Beating a cheat

Jan 18, 2015 By Eric Blom, Staff Writer

County group to try an experimental, biological agent to suppress cheatgrass

Cheatgrass pops up in just about every environmental, land management or natural resource issue in the West because it out-competes native grasses. The flora affects water flows, stops ecological procession and supplies poor forage.

Its worst characteristic, however, is that it makes wildfires worse.

Killing cheatgrass is tricky, but a group in Fremont County is trying an experimental method that could suppress the weed without much trouble.

"If the bacteria works, you can just put it out there ... you can basically apply it and sit back and let it do its work over the next few years," Fremont County Weed and Pest supervisor Aaron Foster said.

Foster is helping with the project, but the Popo Agie Weed Management Association is leading it.

The bacteria involved is Pseudomonas fluorescens strain ACK55. It attacks the roots of cheatgrass and two other invasive grasses, but the bacteria leaves native grasses alone, according to research at the U.S. Department of Agriculture Research Service at Washington State University.

When its roots cannot grow well, the plant cannot produce as many seeds, and cheatgrass cannot grow back as strong each year.

"If you can remove the seed bank and a seed source, you can slowly move cheatgrass out," Foster said. "With time you can give the natives a chance to re-establish."

Foster hopes the microbial method will be a "game changer," but he is waiting to see how it works. Just because it works in Washington does not mean it will work in Fremont County.

"It's just a matter of will it work in our climate and our soils," Foster said.

Testing a theory

To test if it will, the Popo Agie Weed Management Association plans to take roughly 10 grams of the freeze-dried bacteria, called PF strain, thaw it out, mix it with 10 gallons of water and disperse it from a helicopter over five acres around the Rise of the Popo Agie in Sinks Canyon.

Converse County Weed and Pest has been working with USDA Research Service and provided the Weed Management Association with the PF strain.

Foster hopes to apply the bacteria in the spring, but weather conditions would determine the exact date.

Several years of observation will be necessary to know if the PF strain works.

"It takes a couple years for it to get to the levels in the soil where it will have a noticeable impact on the invasive species," Foster said.

Additionally, cheatgrass seeds can fall to the ground and remain viable for five to seven years, so for several years new cheatgrass could grow from seeds produced before the PF strain was introduced. The affect the bacteria has on the number of seeds produced would take about that long to show up.

Even if the experiment is successful, Foster thinks the bacteria would have to be applied again after several years for it to continue to work, because over time the abundance of the microbe would diminish. Still, the procedure is an easier control method than the herbicides used now.

The window to apply the chemicals is short, right around when cheatgrass germinates in the fall, and applicators must be precise, because too much of the chemical can hurt native grasses in addition to the cheatgrass, Foster said. The PF strain's timeframe is wider. The ground should be free of snow and temperatures between freezing and 50 degrees.


Foster likes that the bacteria is a native, biological control agent. The bacteria came from soil in the northwest United States., and researchers isolated the PF strain from other microbes, because it attacked invasive grasses in particular.

"It will be, in essence, a bio-control for cheatgrass where the control agent is naturally occurring in North America and the western U.S.," Foster said.

Cheatgrass likely made its way to Fremont County from the Great Basin area by grain shipments and livestock carrying its seeds, Foster said. It was first recorded in local areas in the early 1900s.

The invasive species is thought to be native to Central Europe and the Mediterranean region. It has been found in every state of the United States and covers millions of acres, primarily in the West.

Wildfire danger

It expands quickly in areas disturbed by wildfires or development, such as mining and oil and gas drilling.

A major concern with the species is that it dries earlier in the year than native grasses and grows thicker, a perfect recipe for strong wildfires. Infected areas in turn burn more frequently, and cheatgrass can re-establish itself quicker than other plants, Foster said, continuing the cycle and effectively halting the natural ecological transition from grasses to shrubs to trees and back to grasses after a fire.

Cheatgrass is only good forage for wildlife and livestock for the month it remains green, Foster said.. Native grasses are better in that regard, because they do not dry out until later in the year. Small, pointy structures called awns on cheatgrass seeds also can irritate animals that eat it.

Infestations of cheatgrass also can have an impact on water flows.

"How the ecosystem functions can be affected by it," Foster said.

Bushy sagebrush holds snow well throughout Wyoming's windy winters, but cheatgrass does not. The snow blows off much easier. Then when springs comes and melts the snow, areas covered in sagebrush receive much more moisture than cheatgrass-covered ground.

If it works, PF strain could be a powerful tool to fight cheatgrass.

"If it does work, you could apply it over a large scale and have a pretty good increase in our desirables," Foster said, referring to desirable, native grasses.

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