AgKnowledge: Number 63: UI Scientists Want to Take a Bite Out of Hawkweed

UI Scientists Want to Take a Bite Out of Hawkweed

hen University of Idaho biocontrol expert Joe McCaffrey takes visitors to his hawk- weed research site in a Benewah County pasture, he asks them to look straight down. At their feet they behold an impenetrable mat of hairy, ground-hugging leaves from as many as 3,200 hawkweed plants per square yard. “They’re literally on top of each other,” says McCaffrey.
“It’s virtually taking over every place it can get to, and it’s becoming more dense in the places it already exists,” says Ben Marsh, former Benewah County weed supervisor and president

Corinne Flowers, left, and Cindy Jette, both UI research assistants, count hawkweed plants in a plot near Fernwood.

of the St. Maries-based Hawkweed Action Committee, a grassroots group representing businesses, government agencies, and citizens determined to fight the weed.
     At elevations from 2,100 to 5,400 feet in Idaho, Montana, western Washington, and southern Canada, meadow hawkweed—a European import—is overrunning pastures, forest clearings, roadsides, mountain meadows, and even lawns, painting them a vivid yellow in June.
     Cultivation and herbicides keep the weed out of cropland, but only costly herbicides or dense shade discourage it elsewhere. “What do you do when it’s gotten into those upper, pristine meadows?” asks Marsh. “That’s why our focus is on biocontrol.”
     With action committee funding, McCaffrey has been studying hawkweed as a candidate for biocontrol. This year, that research helped him and graduate student Linda Wilson to secure a major grant from the U.S. Department of Agriculture to study the feasibility of biocontrol.
     Biocontrol pits the weed against hostile insects or other creatures—usually natural enemies collected from the weed’s home turf. But releasing European insects to control meadow hawkweed here is complicated by the presence of native hawkweeds.
     “If we want to bring agents in to control the weedy ones, they had better not be a pest of the native ones,” says McCaffrey.
Luckily, Wilson and McCaffrey discovered meadow hawkweed has one part the natives don’t: runners, or stolons. “If we target that organ for attack,” says McCaffrey, “we don’t have to worry about the natives.”
     McCaffrey and Wilson have two to three years to gauge whether European stolon-attacking insects might control hawkweed here. Wilson is also looking at whether fertilizer can help pasture grasses compete with hawkweed. UI weed scientist Donn Thill is evaluating herbicides. Eventually, biocontrol agents, fertilizer, herbicides, and competitive plants should all help combat the weed.
     “These pre-release studies have rarely been done in the past,” says McCaffrey. And yet they could save taxpayers many millions of dollars, the everyday price-tag for most biocontrol efforts, especially if the studies suggest stolon feeders won’t work.
     Locating and testing the insects is the job of the International Institute of Biological Control (IIBC) in Switzerland and the USDA Agricultural Research Service in France. The action committee has joined with New Zealand—where hawkweed has overrun sheep grazing lands—to share the costs of IIBC research.
     “Joe established the lines of communication [with IIBC],” says Marsh. “Their knowledge of him helped to open the door.”
     McCaffrey thinks five years is the soonest a biocontrol agent could be ready for release in Idaho.
     For more information, call (208) 885-6681.

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