Soil bacteria may be answer to cheatgrass battle on Reach

Tri-City HeraldApril 16, 2013 

A naturally occurring soil bacteria could give native bunch grasses at the Hanford Reach National Monument the competitive advantage they need to edge out cheatgrass.

The invasive cheatgrass is the scourge of the monument, carpeting the ground like a lawn and providing the continuous fuel that allows wildfire to spread quickly. Native grasses, in contrast, dot the ground in clumps.

"Now we're seeing fires that are bigger and are burning more acres," said Michael Gregg, a land management research and demonstration biologist at the Mid-Columbia River Refuges Complex.

The wildfires kill the sagebrush and convert the historic shrub steppe land to annual grass lands composed mostly of cheatgrass, he said. It's a cycle that leads to more frequent, quickly spreading wildfires.

But field trials on the Saddle Mountain area of the Hanford Reach National Monument and elsewhere in the state, spraying with a carefully selected strain of the Pseudomonas fluorescens, has caused cheatgrass almost to disappear.

It doesn't happen quickly, said Ann Kennedy, a soil microbiologist with the U.S. Department of Agriculture's Agricultural Research Service at Washington State University Pullman.

Over three years in test plots up to 10 acres, about half of the cheatgrass disappears.

"But by five or six years, it is reduced to the point it really is not a problem anymore," she said.

It was the occasional yellow patches she would see marring the lush green fields of wheat in early spring in Eastern Washington that piqued her curiosity.

Soil testing showed a correlation between the stunted plants and a strain of Pseudomonas fluorescens bacteria. But the bacteria didn't seem to inhibit the growth of similar plants, such as barley.

"I wondered if we could go in the fields and find the same kind of bacteria that instead of inhibiting wheat would inhibit weeds -- cheatgrass and other annual grass weeds," Kennedy said.

She collected soils until she found Pseudomonas fluoresces bacteria strains that met her criteria and then further narrowed her choices to pick a strain that not only would not harm the plants she was trying to encourage, but would not harm microbes in the soil.

It's a biopesticide, which is more cost-effective than an herbicide and less damaging to the environment and human health, said Hilda Diaz-Soltero, Department of Agriculture senior invasive species coordinator.

In tests, including at the Saddle Mountain National Wildlife Refuge on the monument, the bacteria are sprayed on the soil in the fall right before it rains to drive them into the ground.

They grow and spread in the soil through the cold weather, ready to attach to the roots of the cheatgrass and produce a suppressive compound as roots begin to grow in the spring.

The bacteria do not kill the cheatgrass, just keep the roots from growing well, limiting the growth of the grass.

Normally, cheatgrass can out-compete native grasses. It germinates in the fall and grows at lower temperatures, using its head start on native grasses to grow root masses that take up more than their share of space and water.

It chokes out the native bunch grasses that don't have enough water in May and June to grow seeds and instead die off, Kennedy said.

Environmental Protection Agency regulations have limited tests with the bacteria to plots smaller than 10 acres until the strain of Pseudomonas fluorescens Kennedy identified is federally registered as a bioagent.

With cheatgrass spreading at the rate of thousands of acres per day in the Great Basin states of Nevada, Utah, Oregon and California, the U.S. Fish and Wildlife Service has committed $200,000 to move the USDA research toward practical use. The money will be used to scale up tests to meet EPA biopesticide registration requirements.

The tests are needed to see how the bacteria performs on a large scale and also to understand the best delivery method to give the bacteria the highest chance of surviving the winter and being ready to colonize cheatgrass roots in the spring, Gregg said.

Licensing the bacteria could be five or more years off, Diaz-Soltero said.

But Gregg is convinced that Pseudomonas fluorescens is worth the effort.

"To go back to the natural state, we need to break the fire cycle," he said. "Cheatgrass is the driver that increases wildfires in the West."

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