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Title: Field evaluation of two endothall formulations for managing hydrilla in Gatun Lake, Panama
Authors: Westerdahl, Howard E.
Keywords: Aquatic plant control
Herbicides
Aquatic weeds
Aquatic plants
Panama Canal
Gatun Lake (Panama)
Aquatic Plant Control Research Program (U.S.)
Publisher: U.S. Army Engineer Waterways Experiment Station
Series/Report no.: Technical Report (Aquatic Plant Control Research Program (U.S.)) ; no.Technical Report A-83-3
Abstract: Aquatic plant coverage of Gatun Lake has steadily i ncreased since completion of canal construction in 1914. Hydrilla (Hydrilla verticillata (L. F.) Royle) and waterhyacinth (Eichhornia crassipes (Mart.) Solms) are the major nuisance plants. Analysis of aerial photographs has shown these plants to have an areal distribution of approximately 5400 ha. In April 1979, a cooperative field study involving Pennwalt Corporation, Panama Canal Commission (PCC), and the U.S. Army Engineer Waterways Experiment Station was initiated in the Frijoles Bay area of Gatun Lake, Panama. The objectives were to: (A.) evaluate the efficacy of two endothall formulations, i. e., Aquathol K and Hydout, for hydrilla control; (B.) determine the effects of each formulation on water quality and the nontarget planktonic community; (C.) evaluate the extent of herbicide dispersion in the test area; and (D.) determine persistence of herbicide residues in water, hydrilla, and sediment within the test plots for supporting Federal registration of Hydout and expansion of the current Federal label for Aquathol K. Three equivalent treatment rates of each formulation were selected for comparison based on a preliminary site survey. The endothall acid equivalent (a.e.) treatment rates were 27, 34, and 50 kg a.e./ha. The treatment rate and formulation combination were randomly assigned to six of eight plots. The remaining two plots were considered as reference areas. Aquathol K and Hydout were effective at controlling hydrilla within the treatment plots. Aquathol K provided control within 24 to 72 hr posttreatment at each application rate; however, Hydout was much slower, requiring 14 to 21 days before hydrilla knockdown was evident at the two higher application rates. The 27-kg-a.e./ha Hydout treatment showed only slight evidence of hydrilla defoliation and biomass reduction prior to plant regrowth to the water surface. No adverse impacts on selected water quality parameters, e.g. dissolved oxygen, pH, water temperature, total Kjeldahl nitrogen, ammonia nitrogen, and total phosphorus, were observed. Only transitory shifts in the plankton community composition and vertical distribution were observed over the 49-day study period. Herbicide dispersion from the treated area was apparent during the first 3 days following treatment. Endothall was detected in the water from the buffer zones of those plots treated with Aquathol K. Negligible endothall residues were found in the buffer zones surrounding the plots treated with Hydout throughout the 90-day posttreatment study period. Persistence of endothall in the water from those plots t reated with Aquathol K and Hydout was less than 7 days. However, endothall persistence from those plots treated with Aquathol K was less than 3 days in sediment and less than 7 days in plant tissue. Endothall levels in sediment and plant tissue from Hydout-treated plots persisted for more than 21 days following treatment. Combinations of Aquathol K and Hydout are recommended as a suitable alternate to copper sulfate for managing hydrilla in Gatun Lake. Although unit costs are approximately five times more expensive for endothall compared to copper sulfate, the lower potential of endothall formulations for toxicity to and accumulation in nontarget organisms following treatment must be considered as well as its long shelf life during storage in this humid, tropical environment.
Description: Technical Report
Gov't Doc #: Technical Report A-83-3
Rights: Approved for public release; distribution is unlimited
URI: http://hdl.handle.net/11681/6393
Appears in Collections:Technical Report

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