Weed & Pest
Research continues, exploring cheatgrass biology and control mechanismsWritten by Natasha Wheeler
“Typically, we think about cheatgrass as a winter annual. It germinates in the fall if it gets sufficient moisture and extends its roots during the winter when most of our perennial grasses are dormant,” explains Brian Mealor, Sheridan Research and Extension Center director.
In the spring, cheatgrass is prepared to take up moisture before other grasses can, giving it a competitive edge.
“The biggest problem with cheatgrass, besides that fact it doesn’t produce a whole lot of forage in dry years, is that it dries out early. It can take on fire in a whole different scale than a lot of our perennial grasses do,” Mealor adds.
Cheatgrass begins to turn purple as early as mid-May, and it is ready to burn shortly thereafter. Other species, such as sagebrush, are not able to persist after frequent fires.
“Sagebrush can’t regrow from the root crown. It has to come back and reseed. When we think about cheatgrass and what it can do to change how a sagebrush ecosystem works, it becomes an even greater issue than it does only from a grazing standpoint,” he says.
From a grazing standpoint, cheatgrass experiences large variability from year to year. It can go from producing several tons of forage per acre in wet years to almost none in dry years.
“If we have a lot of cheatgrass in our operation, an effective grazing plan from year to year becomes more difficult, especially when we have those fire issues,” Mealor notes.
Because cheatgrass is an annual plant, pulling it up from the root will kill it.
“But when there are millions of these plants across a meaningful scale, it can be kind of an issue,” he comments.
Also, because cheatgrass reproduces from seed each year instead of persisting through the seasons, control mechanisms can be limited when managing the weed.
Currently, scientists and producers are grappling with management techniques for the weed by experimenting with herbicides, grazing and bio-control mechanisms.
“Cheatgrass is easy to kill but hard to remove from the system,” Mealor states.
Synthetic herbicides are typically the most common control mechanism used for cheatgrass, and different varieties are typically applied before the weed emerges in the fall.
“We’ve done research over the past six years looking at different herbicides or herbicide mixes for controlling cheatgrass. We were successful with almost all of those, getting anywhere from 85 to 100 percent cheatgrass control without too much damage to the other grasses. But, after two, three or sometimes four years, the cheatgrass starts to come back. That goes back to that seed production,” explains Mealor.
Each year, plants produce seeds that drop into the soil, and approximately 90 percent of any given year’s seed crop will germinate within the following year. The remaining 10 percent can carryover for as long as nine or 10 years.
“The sheer quantity of seed we may be working with makes it a numbers game. Even if we get 90 percent of the seed that germinates in one year and we can kill it, we still have the potential of carrying over tens, if not hundreds, of pounds of seed per acre after that,” Mealor adds.
In the short term, synthetic herbicides are relatively affordable and effective, and they are also relatively easy to apply over large areas of land.
“One con, in addition to relatively short-lived control, is sometimes we see an increase in potential non-target damages,” he says.
There are also regulatory issues that may limit or prevent the application of certain herbicides.
Scientists have also explored using grazing to control cheatgrass with limited success.
“The biggest challenge besides keeping a high enough stocking density is, if we’re working in some bigger pastures, being able to reduce grazing pressure at a time when we are not harming those other cool season perennials that we want to keep,” Mealor notes.
Although livestock will eat cheatgrass and grazing can be considered a “green” control mechanism, it is not overly effective.
“This might be something we could work into a system, maybe doing some seeding in conjunction with grazing, but it’s probably not going to be the best approach because we don’t yet know how to do it effectively,” he remarks.
Using soil fungus, such as the product known as Black Fingers of Death, is also a method that scientists have been exploring, but results are slow to materialize.
“At best, it’s only going to attack 10 percent of the current year’s seed crop,” Mealor notes.
The fungus attacks the seed before germination, killing the embryo and preventing the seed from germinating. Scientists are still researching other plants affected by the fungus.
Another potential cheatgrass management tool is weed-suppressant bacteria, although there are still many unanswered questions about the impacts of its use.
“The claims are we can see up to 100 percent cheatgrass suppression after about six years of application,” he comments. “We may not even know we did something for the first three or four years. After three years, claims are that we’ll see 50 percent reduction in cheatgrass and then 90 percent-plus after that.”
Although he is waiting to learn more from ongoing studies, Mealor says, “Before I jump on the bacteria bandwagon, I would like to see some more positive results.”
With current research, Mealor notes that the most effective control may be using a systems approach.
Brian Mealor spoke at the Progressive Rancher Forum in Casper on Nov. 30.