UI's weed specialists help train weed-identification team

by Bill Loftus

Hoary cress, a weed better known as whitetop (Lepidium draba ssp. draba), sprouts from a field last tilled perhaps 50 years ago in the Salmon River Breaks near White Bird.

A dozen weed control experts listen to University of Idaho weed scientist Tim Prather discuss strategies for delineating boundaries of the weed patch.

Prather has high-level backup in the exercise. Idaho County Weed Supervisor Carl Crabtree leans in to expand the discussion, as does Leonard Lake, who directs the Nez Perce National Forest’s invasive species program.

The county, federal, and university partnership in 2005 began developing a process to identify and control weed infestations early. Wiping out two small patches of leafy spurge (Euphorbia esula) along the Lochsa River cost only a few hundred dollars but prevented an infestation threatening thousands of acres, Prather said.

The partnership focuses on prioritizing search efforts to concentrate weed surveys on areas most likely to hold newly invading weeds. That strategy is a critical part of a strategic plan completed in January 2005 by the Idaho Invasive Species Council.

This steeply sloped field is where a rancher once grew dryland grasses for hay, to help get livestock through winter. In the years since, it has been used mostly to winter livestock and big game animals.

Sandra Robbins and Tim Prather examine
a member of the Artemesia or sage family
Photo by Mark LaMoreux

“Right now, it would be hard to find anything here that wasn’t a weed,” said Leon Slichter, one of the Idaho County weed control staff whose job is to track and control infestations.

Thistles sprout where whitetop is sparse. Greening grasses signal the presence of other invaders.

For the stockman, the field probably works all right, furnishing feed for his animals, Crabtree said. For the county, getting a handle on weeds and preventing their spread is a higher priority for the common good.

Helping the few against the many

It is a big job. Idaho County covers nearly 8,500 square miles or 5.5 million acres, more than the total land area of Massachusetts. Crabtree’s crew numbers fewer than a dozen.

Other workshop participants contemplate
other weeds.
Photo by Mark LaMoreux

That’s the point of Prather’s presence. He joined Sandra Robins, of the college’s Lambert Erickson Weed Diagnostic Laboratory, in the field with the Idaho County and U.S. Forest Service crew members to fine-tune a strategy.

Their goal is to give the few a fighting chance against a multitude of invasive species. Prather and Lake ask participants to fire up their hand-held computers equipped with global positioning system units. The 8-ounce computers lock into satellites overhead to fix their position on the ground.

Team members crisscross the field, marking the hoary cress boundaries. The procedure requires searchers to test their abilities to identify weeds as far away as they can. Then Prather advises them to search in logical spots beyond the edges.

Near Mackay Bar in the Frank Church-River of No Return Wilderness, searchers learned to look for spots where the ground recently slumped. Soil disturbance alone tied in with the presence of rush skeletonweed.

How far to look, Prather said, depends on the weed itself. Some spread by seeds carried in winds.  Whitetop spreads mainly from the roots, and so the search can stay fairly close.

Rush skeletonweed (Chondrilla juncea), a noxious wildfire weed across southern Idaho now spreading north, travels on parachute-like seeds. “Do you have any idea how far we should scout beyond a patch for it?” The question draws laughter and “Trick question!” comment.

“No,” answers Prather. “How far it can go is anyone’s guess.”

Contact Tim Prather at tprather@uidaho.edu.

A canada thistle flourishes near White Bird.
Photo by mark LaMoreuax.

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