Evaluation of Eurasian Watermilfoil Control Techniques Using Aquatic Herbicides in Fort Peck Lake, Montana.

摘要

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 ( g/L); Rock Creek South, endothall at 2500 g /L, triclopyr at 2000 g /L; Rock Creek North, endothall at 2000 g/L, 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 g/L 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.