Mites enlisted to battle weeds
- By Katie Klingsporn WyoFile.com
- Oct 6, 2022
- 0
The noxious invasive weed whitetop, which has colonized vast tracts of the West, has long confounded landowners and resource managers. Also known as hoary cress, the plant proliferates quickly, has no natural North American predators and is reportedly toxic to cattle in large quantities.
An unlikely warrior has emerged in the whitetop battle: a microscopic mite from Europe that researchers believe can stunt the weed’s growth. This summer, land managers released the mite in Wyoming for the first time.
“We’re really excited about having the mites,” said Dr. Tim Collier, a University of Wyoming associate professor who specializes in biological control of rangeland weeds. “Whitetop is a huge problem in Wyoming.”
Technicians spread mite-infested “galls” — plant deformities caused by feeding mites — on a 3.5-acre piece of state-owned property in Fremont County in May. The hope is that the mites in the galls will spread to live plants and create new galls, which impede growth.
Dr. Jeffrey Littlefield, a research scientist at Montana State University in Bozeman, is a major player in the whitetop mite effort, a collaboration many years in the making that spans the globe.
The plant-stunting gall mite in question, Aceria drabae, hails from northern Greece.
“It’s been known for a number of years and was thought to be a potential bio control agent for whitetop,” Littlefield said.
A biological-control laboratory began transporting the tiny creature to a containment facility at MSU in the mid-’90s, Littlefield said. Over the years of transfer, testing and monitoring, researchers found positive results. The mites produce different galls that prevent the plants from going to seed, Littlefield said. Galls also spread to secondary stems and forced their host plants to divert energy that would otherwise be used to proliferate.
“They can really stunt the plant,” he said.
Littlefield and his team had to secure U.S. Department of Agriculture regulatory approval. The process for approving biological control agents — natural enemies such as parasites, predators or pathogens — is painstaking and comprehensive.
“And that took probably another good six years or so,” Littlefield said.
But that approval gave Littlefield and his collaborators the green light to release the mites on wild whitetop plants, which they first did in Montana in 2019.
The first year they put mites in one Montana site, Littlefield said, they counted 10 gall-infected stems.
“This past year we’ve had well over 6,000 stems,” he said. “We’re finding not only the number of infested stems has increased, but the gall intensity has increased.”
The hope is to slowly grow the program in order to facilitate releases in more of the West and see a slowing or reversal in the weed’s colonizing patterns.
When the mites became available for release, the Wyoming Weed and Pest Control Council wanted in on it. Whitetop has, after all, affected every county in the state, Larry Smith, president of the Wyoming Weed and Pest Council, said in a release.
There are plenty of introduced plants that don’t cause ecological disorder, said Fremont County Weed and Pest District Supervisor Aaron Foster, who chairs the Wyoming Biological Control Steering Committee.
“But some have the advantage of being competitive and can cause havoc,” he said. “And whitetop is one of those.”
Whitetop “has the ability to use that root system to crowd out the surrounding vegetation,” Foster said. “And it grows and it forms these dense monoculture patches. And they just get bigger and bigger and kind of expand, and start pushing out the desirable grasses, the other forbs that are in there that we like, and pretty quick, the dominant plant is whitetop.”
That’s not good for biodiversity, wildlife or agriculture, he said.
The site near Dubois was selected for a few reasons, Foster said. Fremont County has been a longtime and significant contributor to biological control, research and development in Wyoming, he said, and county weed and pest officials already had sites identified and prepared there.
Now that the mites have been released, the next step is to wait, monitor their effect and evaluate whether to distribute them more widely, Foster said.
The project will take years and isn’t expected to eradicate whitetop in Wyoming. But the hope is that it can slow the spread and save money by preventing other, more expensive measures.
Global Plant Protection News 
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