Evaluation of Aquathol K Efficacy on Sago Pondweed in the Ogilvy Ditch

The Ogilvy Ditch and Land Company (ODLC) located in Weld County, near Greeley, Colorado, is experiencing flow restriction in their primary irrigation canal due to a severe infestation of sago pondweed (Stuckenia pectinatus), a native plant species to North America. The U.S. Bureau of Reclamation, Environmental Applications and Research Group, of the Technical Service Center in Denver, Colorado and Uniphos Agro-Chemical Industry (Uniphos) offered to help the ODLC with their aquatic weed problem. Uniphos is seeking to register Aquathol K products in the 17 western states for use on irrigation canal systems. This was a cooperative study between Reclamation, Uniphos and the ODLC and was of benefit to all three parties. One formulation that is being considered for registration is Aquathol K (dipotassium salt of endothall) to provide control of sago pondweed and other rooted macrophytes in irrigation canals in the 17 western states. Aquathol K has the current EPA Registration No. 4581-204 and is currently registered as an aquatic herbicide for use in ponds and lakes, where the water can be controlled, by the Environmental Protection Agency (EPA) but it is not register for use in primary irrigation canals. The U.S. Army Corps of Engineers, at the Waterway Experiment Station in Vicksburg, Mississippi, is also involved in this research and has been developing laboratory data on concentration and exposure rates of various herbicides used on sago pondweed including Aquathol K an endothall compound. During this study, it was the responsibility of the Bureau of Reclamation to evaluate the efficacy of Aquathol K, monitor the exposure times during the application and monitor the water quality of the canal. Uniphos set up an herbicide injection system and collected water samples to be analyzed for herbicide concentration. Crop tolerance data (collected during other studies in other locations), water residues, and efficacy data will all be submitted to E.P.A. as part of the registration package for using endothall products in irrigation systems in the 17 western states.