Grapes are among a few crops that are ultra-sensitive to 2,4-D in particular. Dow, which will market Enlist herbicide, which contains genes making cotton and other crops tolerant to 2,4-D and glyphosate, contends Colex-D technology will make the new formulations of 2,4-D much less prone to drift and become a problem on non-targeted crops.

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Grapes are sensitive to 2,4-D because of the way plants metabolize the active ingredient in leaf tissue. Multiple studies have shown grape plants can retain Dichlorophenoxyacetic acid in the leaf tissue for three weeks or more. 

Grapevines may be injured by phenoxy-type herbicides throughout the growing season, but are most vulnerable in the first half of the growing season, when shoot tips are actively growing.

Colex-D technology is composed of new 2,4-D choline, which in combination with 2,4-D, results in herbicides with ultra-low volatility and minimized risk of moving from a target crop to a non-target crop in nearby fields.

Frame says it will be important for growers to fully understand what rates, sprayer settings, nozzle size, wind direction, wind speed and other variables exist before using these new herbicides. “We are being told the new Colex-D technology makes these materials much less prone to drift and volatilization, but it is important we know the new guidelines under which these materials can be safely used,” the Virginia Tech scientist says.

Of particular concern in the Upper Southeast will be in counties in northwest North Carolina well into southwest Virginia, which is an area home to some grape production and some of the larger remaining tobacco operations.

Tobacco, especially in the seedling stage, is extremely sensitive to 2,4-D. How these new herbicide combinations are used on crops that are adjacent to high value crops like grapes and tobacco will be a significant challenge to farmers in the area.

Despite opposition from groups like Save Our Crops, which represents more than 2,000 U.S. farmers, Dow expects to get full registration for Enlist on a number of crops for the 2014 and 2015 growing seasons and beyond.

The contributions of 2,4-D (Dichlorophenoxyacetic acid) to the growth of the row crop industry in the Southeast are well documented.