There have always been two objectives to weed control. The first is obvious: keeping weeds from taking moisture and nutrients from this year’s cotton. The second is less obvious, but equally important: keeping weeds from going to seed and affecting next year’s crop.
A weedy field this year is more apparent and more immediate, but in this age of growing resistance to herbicides, it is increasingly important to control weeds and keep them from going to seed.
The situation is best exemplified in the Palmer amaranth species of pigweed that has developed resistance to glyphosate in some areas.
“Morningglory is our most common weed and it’s the driving force behind the use of ET at layby, but the resistant amaranth is the one we need to watch for,” says Dr. Stanley Culpepper, Georgia Extension agronomist. “Each resistant weed that makes it to harvest can shed thousands of seeds, and those seeds can stay in the soil for years.”
ET is a broad-spectrum herbicide from Nichino America.
Digging in the Dirt
There are herbicides that are still effective against resistant pigweed, but in some cases growers have resorted to digging up weeds by hand. “We have a little bit of that here,” says Howard Cross, a cotton grower in Pinehurst, GA. “We’ve had to go out and dig up a few glyphosate-resistant weeds by hand.”
Not everyone has to go that far, says Culpepper. His specific recommendations are available at www.gaweed.com, or at Georgia Extension offices.
Every weed has the potential to develop resistance, and within each species is enough genetic diversity to ensure that at least a percentage will be naturally resistant to a particular herbicide. If those weeds are allowed to survive, they can pass the resistance on to the next generation.
Doing a solid job at burndown, including a second if-necessary burndown application, is the way to start an effective resistance management program. After that, it’s back to basics – using a residual herbicide at planting and a post-directed herbicide at layby.
ET Phone Home
ET at burndown, postemergence or at layby is an excellent tank-mix partner if a grower has bindweed, morningglory, lambsquarter or pigweed in his field, says Ricky Sloan, of Helena Chemical in Moultrie, GA. “ET does a good job on those weeds, plus it heats up the tank mix,” he says.
Sloan avoids Roundup altogether at layby and recommends 1 quart of MSMA, 0.5 to 0.75 ounces of ET per acre, and a quart of mentholated seed oil per 100 gallons of water. If growers want to add a residual herbicide, he recommends adding a quart of diuron per acre. Sloan says these tank-mixes combine the strengths of each herbicide, while avoiding overuse of glyphosate.
The goal is to have a clean field at harvest so that weeds don’t go to seed. Ideally, after layby the canopy will closes and weed seed cannot germinate. But in dry years, canopies may not close and late-season weeds can cause problems.
If that’s the case, then ET can again provide some options. “ET is also registered as a defoliant, so if I see any morningglory, I add ET to the tank mix,” says Cross. “It gives good defoliation, and it keeps the morningglories from going to seed.
Editor’s note: Some information for this story was provided by Nichino America.
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Palmer amaranth produces millions of seed.