Aquatic Plant Control Research Program: 2,4-D Concentration and Exposure Time Relationships for the Control of Eurasian Watermilfoil

Abstract : Herbicide concentration and exposure time relationships were developed for 2,4-D and the control of Eurasian watermilfoil (Myriophyllum spicatum L.), under laboratory conditions using concentrations, exposure times, and biomass similar to field conditions. Fourteen 2,4-D concentrations (0.5,1.0, and 2.0 mg acid equivalent (ae)/l) and exposure time (12, 24, 36, 48, 60, and 72 hr) combinations were tested. Eurasian watermilfoil control was based on plant injury incurred, relative to that of untreated plants, and harvested biomass (4 weeks after treatment). Plant injury increased with increasing concentrations and exposure times to a threshold above which control was achieved. Severe Eurasian watermilfoil injury occurred in the 0.5 mg ae/l for 72-hr, 1.0 mg ae/l for 36-hr, and 2.0 mg ae/l for 24-hr exposures. Eurasian watermilfoil control was established in the 1.0 mg ae/l for 48 hr, and 2.0 mg ae/l for 36-hr, and 48-hr exposures. Control can be predicted for Eurasian watermilfoil treatments in both dynamic and static aquatic environments when plants remain in contact with 2,4-D concentrations greater than the developed threshold levels. Aquatic plant control, Eurasian watermilfoil; Herbicides.