In the South, ryegrass quickly turns from winter grazing savior to competitive Satan for warm-season grasses. That time is quickly approaching, and advanced control planning is in order to get those warm-season perennials off to a fast and productive start.
Unfortunately, complicating the ryegrass control issue is building herbicide resistance within this cool-season grass species.
“Late-season annual ryegrass can delay or prevent the growth of warm-season perennial forages such as bermudagrass or bahiagrass,” says Vanessa Corriher-Olson, Texas A&M AgriLife Extension forage specialist.
In warm-season grass hayfields during early spring, ryegrass seeds deposited in past years germinate and can grow prolifically in a very short period of time. In pastures that were seeded to ryegrass last fall, it’s the rapid spring growth of established plants that are cause for concern.
“Making an herbicide application is probably the most common control alternative,” Corriher-Olson says. “Timing is critical along with following label directions.” There are several alternatives.
Prowl H2O (pendimethalin) can be used in dormant bermudagrass or bahiagrass monoculture hayfields and pastures prior to ryegrass emergence. Ideally, time these applications prior to a rainfall for enhanced soil incorporation.
The most effective control of emerged ryegrass in bermudagrass is accomplished in the fall or early winter using Pastora (nicosulfuron + metsulfuron). Plants need to be less than 6 inches for best results. Pastora cannot be used in bahiagrass fields; it also should not be used in fields where summer annual forage plantings are planned.
During late winter (February), Patrick McCullough recommends that Pastora treatments be tank-mixed with glyphosate to enhance control. The Georgia weed management specialist notes that moderate rates of glyphosate generally do not affect the spring transition if applied in winter. That may not be the case if applied during spring.
There are not any selective postemergence ryegrass control options in bahiagrass or tall fescue.
Herbicide resistance is complicating postemergence control of annual ryegrass in bermudagrass. In Georgia, McCullough notes that he has documented resistance to both Pastora and glyphosate. Resistance develops from the repeated use of the same herbicide or mode of action over a period of years.
In many cases, cultural control measures will help to reduce or eliminate the need for chemical control. Corriher-Olson emphasizes the importance of plant competition from the warm-season grass. “Maintain a stubble height of 4 inches or more,” she says. “This helps to provide shade, inhibiting ryegrass germination.”
For pasture situations, graze pastures such that the ryegrass is kept short and not allowed to go to seed. If livestock can’t keep up with the ryegrass growth, those paddocks may need to be sprayed with an herbicide or cut for stored forage.