When Monsanto’s Bollgard II XtendFlex cotton system enters the market—possibly as soon as 2015, pending regulatory approval—the technology will offer “another valuable tool” to improve weed control efficiency, especially in light of growing concern over herbicide resistant weed species.

“But it is no silver bullet,” says Monsanto’s John Everitt. “We need to use pre-emergence herbicides, too. We know we have herbicide-resistant weeds in West Texas, so farmers who have relied exclusively on glyphosate need to add additional modes of action into their program.” 

Everitt, speaking to a group of farmers at a recent Deltapine field day near Seminole, Texas, said Monsanto’s new weed management system—transgenic varieties that include tolerance to both glyphosate and dicamba herbicides in soybeans and glyphosate, dicamba and glufosinate in cotton —will offer farmers a new option to manage resistant Palmer amaranth—and other species—but insists that producers must follow a “systems approach,” to control weeds in cotton.

Farmers also heard about two new varieties, scheduled for release for 2014, that are resistant to root-knot nematodes.

Everitt said new weed control technology will allow over-the-top applications of a glyphosate and dicamba pre-mix to increase weed control spectrum, including glyphosate-resistant pigweed.

 

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The new products are designed to provide more consistent, flexible control of “resistant- and tough-to-control weeds” and help maximize yield potential.

Going back to pre-plant incorporated or pre-emerge herbicide applications is an important part of the system. Materials such as Treflan and Prowl will play a crucial role. “It’s cheap insurance,” Everitt said, “and effective against pigweed. But producers have to get it incorporated.”

Applying Prowl one to two weeks before planting with about three-fourths inch of irrigation is one good incorporation method. Farmers can chemigate with Treflan.

From there, growers may choose, based on field history and previous weed pressure, to add other residual herbicides and then spray over-the-top with new Roundup and dicamba products. “We will offer two new chemistries in 2015,” Everitt said, “that include glyphosate and a low-volatility dicamba (Roundup Xtend and XtendiMax).” These will be part of the Roundup Ready PLUS weed management solutions program.

But new products come with new application parameters. Managing drift and maximizing on-target application is a crucial part of the system and requires that farmers follow application requirements including:

  • Use low volatility formulations.
  • Select nozzles that produce very coarse or ultra coarse spray droplets.
  • Wind speed should be between 3 and 10 miles per hour.
  • Boom height should be 20 inches above the crop canopy.
  • Maintain a spray buffer as required by label to protect sensitive areas.
  • Use a drift reduction agent.
  • Apply at least 10 gallons per acre.
  • Triple rinse for adequate tank clean out.
  • Maintain a ground speed less than 15 miles per hour.
  • Spray when weeds are small—less than 4 inches.
  • Use sensitive crop registries such as DriftWatch and others.
  • Use residual herbicides to improve resistant weed management.

Everitt said volunteer cotton control should not be a factor with addition of dicamba to the system. “Most farmers are not spraying dicamba to kill volunteer cotton. Use gramoxone or cultivate,” he said.

He also said that Bollgard II XtendFlex cotton is “not cross-tolerant to 2, 4-D,” so growers cannot spray 2, 4-D on Xtend cotton.

Nematode Resistance

At the other field tour stop, Monsanto’s Jorge Cuarezma, Monsanto technology development, said root knot nematodes cause severe crop injury and also exacerbate Fusarium wilt problems in cotton. Seed treatment control, he said, often breaks down after a few weeks, especially in areas of high nematode pressure.

Nematode infection symptoms include yellowing of leaves, stunting of the plant and taproot, tell-tale galls or knots on the tap and lateral roots, along with a lack of secondary hairs on the roots. “Because root knot nematodes attack the root system, reducing the plant’s ability to take up water and nutrients, symptoms are most noticeable during periods of stressful environmental conditions. Lighter soils, such as sand that are more susceptible to nutrient leaching, are more likely to show visual symptoms of damage.

“With heavy populations, we need a resistant host,” Cuarezma said. Resistant varieties, he added, show significantly fewer galls on the roots and disrupt nematode reproduction. “Breeders are finding resistant genes in cotton plants. Deltapine’s two experimental nematode resistant varieties—13R341 and 13R347— are part of Monsanto’s New Product Evaluator (NPE) program and are candidates to be on the market for the 2014 season.” Those are research numbers and will change when the varieties are released.

Cuarezma said nematodes obstruct the vascular system of plants and hinder growth. Nematode infection also has an effect on Fusarium wilt and limits yield and performance of the cotton plant.

The number of nematode eggs on resistant cotton variety roots is “much less and the resistance reduces the number of root-knot nematodes in the soil profile,” he said.

Monsanto’s Dave Albers said growers need varieties that are not only resistant to root knot nematodes but “are also good performers where there is no nematode pressure.”

The new varieties will be mid- to full-season, and 347 is slightly later than 341.

Ongoing tests this season also evaluate nematode injury, based on soil moisture readings from the root zones. “We hope to put a value on nematode traits,” Albers said. “And we hope to extrapolate that back to yield.” Marker-assisted breeding helps isolate the genes linked to nematode resistance. “These are breeding traits, not biotech.”

“We hope to launch these varieties where they will best fit,” Cuarezma said.

“We need something like this in this area,” said Manda Anderson, Texas AgriLife Extension integrated pest management specialist. “I think nematode damage is right behind Verticillium wilt, which only comes in wet years. With a high level of nematode infection, seed treatments tend to break early.”

 

Also of interest:

Across the Sunbelt, herbicide resistance changes production options

Weed resistance now an issue in Texas

Prevention is best strategy for resistant weed management