Lake St. Helen is a 2,400 acre public lake located in Roscommon County, Michigan. EnviroScience, Inc. began a five-year weevil stocking program in 1998. At the start of the project an estimated 70% of the lake was covered with topped-out milfoil.

During the first year of the project, a total of 13,500 weevils were stocked in four Eurasian watermilfoil (EWM) beds. Four additional sites were established to monitor the weevil progress. Prior to stocking, the EWM stems were beginning to form a mat on the surface of the water and the plants were healthy. Although the water level had dropped forty centimeters by the time of the follow-up survey, twelve weeks after stocking the EWM plants in the sites, the EWM was below the water surface, indicating the weevils had begun to control the EWM. The weevil density also increased in most sites over the course of the first summer. Initial data indicated the 1998 stocking event was successful and the establishment of a stable weevil population had occurred.

At the time the June 1999 stocking event, EWM in the 1998 stocking and monitoring sites had virtually disappeared. An additional 16,000 weevils were stocked in six other areas of the lake. By the time of the second year's follow-up survey in August of 1999, many native species were present that were not in June. Coontail, Water lilies, American waterweed, Chara, Floating pondweed and various other Pondweed species were all reappearing. Three of the beds stocked in 1999 had been heavily damaged by weevils, while the remaining three sites suffered moderate damage.

An additional 14,000 weevils in five sites were stocked in June of 2000. By the time of the follow- up survey in August of 2000, one of the June stocking sites had virtually disappeared. The remaining stocking sites were either heavily damaged or moderately damaged indicating the weevils were healthy and controlling the EWM. There was also an overall increase in weevil densities over the summer of 2000. More native plant species were also returning. Robbins pondweed (a desirable native species) was not present prior to stocking in June, but was observed in August.

Lake St. Helen received an additional 19,000 weevils in May of 2001. The previous years' stocking sites (1998-2000) had virtually disappeared, therefore five new stocking sites were established. By the time of the follow-up survey in August of 2001 most of the stocking sites were extremely damaged and patchy. What little EWM that remained was approximately three feet from the water surface and losing buoyancy. Adults and larvae were present and having a dramatic effect on EWM.

The stocking of 62,500 weevils from 1998 through 2001 has resulted in heavy damage to all EWM beds in Lake St. Helen. Weevils had increased in density from 1999 to 2000 and also over the course of the summer of 2000 and 2001, indicating that a stable population of weevils was established and is thriving in the lake. As has happened in the past, several beds stocked during the first two years of the project had been decimated by the summer of 2001. There is a healthy community of native aquatic plants in Lake St. Helen. These native species should continue to increase the likelihood of a EWM decline as they begin to compete with the milfoil for resources. The overall data indicate that all four years of stocking have been successful. The weevil population is thriving and stabilizing, indicating that the MiddFoil® program in Lake St. Helen has been a complete success and will continue to be successful in the future.

In 2007, EnviroScience commissioned an independent follow-up survey of the lake by a third party environmental firm. This survey found that although milfoil was found in approximately one quarter of the 345 grid points sampled, the milfoil was generally very sparse. In contrast to the situation in 1998 where milfoil covered approximately 70% of this 2,200 acre lake, milfoil occupied approximately 50 total acres at the time of the 2007 survey. Less than 5 acres of that was topped out on the surface. A highly diverse and healthy native plant community containing 22 species was found and the consultant noted that these plants serve an important role in minimizing the spread and recolonization of milfoil. Although the consultant recommended that the association consider stocking additional weevils, to date, the association has not seen the need to do so.

For additional information regarding Lake St. Helen and its implementation of the MiddFoil® process, please contact Mr. John Bawol with the St. Helen Lake Association listed to the left.