PEST STATUS OF WEED

obligate biennial herb, is currently one of the most serious invaders in forested areas of the northeastern and midwestern United States. Alliaria petiolata is one of the few non-indigenous herbaceous species able to invade and dominate the understory of North American forests. Garlic mustard is not known as a weed on other continents. 1997; Meekins and McCarthy, 1999). Garlic mustard invades sites independent of presence or cover of native species, and species-rich sites are more likely to be invaded than species-poor sites (Nuzzo, unpub. data). Once established, A. petiolata becomes a per-manent member of the community, steadily increas-ing in presence but with large annual fluctuations in cover and density (Byers and Quinn, 1998; Nuzzo, 1999; Meekins, 2000). Long-term presence of garlic mustard was associated with a significant decline in cover of native perennial herbaceous species (Nuzzo, unpublished data). Phytotoxic chemicals produced by A. petiolata may interfere with growth of native species, potentially through inhibition of mycorrhizal activity (Vaughn and Berhow, 1999)