Once hailed as a green guardian of soil health, annual ryegrass has now gone rogue in New York State. A cover crop champion turned chemical-defying challenger, this fast-growing plant has morphed into a resistant renegade, surviving glyphosate sprays and turning heads in the worst way.
Research titled “Glyphosate-Resistant Annual Ryegrass in New York State: The Case of a Cover Crop Becoming a Problematic Weed” from Cornell University has spotlighted this escalating issue. The research team, composed of Vipan Kumar and Antonio DiTommaso of Cornell’s School of Integrative Plant Science, along with Mike Stanyard from Cornell Cooperative Extension, paints a picture that’s both familiar and alarming for farmers in the Empire State.
Annual ryegrass, Lolium perenne L. spp. multiflorum, known to many as Italian rye, has long been a staple winter cover crop, prized for its quick establishment and vigorous growth. Brought to the U.S. from Europe during colonial times, it now blankets millions of acres across the country, fortifying soil structure and suppressing erosion.
But this green knight has a dark side. Left unmanaged, it grows up to four feet tall, outcompeting crops and seeding aggressively. The research notes its history of notoriety in other regions: “Annual ryegrass has been established as one of the most problematic weeds in small grain cereals, row and vegetable crops as well as along roadsides in the United States.”
It’s been ranked the most troublesome and difficult to control weed in winter cereal grains by the Weed Science Society of America. Now, it’s officially joined the ranks of herbicide-resistant weeds in New York.
For decades, glyphosate has been the go-to for terminating cover crops before planting. But starting in 2023, three farmers in Livingston, Ontario and Genesee counties discovered the hard way that glyphosate alone wasn’t doing the job anymore.
Despite applying multiple rounds of the herbicide at standard field-use rates, the ryegrass rebounded with gusto. Not only did it survive, it matured, headed out, pollinated and produced viable seed, turning treated fields into seedbanks for a tougher generation.
This wasn’t just a fluke or a weather issue. Greenhouse experiments conducted at Cornell’s Guterman Bioclimatic Laboratory confirmed it. New York now has a population of glyphosate-resistant annual ryegrass.
To verify resistance, researchers compared the New York strain with a known glyphosate-susceptible population from Arkansas. They applied nine escalating doses of glyphosate (Durango® brand) to both strains under greenhouse conditions. The results were dramatic.
The Arkansas plants succumbed to field-use levels. The New York ryegrass survived not only the standard dose but even the highest dose tested, which was a whopping 16 times the standard strength.
The research states bluntly, “Durango applied at the field-use rate … did not provide any control of the annual ryegrass population from Livingston County.”
Worse, even the strongest dose, 432 fl. oz./acre, failed to wipe it out. In technical terms, the resistant population showed a 22-fold resistance compared to the Arkansas strain.
Perennial ryegrass may be becoming a problem. Photo courtesy of Barry Rice, sarracenia.com, Bugwood.org
This isn’t just resistance. It’s resilience on steroids.
In the face of glyphosate failure, the research team pivoted to post-emergence herbicides in a 2025 on-farm trial. They tested a chemical cocktail of nine different combinations, including Select Max® (clethodim), Assure® II (quizalofop), Liberty® 280 SL (glufosinate), Gramoxone® SL 3.0 (paraquat) and mixes with metribuzin, plus combinations with glyphosate.
The experiment’s results speak volumes.
Gramoxone, alone, or with metribuzin and Liberty, or in combination with Select Max or Assure II, delivered 92% – 100% control at 21 days after treatment. Meanwhile, clethodim and quizalofop alone flopped, with control rates stuck between 10% and 25%.
In short, some chemical options remain effective, but only if chosen wisely and timed correctly.
The emergence of glyphosate-resistant ryegrass in New York raises alarm bells beyond the state’s borders. Once a problem primarily plaguing the South and West, herbicide resistance is now a Northeastern reality. The researchers noted findings “confirm the first case of glyphosate resistance in annual ryegrass in New York State.”
But this isn’t just about chemical failure. It’s about ecological and economic fallout.
Viable seeds from resistant plants can build up rapidly in the soil. Seedbanks become ticking time bombs, sprouting new resistance in subsequent seasons. Control costs skyrocket, requiring new chemistries, labor and equipment changes.
The Cornell team is rolling out a multi-pronged research initiative focused on mapping the spread of resistant populations across New York and the Northeast, investigating multi-herbicide resistance and how it evolves, exploring integrated weed management strategies and evaluating cost-effective methods to reduce the ryegrass seedbank in fields.
This means collaborating with growers, universities and Extension agents to craft a regional action plan because one resistant plant quickly becomes many.
What began as a helpful cover crop has become a stubborn saboteur of Empire State agriculture. Glyphosate-resistant annual ryegrass is already forcing farmers and scientists alike to rethink their strategies, revamp their sprays and reevaluate their fields.
As Kumar, DiTommaso and Stanyard warn in their research, alternative post-herbicide burndown chemistries can be used to terminate glyphosate-resistant annual ryegrass, but without long-term, integrated approaches, the problem will only grow – literally.
The grass may look greener, but it’s smarter, stronger and scarier than ever. Farmers, take note: Your next weed war might just be waged on your former friend.
by Enrico Villamaino
Leave A Comment