Arkansas Row Crops Radio · University of Arkansas System Division of Agriculture

Weeds AR Wild S3 Ep19. Italian ryegrass (9/20/2023)

·43 min·4 clips

A ryegrass biotype in North Carolina survived 1024 fluid ounces of paraquat, showing unprecedented herbicide resistance.

This episode focuses on the management of Italian ryegrass, a significant and resistant weed in Southern row crops. Host Tom Barber, an Extension Weed Scientist from the University of Arkansas, is joined by specialists Dr. Jason Bond from Mississippi State and Dr. Charlie Cahoon from North Carolina State. Charlie Cahoon details the evolution of resistant ryegrass in North Carolina, beginning with ALS and ACCase resistance, followed by glyphosate resistance roughly 15 years ago. He reports the 2020 confirmation of paraquat-resistant ryegrass, with one biotype surviving a 32X rate of the herbicide. Some populations now exhibit three- or four-way resistance to paraquat, glyphosate, ALS, and ACCase inhibitors. Jason Bond outlines Mississippi's history with ryegrass, including ALS resistance dating to the 1990s, widespread glyphosate resistance discovered around 2004-2005, and more recent cases of clethodim and pinoxaden resistance. The specialists discuss shifting emergence patterns, with Charlie noting research showing ryegrass seed tends to emerge in the same season (fall or spring) as its parent plant. Jason observes that while a major fall flush is typical, recent years seem to show increased spring emergence, potentially due to aggressive fall control measures. The conversation covers the critical yet complex timing of fall residual herbicide applications, balancing ideal weed control with harvest schedules, labor, and weather. For fall residuals, Jason Bond identifies metolachlor as a primary choice for its accessibility, price, and performance, often mixed with metribuzin for synergy with paraquat. He also notes the value of Command (clomazone) in rotations preceding rice. The group agrees products like Warrant, Prowl, and Treflan generally provide weaker or less consistent ryegrass control. Charlie Cahoon expresses concern about over-reliance on Group 15 herbicides like pyroxasulfone, fearing imminent resistance. A key insight is that ryegrass seed has a relatively short soil lifespan, estimated at 16-17 months, meaning aggressive control for two to three seasons can drastically reduce problem populations. The specialists stress that all post-emergence control options are imperfect, with control percentages dropping rapidly with any application error or unfavorable condition. Charlie emphasizes that in areas with paraquat resistance, a missed fall residual means there may be no effective post-emergence option at all. The tone is conversational and educational, featuring an informal exchange between colleagues who frequently use sports anecdotes and personal observations alongside research data. The style is highly practical, focused on providing actionable recommendations and strategies for farmers. This episode is ideal for row crop farmers, agronomists, and crop consultants in the Southern U.S. who are battling resistant Italian ryegrass. Listeners interested in cover crop integration and long-term resistance management will find valuable insights. Those seeking a broad, introductory overview of weed science or who farm in regions where Italian ryegrass is not a primary concern may find the specific details less applicable.

As heard by us

A practical guide to Italian ryegrass timing when harvest windows are tight.

Italian ryegrass is the pressure point, and the episode is most useful for its timing advice. Tom Barber and his guests take a messy fall management problem and make it workable: watch harvest progress, watch the forecast, and be ready to move when the field opens up.

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Why you'd press play

You need a timely ryegrass plan before harvest timing leaves you boxed in.

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