Preemergence Control of Nine Invasive Weeds with Aminocyclopyrachlor, Aminopyralid, and Indaziflam

Abstract

There are an estimated 400 million hectares of non-cropland in the United States primarily designated as rangeland and pastureland, and there are more than 300 invasive weeds found on these sites, causing an estimated annual loss of $5 billion. Among the most invasive and problematic weeds are Dalmatian toadflax, diffuse knapweed, downy brome, and musk thistle. Currently, herbicides are the most common management strategy for broadleaf weeds and invasive winter annual grasses. Indaziflam, a new herbicide for invasive plant management in non-crop areas, is a cellulose-biosynthesis inhibitor capable of providing residual invasive winter annual grass control up to 3 yr after treatment (YAT). A field experiment was conducted to determine whether residual Dalmatian toadflax and downy brome control by aminocyclopyrachlor, imazapic, and picloram could be extended by tank mixing these herbicides with indaziflam. Indaziflam tank mixed with aminocyclopyrachlor, imazapic, and picloram provided increased Dalmatian toadflax (84% to 91%) and downy brome (89% to 94%) control 4 YAT, compared with treatments excluding indaziflam. Treatments without indaziflam controlled 50% to 68% of Dalmatian toadflax and <25% downy brome 4 YAT. Based on these results, a greenhouse dose–response experiment was conducted with aminocyclopyrachlor, aminopyralid, and indaziflam to compare preemergence control of nine common non-crop weeds. Averaged across species, aminocyclopyrachlor and aminopyralid GR50values (herbicide concentration resulting in 50% reduction in plant biomass) were 29 and 52 times higher compared with indaziflam, respectively. These data suggest that indaziflam could be used for residual control of non-crop weeds as a tank-mix partner with other foliar-applied broadleaf herbicides.