Boost Weed Control and Increase Wheat Yields

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Known globally as the most successful weed species in terms of herbicide resistance evolution, it's little wonder Italian ryegrass continues to challenge U.S. wheat growers.

When weed scientist Larry Steckel first arrived at the University of Tennessee 20 years ago, he saw farmers control Italian ryegrass fairly well with ACCase inhibitors (Group 1). "I've seen it become resistant to Group 1, then it resisted some Group 2 ALS inhibitors, then Group 9 glyphosate," he says. "It's pretty much resistant to many different herbicides, and it doesn't have trouble evolving resistance to new chemistries."

Depending on your location, this annual ryegrass species is resisting control by herbicide site-of-action Groups 1, 2, 9, 10. There is also Italian ryegrass breaking through applications of Group 15 chemistries in the Pacific Northwest, and early indications of resistance to Group 22 (paraquat) have been discovered in North Carolina.

SIMILAR GROWTH PATTERN

Weed biology of this winter annual species adds to control challenges by germinating and emerging in the fall in a staggered but continuous pattern, slowing in winter and reaccelerating in spring.

Kansas State University weed scientist Sarah Lancaster says it's become a problem weed for wheat growers that is well adapted in southern and eastern Kansas since it emerges and grows right with the wheat crop. "This Italian ryegrass also can more easily develop herbicide resistance and is very competitive with our wheat crop, reducing stand and yield," she adds. "My counterparts in the southeastern U.S. consider it a top concern due to herbicide resistance."

Steckel has watched the dominance of this herbicide-resistant ryegrass build in the heart of the Mississippi Delta a decade ago, then work its way north into Tennessee and Kentucky. "Since we're a no-till state, this weed has fundamentally changed how we use burndown programs since glyphosate is becoming less effective every year," Steckel says.

In Texas, Sam Rustom, FMC technical service manager, sees different pockets of infestation levels -- from extremely severe to slowly building levels of Italian ryegrass. He sees and hears stories of resistance issues from many areas of the state. "While Palmer pigweed may get all the attention at grower meetings, Italian ryegrass has really become one of the most difficult to control weeds ever," he adds. "And we haven't been fighting it near as long compared to growers in the Mid-South, Mississippi and Arkansas."

PROPER WEED ID

Lancaster always emphasizes correct weed identification with farmers so Italian ryegrass isn't confused with the easy-to-control cereal rye, which is often planted as a cover crop. They are very different plants; Italian ryegrass has narrow, shiny leaves, and cereal rye leaves are broader. In addition, Italian ryegrass grows shorter and more compact with tiny spikelets arranged alternately along the stem, while cereal rye is taller with a distinct spike like wheat. Oklahoma State University Extension has compiled some excellent photo IDs of the Italian ryegrass. Visit https://extension.okstate.edu/…

STAND AND YIELD LOSS

Wheat acre economics can take a big hit when herbicide-resistant Italian ryegrass invades a field -- causing yield losses as high as 50% and upwards to 100% in severe cases. Oklahoma State University research has shown a 20% yield loss with 15 plants per square foot. "And foreign matter dockage at the elevator can be high since it's difficult for a combine to separate ryegrass seed from wheat," Lancaster says.

Cultural tools used to reduce Italian ryegrass vary in effectiveness. Lancaster reports that rotating wheat with a broadleaf crop like soybeans in Kansas offers a better chance to control it with herbicides. However, in Tennessee Steckel says crop rotation is failing. "We see herbicide-resistance issues in all crops, so controlling ryegrass in different no-till crops with different herbicides is really not a good option in Tennessee," he says.

Other potential control methods like tillage and burning come with erosion and environmental issues. "The Australians are using harvest weed seed control equipment on combines that destroy the seed. It is working to reduce the weed seed bank in the soil, so that will hopefully be a combine option offered in the future," Lancaster says.

BEST CONTROL OPTIONS

According to Steckel, reducing the first two early flushes of Italian ryegrass that emerge with winter wheat is critical to a strong wheat stand and minimizing yield loss. "When it comes up later in the spring, it's less competitive with the crop, so keeping it from coming up is the best strategy."

Steckel and Lancaster believe pyroxasulfone applied in a delayed preemergence application can work well to reduce Italian ryegrass emergence in wheat, but timing is critical. "You want the shoots and roots of the wheat out of the seed and somewhat established before you apply pyroxasulfone, so timing is tricky," Lancaster says. "We see growers using Anthem(R) Flex herbicide that adds carfentrazone, a group 14, to help control weeds already emerged."

Steckel has seen effective control of Italian ryegrass with pyroxasulfone. "Residual control is a must because our main management goal is to keep ryegrass from ever coming up," he says.

FMC's Rustom adds that planting wheat into moisture and checking the fields regularly are his top recommendations for successful Italian ryegrass control. "Optimal timing for an Anthem Flex herbicide application occurs when the field achieves 80% wheat germination with a 1/2-inch shoot. The sooner you catch those ryegrass seeds germinating, the better the control," he says.

Like any preemergence product, Anthem Flex herbicide needs 1/2 to 1 inch of rain within 1 1/2 to 2 weeks of application for effectiveness, using a 3 to 3.5 ounce per acre rate, depending on soil texture and organic matter as outlined on the label.

"Anthem Flex herbicide, with two modes of action (Group 14 and 15), is proving consistent control of herbicide-resistant ryegrass and emerged broadleaves when farmers stay proactive with scouting and application timing," Rustom says. "This residual control is critical to reducing ryegrass since our postemergence control options are fading."

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FOR MORE INFORMATION:

-- Visit https://ag.fmc.com/…

-- Watch winter wheat time lapse video: https://youtu.be/…

-- View Italian ryegrass ID Tips: https://extension.okstate.edu/…

Always read and follow all label directions, precautions and restrictions for use. Some products may not be registered for sale or use in all states. FMC, the FMC logo and Anthem are trademarks of FMC Corporation or an affiliate. (C)2023 FMC Corporation. All rights reserved. 23-FMC-0603 02/23

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