Giant ragweed grows rapidly, has an extended period of emergence, and is able to thrive in many environments. These features make it a major competitor with field crops and make it especially difficult to deal with without the benefit of glyphosate.

In recent tests at the University of Tennessee, 12 herbicide treatments were tested for control of ragweed.

Of these materials, glufosinate alone, glufosinate plus glyphosate, glyphosate plus pyrithiobac, and glufosinate plus fluometuron were the most effective.

However, the only combination that showed 90 percent control of giant ragweed without reducing crop yield was glufosinate followed by another treatment of glufosinate.

Davis contends this kind of success in controlling ragweed may encourage growers to rely too heavily on Liberty herbicide and the new Glytol technology.

Unfortunately careful stewardship of farmland isn’t always enough to thwart weed resistance. Davis says.

“In the past few years, we’ve been able to pick up more land and some of it comes from growers who planted soybeans. It seems like they didn’t pay such close attention to rotating chemistry, so we are fighting that battle with ragweed again.

“We are getting more dependent on new technologies to keep these kinds of problems under control.

“One thing we have to do is use this new technology wisely. If we over-use this technology, like we did Roundup, we will probably be facing the same problem, and there’s not any new technology coming along to replace the Liberty Link technology,” he adds.


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“Over the past decade or so, we feel like we’ve gotten a pretty good handle on managing ragweed. The biggest problem we face now is with glyphosate resistant marestail. You can get rid of these weeds, using plenty of products to do so, but a month later, they seem to come back heavier than ever,” Davis says.

“I’m not a scientist, so I don’t know exactly what’s going on with these marestail weeds, but I know the amount of herbicide I applied should have killed them.

“We don’t want to continue spraying glyphosate after glyphosate to control these weeds, because we know what that can lead to,” Davis says.

Last year he planted FiberMax 1944 cotton that includes genetic-driven tolerance to both glyphosate and glufosinate, and says it worked well to get him started on a program to manage resistant marestail.