Scientists Identify Weevil as Biocontrol for Garlic Mustard

A promising biocontrol agent for garlic mustard, one of the most problematic invaders of temperate forests in North America, has been identified by Agricultural Research Service (ARS) scientists and cooperators.

Garlic mustard, Alliaria petiolata, got its name because its leaves, when crushed, smell like garlic. According to legend, it was brought here from Europe in the 1860s as a culinary herb, but unfortunately, it doesn’t taste very good.

Since then, this invasive weed has spread to 34 U.S. states and four Canadian provinces. It is very difficult to eradicate because its seeds can remain viable in the soil for more than 10 years. A single plant can produce hundreds of seeds, which scatter as far as several yards from the parent. Garlic mustard also releases natural substances called allelochemicals into the soil to suppress growth of other plants.

Ecologist Adam Davis, with the ARS Invasive Weed Management Research Unit in Urbana, Ill., collaborated with colleagues at Michigan State University, Cornell University, the University of Illinois and CABI in Switzerland to create a computer model to simulate the weed’s life cycle.

CABI scientists also found four Ceutorhynchus weevils as potential biocontrol agents for garlic mustard. Davis combined the feeding information of the four candidate weevils and the demographic information on garlic mustard in North America to assess each weevil’s ability to inflict damage on the weed and inhibit its growth. C. scrobicollis came out on top.

The tiny C. scrobicollis only eats garlic mustard. It feeds on the weed’s root crown, the area where nutrients are stored. This stops the flow of nutrients and water from the roots to the rest of the plant. The weevil also damages the meristem, the area where new growth takes place. As a result, garlic mustard produces fewer seeds or, in areas with high weevil populations, dies prematurely without producing any seeds.

C. scrobicollis is currently awaiting release at the University of Minnesota.

Read more about this research in the July 2009 issue of Agricultural Research magazine, available online.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.