Evaluation of Eurasian Watermilfoil Control Techniques Using Aquatic Herbicides in Fort Peck Lake, Montana
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS ENVIRONMENTAL LAB
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In 2012, field trials were conducted in Fort Peck Lake to evaluate herbicides for controlling Eurasian watermilfoil and to provide management guidance. Plots of 1 to 3 hectares were treated with the herbicides Dredge Cut, endothall at 2000 micrograms per liter gL Rock Creek South, endothall at 2500 g L, triclopyr at 2000 g L Rock Creek North, endothall at 2000 gL, triclopyr at 2000 g L Reference, no herbicides using a variable-depth application technique. The Dredge Cut was an open-water site protected with a barrier curtain to sequester water exchange, where endothall wase maintained 1500 gL for 24 hours after treatment HAT, providing 96 control of milfoil by 4 WAT but only 22 control at 50 WAT. Rock Creek South was an open-water plot where water exchange processes diluted herbicide levels endothall 300 g L and triclopyr 500 g L by 6 HAT, and milfoil control was limited to 7 at 4 WAT and 99 control at 50 WAT. Limited water exchange processes in Rock Creek North resulted in slow dissipation of herbicides endothall 700 g L and triclopyr 800 g L for 24 HAT, and milfoil control was 100 at 4 and 50 WAT. Periods of low water levels in the lake impacted the 50 WAT efficacy results in plots above the dam. Native vegetation was sparse in all plots but survived treatments with an increase in species diversity at 50 WAT. Treatments had no impacts on water quality including dissolved oxygen levels. Adequate control of milfoil can be achieved in areas of the lake where water exchange processes are reduced and herbicide concentrations surrounding target plant stands can be maintained.
- Agricultural Chemistry
- Hydrology, Limnology and Potamology
- Water Pollution and Control
- Pesticides Pollution and Control