EFFECTS OF RODEO(R) AND GARLON(R) 3A ON NONTARGET WETLAND SPECIES IN CENTRAL WASHINGTON

Purple loosestrife (Lythrum salicaria) is an invasive wetland perennia l that became established in northeastern North America in the early 1 800s. Despite its designation as a noxious weed, its distribution has continued to expand. Treatment with herbicides is the most widely used means of controlling purple loosestrife. This study examined the nont arget effects of two herbicides, Rodeo(R) and Garlon(R) 3A, currently used or being considered for use in controlling purple loosestrife in Washington State, respectively. Growth and/or survival of duckweed, Da phnia, and rainbow trout were monitored for at least 24 h following an application of each herbicide. Free-living water column and benthic i nvertebrates were monitored 24 h and 7 d post-spray using activity tra ps and sediment cores. Neither chemical was associated with significan t decreases in survival or growth of the bioassay organisms, with the exception that growth of duckweed was reduced 48 h after exposure to R odeo. Nor were significant decreases in the abundance of free-living a quatic invertebrates detected following the herbicide applications. Re sults suggest that neither herbicide, at the application rates used, p oses a hazard to aquatic invertebrates in wetlands in central Washingt on. However, Rodeo, because it is a broad-spectrum herbicide, may pose a greater hazard to nontarget aquatic vegetation.