Uncontrolled ryegrass is notorious for competing with crops, which can reduce yields for producers. LSU AgCenter weed specialists Donnie Miller and Daniel O. Stephenson are focused on curtailing the spread of ryegrass in crops and, as with most things in life, timing is everything.

Miller, who works out of the Northeast Research Station in St. Joseph, said that ryegrass continues to be a troublesome winter species to all crops.

Miller said if growers can’t control the grass, it becomes a tremendous competitor with crops, especially those planted early, such as corn, which reduces yield for producers. The weed may also host insect populations, which is doubly problematic. Often attention is not focused on later-emerging spring populations or earlier misses in control until it’s too late, Miller said. And the size of the ryegrass limits effective control in populations that aren’t resistant to over-the-top herbicides.

For his part, Stephenson agreed that glyphosate-resistant ryegrass has become a major problem. He and Miller are in the third year of a project looking at different techniques to control ryegrass.

Initiated in fall of 2022, their research in ryegrass management expanded in fall of 2023. Thus far, findings show that the use of cover crops and/or herbicides applied in the fall after harvest can be effective tools in combatting spread.

“Initial indications are that cereal rye can effectively compete with emerging ryegrass and limit tiller and seedhead production,” Miller said. “The ryegrass tiller number in spring of 2024 was reduced 43% with only cereal rye planted in fall at an 80 pounds per acre seeding rate and reduced 50% with only s-metolachlor applied in the fall at 1.33 pints. The combination of the two, however, resulted in a 95% reduction by spring of 2024.”

Seedhead production, however, was only significantly reduced by the combination (93%), according to Miller.

A second part of this approach is identifying optimum timing for herbicide application in relation to cover crop and ryegrass emergence, Miller said.

“Unfortunately, these species often emerge simultaneously,” he said. “So having the herbicide out as early as possible is most beneficial.”

Research initiated in the fall of 2023 has shown that some residual herbicides, such as s-metolachlor or pyroxasulfone, can be applied at the spiking stage (80% emerged cereal rye or black oats), while others such as metribuzin and clomazone are much better tolerated when applied two weeks after emergence to one- to two-leaf plants.

“When coupled with Dual Magnum, a soil residual herbicide applied two weeks after cover crop emergence in fall, producers have an effective program for managing ryegrass during winter and spring months ahead of planting,” Miller said. “In addition to weed management, agronomic and soil benefits associated with cover crops are realized.”

Miller went on to say that this combination offers a one-two punch approach to ryegrass management, allowing the soil herbicide to eliminate or limit emergence of ryegrass during late fall and early winter months while the cover crops limit spring emergence and competition due to prolific biomass production in spring.