainfall events, Nagel says. And yes, there is some resistant giant ragweed. On the plus side, it's a weed where the seed bank can be reduced over time. "The secret is to keep it from setting seed," he says.

For corn, Nagel suggests starting with a soil-applied herbicide. Utilize a reduced rate of a grass/broadleaf premix, and add additional atrazine. The extra atrazine will help on giant ragweed control. Good choices include Corvus, Lexar/Lumax and SureStart, although there are others, he notes.

Then the crucial part is to apply glyphosate at one and a half times the normal rate, not the normal rate or even a reduced rate below that point. If you're going after a weed that your herbicide has a tough time killing anyway, you certainly shouldn't try a reduced rate and expect big-time results.

If you want, you can mix a single application rate of glyphosate with Status or another broadleaf herbicide, he adds. Multiple passes of glyphosate without anything in the mix to help it probably won't be a benefit.

For soybeans, Nagel would go with Scepter, Canopy DF, Envive, Valor XT, Sonic or some other good, soil applied herbicide. Again, he would opt for one and a half-rate glyphsoate, and hit weeds at 4 inches to 6 inches.

There aren't many good tank partners in this case for soybeans. The biggest thing is to get the ragweed before it gets too tall, he notes.

Take a look at the January issue for ideas on the same question form other CCAs.