Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2004
Publication Date: 1/21/2005
Citation: Jacobs, J.S., Sheley, R.L. 2005. The effect of season of picloram and chlorsulfuron application on dalmatian toadflax on prescribed burns. Weed Technology. 19(1):59-64. Interpretive Summary: Invasive weeds usually increase after prescribed and wild fires. In some cases, the increase is dramatic. Herbicidal control is critical for managing weeds where prescribed fire is used for rangeland improvement. In this study, we tested two rangeland herbicides typically used for Dalmatian toadflax pre-and post burn. Toadflax was reduced by at least 86% for all picloram and chlorsulfuron treatments. Chlorsulfuron applied in the fall or spring, or picloram applied in the spring effectively controlled Dalmatian toadflax for about three years leaving nutrients released by fire to desirable species.
Technical Abstract: Herbicidal control is critical for managing weeds where prescribed fire is used for rangeland improvement. Understanding the influence on weed control of application season relative to burning is important. Our objective was to determine the effect of picloram and chlorsulfuron on Dalmatian toadflax cover, density, and biomass where these herbicides were applied in the fall before burning, or the spring before or after burning. These seven treatments were applied in a randomized complete block design with four replications at two sites in Montana, USA. Site 1 was treated in fall 1999, spring 2000 pre-burn, burned, and treated again post-burn that same spring. Site 2 was treated in fall 2000, spring 2001 pre-burn, burned, and treated again that same spring. Cover, density and biomass of Dalmatian toadflax were sampled in September 2000, 2001, and 2002 at Site 1 and September 2001 and 2002 at Site 2. Cover, biomass, and density of Dalmatian toadflax were at least 76% lower than that of the control in both spring applied picloram treatments whereas the fall picloram treatment had similar Dalmatian toadflax cover, density, and biomass to that of the control three years after application. Chlorsulfuron reduced Dalmatian toadflax cover, biomass, and density by at least 79% of the control by 2002 in all timings of application at Site 1. At Site 2, Dalmatian toadflax cover, biomass and density were reduced by at least 86% for all picloram and chlorsulfuron treatments in 2002. Chlorsulfuron applied in the fall or the spring, and picloram applied in the spring effectively suppressed Dalmatian toadflax cover, biomass, and density for up to three years leaving sites and nutrients released by fire available to desirable plant species.