While glyphosate resistance continues to monopolize most any discussion of weed control, there are other issues to consider in peanut production, says Eric Protsko, University of Georgia Extension weed scientist.
“Of course we’re spending a lot of time and effort on Palmer amaranth pigweed control for obvious reasons, and in the past couple of years, we’ve made excellent headway in our ability to manage this weed pest,” said Protsko at the 2013 Georgia Peanut Farm Show in Tifton.
“However, we’ve also done quite a bit of work on variety tolerance. Varieties have changed over the years. Just a few years ago, everyone was growing Georgia Green and now we’re not growing it at all.
“My job is to make sure the newer varieties are not any more susceptible to herbicides than others planted in the past.”
And while there’s currently no research or development going on in terms of new herbicides that can be used on peanuts, Protsko is looking at herbicides registered for other crops for their potential fit in Georgia.
“They may or may not ever make it into our recommendations, but if we at the University of Georgia don’t look at it, it probably won’t happen. We can help that process along if a company is interested and there is potential there,” he says.
The key to managing resistant Palmer amaranth pigweed, he says, is to use an integrated approach and not rely solely on herbicides. Use other strategies whenever you can such as tillage, cover crops, irrigation to increase the effectiveness of residual herbicides, planting peanuts in twin rows, and hand-weeding, advises Protsko.
“We’ve got to start clean. Whenever I see a problem, it can usually be traced back to something that wasn’t done properly in the beginning.
“You have to do a good job controlling pigweed at planting and avoid any delays between tillage and planting. Do whatever you can at planting — whether it’s using herbicides or tillage — and start clean.”
Pigweed control programs
The University of Georgia Peanut Team recommends a couple of programs for controlling pigweed, says Protsko.
“One is the Valor/Strongarm program, where we’ve got Prowl, Valor and Strongarm at planting.
“Then, at about 40 days after planting, we apply Cadre. I would suggest you consider adding Dual with Cadre for longer-season control. If for some reason you choose not to use Cadre, you can substitute with Blazer or Cobra in that particular program.
“We know we get great pigweed control with Valor, but we have a lot of issues whenever we get a lot of rainfall around the time of peanut emergence. And there’s no way around that, although we can do some things to help.
“But if we get a lot of rainfall at emergence, we’ll probably see some injury. I would say that probably 95 percent of the time, peanuts will grow out of it and it won’t be a significant problem.”
Because of this injury, some growers choose not to use Valor, he says.
“I think we can still get pretty good control of pigweed with a Dual/Magnum program. With this program, we use Prowl at planting. Then, we go back at 21 days after planting with Gramoxone, Storm and Dual.
“Then, about 18 days later, we spray Cadre and Dual. This provides excellent control which pretty much lasts until August. With this program, we’re using two shots of Dual to help us with pigweed.”
Protsko says the University of Georgia recognizes the state’s top producers each year in the Georgia Peanut Achievement Club, and it’s interesting to take a look at what those growers are doing to control pigweed.
“In 2011, there were 10 growers averaging more than 6,200 pounds per acre. Ten out of 10 of these growers were irrigated, so they could make their residual herbicides work very effectively.
“Seven out of 10 of these top producers bottom-plowed. Nine out of 10 planted in twin rows, and the four herbicides used most by these growers included Sonalan, Valor, Cadre and 2,4-DB. That’s what they’re using to get high yields.”
Most peanut herbicides, with the exception of Strongarm and Valor, were labeled before 2000, and things have changed in the last 13 years, says Protsko.
“We’ve looked at paraquat, sold as Gramoxone or several generics. As growers, you might have sprayed paraquat on your peanuts, and a few hours later you wonder what you’ve done.
“In our trials, we plant a crop, keep out the weeds, and then spray different herbicide treatments. The only effect we’re looking at are the herbicide treatments we impose on the plots.
“In trials conducted in the past three years, we’ve seen no negative yield effects from Gramoxone, Gramoxone/Storm or Gramoxone/Basagran treatments. Most of these plots were planted in GA-06G variety, our most popular peanut cultivar.”
Dual Magnum has been available for more than 20 years, and when it first hit the market there were concerns about injury, especially when there were moisture issues, says Protsko.
“Dual can cause j-rooting in peanuts, but so do other factors. In trials we’ve conducted, we’ve seen no negative yield effects from Dual, PPI, pre, early-post, post, or tank-mixed with Cadre.
“I’m confident that if we use Dual according to the label, unless we have a crazy weather pattern or it’s used at an excessive rate, you should feel comfortable with Dual on peanuts.
Still looking at Classic
“We also continue to look at Classic because there were always some issues with certain peanut varieties. Over the years, we have not had problems with Florida-07, Georgia Greener or Georgia-07W. However, when we’ve used it on Georgia-06G and Tifguard, we’ve seen a slight yield loss associated with it.”
Drift and sprayer contamination continue to be issues for Georgia peanut producers, says Protsko.
“We’ve been spraying a lot of glyphosate for awhile now, and we’re starting to spray a lot of glufosinate or Liberty, so your probability of having potential problems increases.
“Don’t assume the 2 gallons left in the bottom of the sprayer that looks like water is water. It could be a mixture of something.”
The concern for the future, he says, is what’ll happen to peanuts if growers adopt 2,4-D and dicamba-resistant technology for cotton and soybeans.
“If we know the rate that was used, we can probably figure what the yield loss will be. Most of the problems we’ve seen have been with sprayer contamination.
“If you’ve been spraying cotton and using glufosinate, I encourage you to make sure the tank is clean before spraying peanuts. Peanut yield loss from glufosinate can be fairly significant depending on the time of year.”
While there are no new herbicide products for use on peanuts, researchers are looking at products like Warrant and Fierce to see if they have a potential fit in peanuts, says Protsko.
Growers should continue to be vigilant in avoiding resistance issues with various herbicide classes, he adds.
“Now that about 50 percent of our cotton is being treated with Liberty, we have to manage that herbicide to avoid resistance.
“If you’re a cotton or soybean grower, and you’re anticipating 2,4-D and dicamba-resistant technology, you need to know that those herbicides by themselves are not enough.
“We need glufosinate to help us with pigweed control. If we lose that now before the technology becomes available, we’ll be in trouble.”
Valor and Reflex have the same mode of action, so growers need to use caution when using those herbicides, says Protsko. “Dual and Warrant are in the same herbicide family and have the same mode of action, so we also have to be careful with these materials. Protect these herbicides at all cost.”
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