University of California

Aerial application of clopyralid demonstrates little drift potential and low toxicity to toads


Joseph M. DiTomaso
Jessica R. Miller
Guy B. Kyser
Art W. Hazebrook
Joel Trumbo
David Valcore
Vanelle F. Carrithers

Authors Affiliations

J.M. DiTomaso is Non-Crop Extension Weed Ecologist, Department of Vegetable Crops, UC Davis; J.R. Miller is Graduate Student, Department of Vegetable Crops, UC Davis; G.B. Kyser is Staff Research Associate, Department of Vegetable Crops, UC Davis; A.W. Hazebrook is Land Rehabilitation and Maintenance Coordinator, Center for Environmental Management of Military Lands, Colorado State University, Fort Hunter Liggett; J. Trumbo is Environmental Scientist, California Department Fish and Game (DFG), Rancho Cordova; D. Valcore is Senior Research Scientists, Dow AgroSciences, Indianapolis; V.F. Carrithers is Senior Research Scientists, Dow AgroSciences, Indianapolis.

Publication Information

Hilgardia 58(3):154-158. DOI:10.3733/ca.v058n03p154. July 2004.

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The herbicide clopyralid (Transline) is commonly applied by air to control yellow starthistle, a noxious weed, in California. In laboratory studies, clopyralid toxicity in Fowler's toad was low, indicating a wide safety margin when used under field conditions. In addition, monitoring of clopyralid drift following aerial application demonstrated that 98-foot (30-meter) buffers between treatment areas and water sources provided adequate drift protection for an adjacent stream and vernal pools. Nevertheless, to ensure that movement of the herbicide to water sources is minimized, it is important to prevent application error, particularly accidental encroachment into established buffer zones. This study demonstrated that drift potential for clopyralid was minimal even with an aerial application and a slight downwind breeze toward sensitive aquatic sites. It is also the first report demonstrating a high tolerance to clopyralid in larval toads.


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DiTomaso J, Miller J, Kyser G, Hazebrook A, Trumbo J, Valcore D, Carrithers V. 2004. Aerial application of clopyralid demonstrates little drift potential and low toxicity to toads. Hilgardia 58(3):154-158. DOI:10.3733/ca.v058n03p154
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