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Efficacy of Combinations of Endothall with 2,4-D and Triclopyr for Enhanced Control of Eurasian Watermilfoil with Low Contact Time.

Madsen, J. D., Wersal, R. M., & Getsinger, K. (2009). Efficacy of Combinations of Endothall with 2,4-D and Triclopyr for Enhanced Control of Eurasian Watermilfoil with Low Contact Time. Midwest Aquatic Plant Management Society 29th Annual Meeting, March 1-4, 2009. Chicago, IL.

Abstract

Eurasian watermilfoil (Myriophyllum spicatum L.) is a widespread nuisance problem in the United States, which is manageable in most aquatic systems with a suite of approaches. One remaining problematic habitat for managing Eurasian watermilfoil is those areas with high water exchange rates, which results in low potential contact time for herbicides. Over the past several years, we have been examining the use of herbicide combinations. By combining a contact herbicide (endothall) with systemic herbicides (either 2,4-D or triclopyr), the efficacy and long-term control of the contact herbicide is enhanced while the required contact time for the systemic herbicides are reduced. We performed mesocosm tank studies that demonstrated enhanced control of Eurasian watermilfoil using endothall with 2,4-D or triclopyr under varying contact times. In the first study, we observed 90% control in treatments of 2ppm 2,4-D and 1ppm endothall at both 48 and 24 hours, and better than 70% control with concentrations as low as 0.5ppm 2,4-d with 0.25ppm endothall at 24 hours. In the second study, we found enhanced control at 1ppm endothall and 0.5 to 0.125ppm triclopyr with 12 to 24 hours exposure, as compared to triclopyr alone at those concentrations. Treatments with 6 hours exposure resulted in poor control. Initial field trials in Pend Oreille Lake, Idaho resulted in significant reductions in Eurasian watermilfoil after treatment. Combinations of a contact herbicide (endothall) with a systemic herbicide (2,4-D or triclopyr) will results in enhanced control of Eurasian watermilfoil in environments with low exposure time or high water exchange rates.


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