Microbe management

Even during winter, the sagebrush slopes of much of the Great Basin are spotted with the golden-brown remains of last year’s crop of cheatgrass, an invasive species that helps spread wildfires in the West. Researchers from the Great Basin Institute in Reno are now investigating a means for controlling this fast-growing invader with a weed-suppressing bacteria called ACK55.

ACK55, a strain the Pseudomonas fluorescens bacteria, occurs naturally in the environment and is found in all soils, including those of the Great Basin. This particular strain was discovered and isolated from a soil sample taken near Pullman, Washington, by soil scientist Ann Kennedy of the U.S. Department of Agriculture. Kennedy’s initial tests showed exciting results – ACK55 produced a compound that reduced the root growth in certain species of invasive grasses, but didn’t harm the surrounding plant community.

“We searched through 25,000 isolates to find those that suppressed cheatgrass, medusahead, and jointed goatgrass, but did not inhibit crops or native plants,” said Kennedy. “In addition, the bacteria does not inhibit broadleaf plants.”

Now, a Reno-based research team is working with Kennedy to test the effect of ACK55 on controlling the spread of cheatgrass in the warm, dry soils of Nevada’s sagebrush habitats. Cheatgrass, a type of grass introduced from Eurasia during the late 1800s, is problematic for several reasons. It begins growing during winter, earlier than many of our native plants and grasses. By getting a head start, this invader is able to outcompete surrounding plants for water and nutrients. It grows quickly, produces large numbers of seeds, and finishes its life cycle by mid-June; the body of the plant then dries, leaving behind fuel that contributes to the spread of wildfires.

During September 2015, researchers from the Great Basin Institute in Reno began setting up experimental study plots to test the effectiveness of ACK55, working in collaboration with Kennedy, the U.S. Fish and Wildlife Service Partners Program, the Great Basin Landscape Conservation Cooperative and private landowners.

The team found property owners near Spanish Springs and in Humboldt County’s Eden Valley who were willing to give the bacteria a try on parcels of cheatgrass-infested rangeland. The bacteria are most active during times of year when temperatures are cool and grass root growth is most competitive—late fall and early spring.

In November, associates Zac Haley and Lyndsey Boyer worked from an ATV to spray an ACK55 solution across one-acre plots. The team will spend the next three years monitoring to see what happens, setting up photo points and collecting data on plant growth. What do they expect to find?

“It’s supposed to inhibit the root growth, which will then allow the native plants to achieve more water uptake and therefore outcompete the invasive grass,” Haley said. “It’d just be really good for taming cheatgrass in all kinds of fire-damaged areas.”

Until now, the only remedy for cheatgrass has been treatment by chemical herbicide—an unappealing prospect, considering how far and how fast the weed has spread across the West. The research team hopes that ACK55 will provide a more natural solution.