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Weed ID, herbicide spectrum keys to peanut weed control

LUBBOCK, Texas - When it comes to controlling weeds in peanuts there is no substitute for good information.

“Know your weeds,” says agronomist Peter Dotray, who has joint appointments with Texas Tech University, the Texas Agricultural Experiment Station, and Texas Cooperative Extension, all based in Lubbock.

“Peanut farmers have several weed control options,” Dotray said during a recent peanut production and marketing seminar, sponsored by the Texas Cooperative Extension Service and the Texas Peanut Producers Board.

“Know the herbicide options and what each of them can and cannot do,” Dotray said. “Learn their weed control spectrum, the length of residual control, potential injury to peanuts and rotational crops.

“Also, determine if your sprayer is calibrated to deliver the expected carrier volume to provide uniform and thorough coverage to the target and to minimize spray fines that are susceptible to off target drift.”

Dotray said the typical peanut weed control program includes a preplant incorporated application of a yellow herbicide. After the preplant herbicide, growers often use several cultivations and a herbicide application applied post-emergence. These post-emergence treatments may include Blazer, Basagran, Storm, Pursuit, Cadre, 2,4-DB and combinations of 2,4-DB plus other herbicides.

He said Prowl, Sonalan and Treflan remain good options for preplant incorporated weed control. “These herbicide are the backbone for effective weed control,” he said, “but we still get questions about crop injury.

“The key is rate and incorporation method. A double-pass method of incorporation is recommended on most labels, but a single-pass is most commonly used. The better the herbicide is mixed and uniformly distributed, the better the weed control. We have a lot of data to support the weed spectrum (controlled) and peanut crop tolerance.”

Dotray said as more peanut farmers switch to reduced tillage systems they ask about potential weed control and crop injury. “Our 2003 data showed that Prowl in reduced till systems, surface applied and followed by three-fourths to an inch of water, was effective. But that’s one year’s data on one location. We will follow up on that study.”

He said Dual Magnum and Outlook showed good activity on yellow nutsedge but not purple. “We saw some peanut injury following pre-emergence application. We also made a post-emergence application to minimize or eliminate peanut injury and these herbicides still provided effective control of yellow nutsedge.”

Dotray said Strongarm is no longer available for peanuts in soils with a pH of 7.2 or greater.

Valor is a relatively new peanut herbicide, labeled for peanuts in 2001, but it has been researched for nearly a decade. “I’ve looked at Valor for several years. A 2 to 3-ounce rate provides good residual on several tough broadleaf weeds, including annual morningglory.”

Residual activity lasts four to six weeks, he said. “After that, we may see flushes of escaped weeds, and we need an additional application. Valor applied delayed pre-emergence injured peanuts in 2003. Applications must be made within 48 hours after planting or stunting and a bit of yellowing may occur.”

Dotray said cotton farmers sometimes plant Spanish peanuts in hailed-out cotton and he tested injury to peanuts from the cotton areas that were treated with several pre-emergence herbicides.

“Slight peanut injury was observed in Dual Magnum-treated plots. By the end of the year, injury was not apparent and we saw no decrease in yield. We also saw slight visual injury following Staple.”

Dotray said replanting cotton in the lost acreage also resulted in some injury, but only from Dual Magnum. “In many cases, cotton plants did not recover, and we saw a decrease in lint yield.” He noted that this type of injury might be the result of the sandy soil where these studies were conducted.

Dotray tested reduced rates of Cadre and Strongarm for ivyleaf morningglory control. “Cadre is a good High Plains herbicide but rotation restrictions with cotton limit its use. Strongarm also looked good when applied postemergence, but is not currently labeled for this type of application. A tank-mix of these two herbicides at reduced rates or a tank-mix of reduced rates of Cadre and Dual Magnum or Pursuit and Dual Magnum also showed promise,” he said.

“But that may limit a farmer’s ability to rotate to cotton.”

Dotray said that several tests were conducted in the High Plains, the Rolling Plains and South Texas with other combinations and reduced rates. The key, he said, is to maintain effective weed control at reduced costs.”

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