Considering Alternative Strategies: Weevils and Herbicides

Besides hand picking, suction harvesting, bottom barriers, and benign neglect, there are two noteworthy ways of dealing with milfoil infestation that have been tried recently in nearby lakes.

TriclopyrThis summer our sister lake received permission to begin using the herbicide triclopyr to kill milfoil in their lake. The applications will continue over the next few years, and traditional harvesting measures have to continue. Nonetheless some Lake Morey residents are already declaring the experiment a success.

Beginning in Fairfield Pond2005 tiny herbivorous insects were introduced into Fairfield Pond (near St. Albans) to eat the milfoil growing there. They are Euhrychiopsis lecontei, commonly known as milfoil weevils, which are a native insects that normally feed on native Northern milfoil plants. Fairfield residents are happy with the results to date.

As a result your Lake Fairlee Association board members have been asked with increasing frequency whether and when we will be undertaking one or the other of these tactics. This blog entry is my attempt to answer those questions.

First some general observations. Our association was formed to preserve and enhance the natural beauty of Lake Fairlee. Our bias is in favor of keeping the lake “natural.” We are well aware of the “law of unintended consequences” which frequently plagues those who attempt to combat one outside invading species by introducing something else. And we are cautious, not likely to try anything that has not been tried and proven elsewhere.

weevil adultBoth chemical treatments and weevils are relatively new, at least in Vermont. We are somewhat skeptical of the glowing early reports, as they come from those who are invested in each “solution.” It is only natural that well meaning lake associations, once they have decided to adopt a program, tend to focus on the beneficial aspects.

On the other hand, we understand that our milfoil problem will not go away. No amount of suction harvesting and bottom barriers will remove all the milfoil from our lake once and for all. renovate otf bag Indeed, if it magically happened that one day all the milfoil were gone, it would likely be just a matter of time before milfoil would be reintroduced and begin to spread again. I liken milfoil to crabgrass or mosquitoes. They must be contended with but we cannot expect ever to be finally rid of them.

Therefore we are glad for the experiments of other lakes. We will watch their progress and study their results. The State of Vermont is also studying and evaluating these strategies, as their permission is required for chemical or weevil treatment (as well as for suction harvesting and bottom barriers). For the time being we will continue to harvest milfoil and to slow its spread with bottom barriers, which are effective and necessary, but not final.

Following are some links to more information about milfoil eating weevils and the herbicide used in Lake Morey.
Chemical treatment

LINK Wikipedia article on triclopyr

LINK The full text of Lake Morey’s herbicide permit (32 pages)

News coverage of Lake Morey’s chemical treatment application, before and after:

  • LINK February 2007 article in Bradford Journal Opinion
  • LINK July 2007 article in Valley News


LINK The University of Minnesota has excellent coverage of the milfoil weevil

LINK The University of Florida milfoil/weevil page

LINK The Vermont Agency of Natural Resources still considers weevil treatment of milfoil infestation to be “experimental” and will not help pay for its use although there are efforts to change this.

Weevils in the news:

  • LINK September 2007 article in the Boston Globe
  • LINK September 2007 article in Burlington Free Press
  • LINK September 2007 Weevil success in a Michigan lake