Little has dampened the enthusiasm for planting cotton in 2011, except for Southeast and Delta growers who are still trying to figure out how to best manage Palmer amaranth — better known as ‘the super weed’.

At a recent meeting of cotton growers in Savannah, Ga., North Carolina State University Weed Scientist Alan York and Monsanto Herbicide Manager Greg Ferguson discussed the ever-increasing problem of Palmer amaranth with a group of Beltwide cotton farmers.

Greg Fikes, who farms in Brooklet, Ga., says he has been fighting resistant pigweed for five years. “We saw our first real resistance with ALS in peanuts. Then, we got pigweed resistance in our cotton,” he says.

“For those cotton farmers in parts of the Cotton Belt who don’t have glyphosate resistant pigweed, don’t think it can’t happen to you. If you don’t take care of the problem the first year, you will be fighting it every year, and it gets worse and worse every year,” the Georgia grower adds.

Kirby Lewis, who farms about 50 miles from Lubbock, Texas says herbicide resistant pigweed, which they call ‘cheatweed’, is increasing in severity in west Texas.

“I’ve been fortunate in that I haven’t had as big a problem with resistant weeds on my farm, but some of my neighbors are having an ongoing fight with them. Some of them used different herbicides, but after the weeds get 3-4 inches tall, there’s not much you can spray on them,” Lewis says.

Hooded sprayers

Ferguson shared some results Monsanto has had in killing large pigweed with a hooded sprayer. He stressed that killing 2-4 foot tall pigweed wasn’t the intended goal, but delays in testing a new hooded sprayer left them with no choice but to try and kill the large weeds.

“We were using two quarts of Gramoxone, a pint and half of Direx and one-fourth percent of surfactant. The surfactant is important — you don’t want to run a crop oil with this mixture — you get a lot better kill using a surfactant,” Ferguson stresses.

“We get better results on larger weeds when we mix urea products, like Diuron or Direx, with Gramoxone. If you get a good rain within a few days of application, you will get uptake of the urea herbicides by the root system, which will enhance control.”

On smaller weeds, Ferguson says, growers can probably do a good job with a lower rate of Gramoxone.

“In our test field, with the large pigweed, if we burned 80 percent of the weed, within four weeks that weed was dead, using the Graxmoxone-Direx-surfactant mix under a sprayer hood. There were some four-foot tall weeds in that field we didn’t kill, but smaller than that we did a good job with the hooded sprayer,” Ferguson says.

Keep spray nozzles clean

Lewis says one thing he’s tried with some success in west Texas is Diuron applied at lay-by. Keeping our spray tips clean when using Diuron has been a problem, he says. We have to stop every morning and clean the screens out.

Liquid nitrogen in mix

Halls, Tenn., cotton farmer Eugene Pugh says he uses a few gallons of liquid nitrogen in the tank with Diuron to clean the tips. We mix Roundup with Diuron and it seems to work well keeping the tips clean.

Ferguson added that simply cleaning the spray tank and running clean water through it at the end of the day will usually keep the nozzles clean enough to handle gumming problems with urea-based herbicides.

Cover crops

In response to a question about the use of cover crops to manage herbicide resistant pigweed, York quipped, “In my research I don’t like to work with cover crops, because there’s not as many weeds in those fields.”

“There is no doubt cover crops can suppress weeds. The question is what weed suppression advantage am I getting versus some other aggravation that comes into play,” York says.

“Looking at cover crops that get several feet tall, then these are cut and rolled, researchers are getting about 50 percent suppression in Palmer amaranth emergence,” York says.

Recent research at the Tennessee Valley Agricultural Research Station in Belle Mina, Ala. showed that cover crop residue is very effective for controlling pigweed. The rye

was planted at three different dates in late fall and allowed to grow through the winter and early spring before being  killed and rolled prior to planting a cotton crop.

The earlier-planted rye produced greater residue and was most effective at controlling pigweed density (and pigweed biomass). Treatments with winter fallow and traditional tillage (multiple disking) had greater pigweed density (and pigweed biomass).

New herbicides

When asked about new herbicides coming along in the next few years to help manage Palmer amaranth, York says, unfortunately the answer is no.

“If new chemistries that control pigweed are in the pipeline, they are far enough down the pipeline I don’t now about it,” York says. “There are new products and new names that come on the market. Products are pinched together and some new twists on using currently available chemistries are coming and will help, but not a revolutionary new product,” he adds.

“Realistically, the only thing we see on the horizon is 24-D and dicamba resistant cotton. New modes of action are so rare and so expensive to get to the market place that they just aren’t happening.”

Cotton growers attending the meeting were a part of the Monsanto/Deltapine New Product Evaluator program. These farmers grew 20-acre test fields of various research varieties of cotton being developed by Deltapine for distribution in the 2011 season.

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