Pre-plant and pre-emergence herbicides for cotton work well on soil with up to about 5 percent organic matter. As the organic matter gets higher than about 5 percent, the effectiveness of these herbicides drops off rapidly. Valor is the exception. It will work up to around 10 percent organic matter. 

Cotton growers in the Blacklands of North Carolina, where most soils are greater than 5 percent organic matter, will have a real problem if Palmer amaranth spreads to that area. With the current technology, growers must depend heavily on soil-applied herbicides to control Palmer amaranth.  Options for growers in the Blacklands will be very limited.

Don’t make the same mistake twice!

The use of glufosonate tolerant cotton was fairly widespread in North Carolina in 2010 and some experts contend as much as 65 percent of cotton in the Tar Heel state next year will have the glufosinate tolerant gene in it.

“The first thing you need to understand, if you’re planting glufosinate-resistant cotton, is that you are putting out Ignite and Ignite is not Roundup. Timing will be critical and to get the kind of control you need, you have to get this herbicide out before Palmer amaranth gets more than 3-4 inches tall.

“There’s always going to be somebody who claims they killed pigweed 14 inches tall with Ignite. Well, good for you — you’re lucky, but the optimum size for glufosinate to kill pigweed is still 3-4 inches,” York says.

“Perhaps the most important thing growers need to keep in mind when they plant glufosinate tolerant cotton is that over a relatively short period of time we took Roundup Ready, the best weed management technology we ever had, and we blew it. Glufosinate technology is good, and there is nothing coming down the pike for a few years, so we cannot afford to blow this one by over-using it,” York adds. “We really need to focus on a strong resistance management program in glufosinate tolerant cotton”.