January 3, 2007 | By: Laura Skillman

So far, Kentucky has only a few weeds that have developed resistance to chemicals used to control them, but vigilance and proper use is essential to ensure that control measures will continue to be effective.

There are seven weedy biotypes that have been confirmed to be resistant to at least one chemical control in Kentucky. Other control measures are still available to combat these pesky weeds.

“Kentucky farmers have done a pretty good job, but we are slipping. We’ve got to be on our toes,” said Jim Martin, weeds specialist with the University of Kentucky College of Agriculture. “I have to believe that the reason we don’t have the problems of some of our neighboring states is the cropping rotation that we are using – corn, wheat and soybeans. That rotation to some extent has helped to minimize our resistance. Generally, where we see those problems is where we don’t see this kind of a rotation.”

Farmers are moving away from the traditional crop rotations somewhat because of strong prices for corn, so other options will be needed to control weeds.

Heavy reliance on the same chemistry can result in shifts in weed populations that are resistant to the product. That doesn’t mean abandoning a product that has long proven successful, Martin said. It does mean respecting the product, using it in the appropriate rates and not using it as the sole source of control year after year.

Finding the right mix of products that can ensure proper weed control is an important tool in keeping as many products available as possible to combat weeds.

In Kentucky the majority of soybeans produced are “Roundup Ready©,” meaning they are resistant to the herbicide glyphosate, allowing the chemical for weed control while not damaging the beans.

Using a residual herbicide prior to planting can be helpful in minimizing the weed competition, especially for corn early in the growing season, he said. It also buys more time before the corn will need to be sprayed with glyphosate to maintain the weed control.
In 2006 volunteer corn was a problem in many soybean fields and will likely be a problem in 2007, especially if it is in a field where Roundup Ready© corn is being followed by

Roundup Ready© soybeans, he said. Using glyphosate on the crop will not kill the corn and another herbicide will have to be used to kill it. There are options to control volunteer corn in Roundup Ready© soybeans if glyphosate cannot be used. Controlling volunteer corn is important because of the detrimental impact it can have on soybean yields.

“The sooner it can be treated the better, generally within two to four weeks after emergence,” he said.


Jim Martin, 270-365-7541, ext. 203