Management of Eurasian Watermilfoil In Long, Mickey and Ruth Lakes
Eurasian Watermilfoil was first observed in Mickey Lake in 1995. It has expanded to several sites and has fluctuated to between 70 and 85 sites since 2001. In 2001, the Long Lake Association estimated that 26 acres of the lake were infested with EWM. As of 2009 there is less than a combined total of 10 acres of EWM in Ruth, Mickey and Long Lakes. EWM infestations are recorded and monitored on a regular basis. Long, Mickey and Ruth Lakes comprise approximately 3,000 acres of water surface of which nearly 1,400 are able to support aquatic rooted plants by depth. Macrophyte studies conclude Long Lake to be an oligotrophic body and not able to support vast amounts of plant life, as evidenced by the relatively low amount (approximately 55 acres) of all rooted aquatic plants.
There are three methods currently being incorporated in the control of EWM in our lakes. Chemical application began in 1996 and has been used in most years since. MidFoil® or weevil plantings began in 2002 and most years through 2007. Manual harvesting by diving has been successful in the shallow end of Mickey Lake. All of these methods have their pros and cons. Chemical treatment has predictable results with immediate short term, near complete elimination of the EWM infestation. There is ongoing debate over the long term ecological and health risks. EWM can build a resistance to chemicals, thus requiring stronger future applications. Weevils are indigenous to North American lakes and do not require DEQ permits or permission of the riparian and have no health or ecological concerns. They usually do not completely eliminate the infestation and may not prevent an infestation from expanding in size. Manual harvesting completely eliminates the plant along with the root system. However, it is very labor intensive and not practical for large or deep infestations.
An integrated pest management program has evolved over the years with respect to the observed results of the treatment methods. With the use of chemicals, desired results have been achieved in most cases with initial and 1 or 2 follow up treatments. It allows for relatively quick clearing of EWM where recreation is impeded. Re-infestation occurs in 2-4 years in most cases. Ten sites have been planted with weevils since 2002 with positive results in approximately 65% of the planted sites. Monitoring studies show that weevils have spread to a significant number of non-planted EWM sites. Weevils keep EWM infestations cropped so it will not impede recreation. Diving is a practical method to keep small EWM sites from advancing in shallower areas that have greater levels of nutrients.
Attached is a PDF of the known existing stands of milfoil in Long, Mickey, and Ruth Lakes. The tally from the map as marked is 6.5 acres and being that it is constantly changing it is safe to say we have less that 10 acres of milfoil in the lake. We have been maintaining this level for at least the last 5 years. Estimates in previous years exceeded 26 acres of EWM.
The map shows the 10 sites where weevils have been planted and they all have a prefix of “S.” Sites 1-4 were planted in 2002 and 2003. The remaining sites were added subsequent years, the last being 2007. Of those sites we have had about a 65% success rate.
In 2009 we did a survey of 35 EWM sites that represented over 90% of the milfoil in the lake. The results showed weevils in 29 of the 35 sites or about 83% of the sites. We believe the weevils are playing a significant role in the control of the milfoil. We also believe the characteristics of Long Lake will support very little milfoil as evidenced by the macrophyte surveys showing approximately 50 acres of all rooted aquatic plants in Long Lake.
Eurasian Watermilfoil Locations 9-23-10
A complete Weevil Survey Report is available upon request. Use the contact page to send the request.