Netherland, M.D., W.R Green, and K.D. Getsinger, 1991. Endothall Concentration and Exposure Time Relationships for the Control of Eurasian Watermilfoil and Hydrilla, US Army Corps of Engineers.

Reprinted with Permission from Journal of Aquatic Plant Management (1991) 29: 61-67

Endothall Concentration and Exposure Time Relationships for the Control of Eurasian Watermilfoil and Hydrilla

Abstract
Herbicide concentration and exposure time relationships were determined for endothall (the dipotassium salt of 7-oxabicyclo [2,2,1] heptane-2,3- dicarboxylic acid) and control of Eurasian watermilfoil (Myriophyllum  spicatum L.) and dioecious hydrilla (Hydrilla verticillata L. F. Royle) under controlled-environment conditions. Sixteen endothall concentration and exposure time combinations were tested for Eurasian watermilfoil: concentrations ranged from 0.5 to 5.0 mg acid equivalent (ae)/1; exposure times ranged from 2 to 72 hr. Twenty-seven endothall concentration and exposure time combinations were tested for hydrilla: concentrations ranged from 1.0 to 5.0 mg ae/1; exposure times ranged from 6 to 72 hr. Plant control was based on shoot and root biomass harvested at the end of the experiments. Weekly visual injury ratings were used to characterize efficacy during the course of the experiments. Plant control increased (biomass decreased), as either concentration or exposure time increased. A threshold level was reached in which a concentration/exposure time combination provided satisfactory control. Severe Eurasian watermilfoil injury (> 85% biomass reduction) occurred when exposed to 0.5 mg ae/1 for 48 hr, 1.0 mg ae/1 for 36 hr, 3.0 mg ae/1 for 18 hr, and 5.0 mg ae/1 for 12 hr. Severe hydrilla injury (> 85% biomass reduction) occurred when exposed to 2.0 mg ae/1 for 48 hr, and 3.0, 4.0 and 5.0 mg ae/1 for 24 hr. The 1.0 mg ae/1 treatment failed to produce severe hydrilla injury at the maximum exposure time tested of 72 hr. Increased control of Eurasian watermilfoil and hydrilla is likely for treatments in systems where plants remain in contact with endothall concentrations and exposure times greater than the developed threshold levels.

Entire Paper
Contact: Kurt Getsinger, US Army Corps of Engineers, Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180
Key Words: Eurasian_watermilfoil, Hydrilla, Chemical_control
Product Type: Research, Control
User Type: Resource Management