Burr Chervil: New Weed Threat Grows from a Humble Start

Burr chervil is a new weed exploding across northern Idaho’s landscape. The weed may offer important clues to the biology of invasive species in general, a University of Idaho scientist says.

A decade ago, burr chervil seemed like it didn’t pose much of a threat, said Tim Prather, a UI weed scientist at Moscow. “We knew of a few plants that grew under hawthorn trees near Lewiston. It just seemed to be sitting there and not doing much.”

That was when Prather was doing graduate work at UI in the early 1990s. After completing his education and starting his career, he returned to UI as an weed science professor in 2000. Burr chervil had changed.“We would find it in places we never expected it while we were looking for other weeds,” Prather said.

Now burr chervil is spreading across wide areas of the lower Clearwater River valley from Lewiston to Lapwai in places where yellow starthistle, a major weed problem, thrives.

More alarming to Prather is that burr chervil is showing up in wetter locales as far north as Latah County north of Moscow.

The weed is a member of the carrot family and is avoided by wildlife and livestock. It is named for its small seeds that are equipped with small hooks, allowing it to easily hitch rides and spread rapidly.

Prather is excited about the potential of the new Center for Research on Invasive Species and Small Populations to help understand burr chervil’s sudden change. “We want to use the sophisticated DNA techniques to see if we can spot genetic changes that allow a population to adapt to its environment and suddenly begin to multiply,” Prather said.

One theory says invasive weeds first enter new habitats in a quiet phase. The plants reproduce for a few generations, during which their genes are effectively shuffled. Like a combination lock, the genetic “tumblers” eventually find the right sequence to fit environmental conditions and the plant multiples rapidly.

Prather wants to go back to the original site of the burr chervil infestation to study the genetic madeup of those plants, then compare it with plants found in new locations.