Ryegrass continues to spread across Delta

Glyphosate-resistant Italian ryegrass continues to spread across the Mississippi Delta. Almost two hundred people attended the glyphosate-resistant Italian ryegrass field day held at Mississippi State University’s Delta Research and Extension Center on Thurs., Mar. 10.

“The great crowd at the ryegrass field day shows that growers, consultants, extension agents, and industry reps in the area are keenly aware of how serious the problem is,” said Jason Bond, weed scientist and an organizer of the field day.

Speakers included researchers and weed scientists from MSU’s DREC, the U.S. Department of Agriculture-Agriculture Research Service, the University of Arkansas Division of Agriculture and North Carolina State University. They addressed the biology of ryegrass, its identification, fall and spring herbicide programs and the development of glyphosate-resistant ryegrass.

“Glyphosate-resistant Italian ryegrass is a serious problem for crop production in the Miss. and Ark. Delta regions. In monitoring the weed over the last several years, we have watched it increase from a few locations to most of the Delta,” Bond said. 

The weed was first identified in Mississippi’s southern Washington County in 2005 and since has been identified in 12 of the Delta’s 19 counties, as well as in Ark., La. and N.C. Resistant populations are also suspected in western Tenn.

Ryegrass is a common weed often used for roadside stabilization. It becomes a problem when it appears in crops. Resistant species can compromise traditional herbicide burndown approaches.

“Ryegrass is very aggressive and its seed may remain in the ground for years,” said Robin Bond, a research associate at DREC.

A single plant can produce 45,000 seeds, which can wreak havoc on a field in just a few years.

In addition to exhibiting resistance to glyphosate, Italian ryegrass has also shown resistance to other herbicides such as Hoelon®, Osprey® and Powerflex®. Researchers at DREC and USDA-ARS have been working together to learn more about managing the weed. Using molecular mapping, USDA-ARS biologists have developed a genetic sequence of the weed to help determine how better to combat it.

“Genetic sequencing has shown that ryegrass is a very diverse plant that has the ability to adapt to various treatments,” said Jeff Ray, USDA-ARS research geneticist.

The weed has been identified over most of the North American continent. Yet, the mild Mississippi Delta winters and fertile soils are ideal for Italian ryegrass. Researchers at the field day recommended fall and spring treatments as a good combination for combating the weed.

“I learned what we are going to have to do to help growers control glyphosate-resistant Italian ryegrass. Control efforts need to begin in the fall,” said Don Respess, MSU Extension Agent in Coahoma County.

Peak emergence for Italian ryegrass takes place in the fall but the weed overwinters to produce another large flush in the spring.

 Treating fields in the spring is as important as doing so in the fall,” said Jerry Singleton, MSU Area Agronomic Agent.

Researchers discussed the pros and cons of several herbicide treatments they had tested, and encouraged producers to get a handle on this aggressive weed.

“We can handle glyphosate-resistant Italian ryegrass in the Mississippi Delta if we use a multi-faceted approach with fall residuals and spring controls of clethodim and/or paraquat,” said Tom Eubank, DREC soybean scientist.