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The residents on Mason Lake in Mason County, Washington have developed an
innovative idea to lower herbicide use and more effectively target small
populations of Eurasian watermilfoil (Myriophyllum spicatum) along the lake
shoreline. Homeowners on Mason Lake have struggled with finding a good chemical
control tool for an early invasion of Eurasian watermilfoil. Mason Lake (over
1,000-acres) has a number of springs and currents and coupled with small patches
of milfoil growing along the shorelines, liquid herbicides have not been
effective because there isn’t enough contact time between the plants and
herbicides. Although residents and their contractors are also hand pulling
milfoil, residents found that in spite of thorough attempts to remove all plants
and fragments, milfoil keeps returning to the same locations year after year.
The residents came up with the idea of creating plastic “tents”, which are
deployed into the water and placed over small clumps of milfoil. They then
inject minute (22 ml/100 ft2) amounts of fast-acting selective herbicide
(triclopyr TEA - Renovate) into the tents, and leave the tents in place for 24
hours. The tents hold the herbicide in contact with the plants for sufficient
time to ensure good kill of the milfoil. Lake residents will be also using other
herbicides such as 2,4-D and fluridone to compare effectiveness between
herbicides.
Lake residents designed and tested several prototypes before settling on the tent-like design pictured at the beginning of this article. They used commonly purchased items such as tent poles, children's' swimming noodles, and gorilla tape to manufacture the tents. The tents are floated out to the milfoil infested area and when placed in position by a diver, they are deployed by removing the floats (pink floats in the photograph). Within a minute or so the tent sinks over the plants and the diver anchors it in place using rocks (if needed).
The diver injects the herbicide through mesh at the top of the tent and then covers the mesh with a plastic flap. The tent is marked with a buoy. After 24 hours the lake residents pull up the tent using the buoy. The tents are designed to be collapsible so they can be easily pulled up by lake residents, stacked on a boat, and redeployed to other sites. Several tents may be needed to cover all the plants at any one site.
A Department of Ecology Aquatic Weeds Management Fund grant is partially funding the work along with in-kind contributions of Mason Lake residents who have devoted thousands of hours to this and other milfoil removal projects.
The chemical company representative initially recommended using a
concentration of 2.0 ppm of Renovate (triclopyr) in the tents. He thought that
the tents would allow more water exchange leading to relatively rapid dilution
of the herbicide within the tents. However, the tents held the concentration
very well and this concentration proved too high (and ineffective in killing the
plants). It is likely the plants shut down rapidly (high concentration and long
exposure) and did not translocate the herbicide. Concentrations of 0.75 ppm and
1.0 ppm triclopyr worked much better. The lake residents reported 100 percent
kill of Eurasian watermilfoil at these lower concentrations.
Questions about this page? Contact Kathy Hamel by e-mail at kham461@ecy.wa.gov
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
