Cheatgrass control provides challenge that producers must conquer to increase productivity
Cheatgrass, also known as downy brome, military grass or downy chess, not only reduces forage quality but can be a serious fire hazard, according to Steve Young, weed ecologist at the University of Nebraska.
Cheatgrass is native to southwestern Asia and was transported to North America through contaminated crop seed and ship ballasts. It was first reported in British Columbia in 1890.
Although cheatgrass is an annual weed that grows from seed, flowers, sets seed and dies each year, it can also produce a heavy infestation of seed in excess of 80 million seeds per acre. Once an infestation starts, it can be hard to get rid of, Young said.
“That is why it is important to control small patches before they spread,” he said.
Cheatgrass plants can grow six to 24 inches tall, depending on soil moisture. At emergence, the first leaves will appear brownish-green, but by maturity, they change to a purplish-tan.
Young said the leaf blades and sheaths are hairy, and the prominent ligule will have a membrane with a frayed margin. There are no auricles clasping the leaves to the stem. The plant has fibrous, relatively shallow roots and stems that protrude from a much-branched base.
“Cheatgrass is considered a winter annual because it usually germinates in the fall and grows rapidly until cold temperatures arrive,” Young said. “It may continue to grow through the winter, especially its root system.”
“It can also germinate in the spring, depending upon weather conditions. In the early spring, cheatgrass seedlings resume growth, produce seeds and die sometime between mid-July and early-August,” he explained.
Unfortunately, because of its early growing season, it has a competitive advantage over native, later-emerging or slower-growing plant species.
“It depletes the soil water reserves,” Young said.
As precipitation declines and temperatures rise, the plant has already taken in what moisture it needs to grow. This limits perennial grass seedlings from accessing that moisture so they can grow.
“A perennial grass will be challenged by competing with cheatgrass,” Young added.
Cheatgrass is also a fire hazard.
“It creates larger and more frequent fires because it increases fine-textured fuel,” he said. “Once cheatgrass is established, it is very persistent.”
Young doesn’t recommend using prescribed fire to control cheatgrass.
“Most often, it will just increase the cheatgrass population,” he said. “Cheatgrass seeds come through fire really well.”
Young said cheatgrass can be controlled by breaking the seed cycle, which means limiting the seed bank viability for at least two years.
It is also important to prevent seed production in the spring by maintaining the vigor of desirable species, like perennial grasses, through prescribed grazing, irrigation and adding nutrients to pasture grasses.
“We recommend that producers incorporate mechanical and chemical control methods,” Young stated.
A disk should be used to germinate and bury the seed, followed up by another disking or application of a chemical.
Glyphosate, more commonly known as Roundup, can be applied when dominant vegetation is dormant. Imazapic, or Plateau, can be applied in late summer or fall for pre-emergence to early post-emergence control.
The weed ecologist recommends using a combination of the two, known as Journey, and to apply the chemical before or right after emergence in late summer or fall.
Then, he advocates that producers reseed the area in the fall with a combination of desirable perennial species prior to chemical application.
Grazing and cutting
Producers can also help control cheatgrass populations through prescribed grazing if they have localized areas.
“It puts cheatgrass at a disadvantage and gives a chance for a more robust and resilient grassland system,” he explained. “The best time to graze is before the plants turn purplish-red and are producing seed.”
Producers can also mow localized areas, but Young said they will need to do it two times each spring to keep the cheatgrass from producing seed. He also recommended mowing low to the ground but cautions producers to do this no more than two years because it could damage perennial vegetation.
In pasture and Conservation Reserve Program land, Young emphasized the importance of groundcover to prevent cheatgrass from getting started.
“Plant a cover crop to control the cheatgrass,” he said. “By integrating seeding and chemical application, it will streamline the re-vegetation process, but check to make sure that species can withstand the herbicide.”
Young mentioned that studies are being conducted to develop bio-control agents for cheatgrass.
“There is a potential for what we call black fingers of death for cheatgrass, but it is still being tested and is not presently available for commercial use,” he explained.