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Journal of Aquatic Plant Management 42: 103.

"Carfentrazone-ethyl Pond Dissipation and Efficacy on Floating Plants"

Tyler J. Koschnick, W.T. Haller and A.W. Chen

ABSTRACT

Carfentrazone-ethyl (CE) is a reduced risk herbicide that is currently being evaluated for the control of aquatic weeds. Greenhouse trials were conducted to determine efficacy of CE on water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.), water lettuce (Pistia stratiotes L.), salvinia (Salvinia minima Baker) and landoltia (Landoltia punctata (G. Mey.) Les & D. J. Crawford). CE controlled water lettuce, water hyacinth and salvinia at rates less than the maximum proposed use rate of 224 g ha-1. Water lettuce was the most susceptible to CE with an EC90 of 26.9 and 33.0 g ha-1 in two separate trials. Water hyacinth EC90 values were calculated to be 86.2 to 116.3 g ha-1, and salvinia had a similar susceptibility to water hyacinth with an EC90 of 79.1 g ha-1. Landoltia was not adequately controlled at the rates evaluated. In addition, CE was applied to one-half of a 0.08 ha pond located in North Central, Florida to determine dissipation rates in water and hydrosoil when applied at an equivalent rate of 224 g ha-1. The half-life of CE plus the primary metabolite, CE-chloropropionic acid, was calculated to be 83.0 h from the whole pond, and no residues were detected in water above the limit of quantification (5 ?g L-1) 168 h after treatment. CE dissipated rapidly from the water column, did not occur in the sediment above the levels of quantification, and in greenhouse studies effectively controlled three species of aquatic weeds at relatively low rates.