Putting Invasive Weeds in the Crosshairs
Cheatgrass. (Photo by Jaepil Cho)
The western portion of the country, 11 states, is responsible for nearly 25% of the nation’s agricultural wealth, but it could be much more. Scientists with the Agricultural Research Service (ARS) are trying to make that happen.
Those states – Washington, Montana, Wyoming, Oregon, California, Nevada, Idaho, Utah, Colorado, Arizona, and New Mexico – collectively account for more than $118 billion of America’s agricultural business. They are also home to numerous non-native, invasive weeds that choke off billions of dollars in potential revenue and expenses due to lost crop cultivation, livestock forage, recreational use, mitigation treatments, and more.
Cheatgrass and Cape-ivy are among the weeds that are targets of a 5-year project led by Patrick Moran, an entomologist with the ARS Invasive Species and Pollinator Health Research Unit (ISPH) in Albany, CA. Moran’s team is discovering, identifying and characterizing new biological control agents – most often, insects and mites from the weeds’ native ranges that target the invasive plants, but also plant microbes already in the U.S.
Biological control agents are safe, natural predators of targeted pests that can join the integrated weed management toolkit. Integrated weed management uses several control techniques in a well-planned, coordinated, and organized program to reduce the impacts of weeds.
“Cheatgrass is often described as the most successful invasive plant in North America,” said Brian Rector, an entomologist who co-leads the team. “Current estimates suggest the weed occupies over 210,000 square kilometers (about 130,500 square miles) in the semi-arid shrublands of the region.”
Cheatgrass fuels wildfires that destroy native grasslands and degrade rangelands used by livestock. Applying chemical treatments to control cheatgrass costs about $15 per acre, but the search is on for biological control agents, Rector said. Biological control research on cheatgrass has led to the discovery of flies and weevils in eastern Europe and the Mediterranean that feed on seeds or stems. Researchers have also made advances with microbes already present in the western U.S. that slow plant growth or kill seeds.
“Evidence suggests that weed-suppressive microbes such as fungi occur in soils that harbor invasive grasses,” said Rebecca Mueller, a microbiologist on the team. “The discovery of new bacteria (or strains) that are adapted to a broader range of environmental conditions may also greatly enhance integrated weed management of cheatgrass.”
Cape-ivy. (Photo by Scott Portman, ARS)
In California, Cape-ivy, sometimes derisively known as the “kudzu of the West,” is one of the state’s worst invasive plants. Like kudzu, Cape-ivy grows over native shrubs and trees to form a solid layer that blocks out light and smothers other vegetation. It can also clog streambanks in coastal agricultural areas. According to Moran, federal and California agencies spend hundreds of thousands of dollars and thousands of hours per year to control Cape-ivy.
In response, Moran’s team, including now-retired ARS entomologist Joe Balciunas and collaborators in South Africa, found and investigated an insect that can be used as a biological control agent to combat Cape-ivy: the Parafreutreta regalisfly. P. regalis lays its eggs inside the stems of cape-ivy, which then form galls on the plants. Galls reduce the size and speed of growth. Careful lab testing before release demonstrated that the fly poses no danger to native plants or crops. Moran’s team received a permit from USDA and released the fly in 2016; it is now established at 12 sites along the California coast.
While initial results are promising – Cape-ivy vine cover has declined by 15-30% at the first two sites where the galling fly was established – Moran said that impact studies are ongoing and will continue. It takes 5 to 10 years after release to evaluate the success of a biological weed control program.
Classical biological control of invasive weeds is a safe and cost-effective method to manage invasive alien weeds in non-crop areas, Moran said, noting that the benefit-to-cost ratio ranges from 8:1 to 300:1 worldwide.
“It’s important that we develop new tools for invasive weed and pest insect management in the Western U.S. that are economically and environmentally sustainable and have promise for solving other intractable threats to water and soil resources for agriculture and native plant and animal species,” Moran said. – by Scott Elliott, ARS Office of Communications