Management Alternatives

Prevention is the most important management option for Eurasian watermilfoil in Montana. Mapping, monitoring, early detection and eradication are critical to prevention. If a new infestation is found, save a specimen and report the infestation to your county Extension Agent or the Montana Department of Fish, Wildlife and Parks. Inspection and sanitation of recreational equipment will prevent spread. Any aquatic plant debris on boats, trailers, live- wells, boat bilges, and fishing equipment should be disposed of away from lakes, ponds and rivers. Establishing washing stations with sanitation instructions at water-based recreational sites is recommended.

Herbicide^1/

Herbicidal control of Eurasian watermilfoil requires direct application of chemical to water. In Montana, applicators need a 308 Permit (308 Authorization for Emergency Remediation & Pesticide Application) from the Montana Department of Environmental Quality before applying aquatic herbicides to water.

Eurasian watermilfoil is very sensitive to 2, 4-D. Only formulations for submerged aquatic weeds should be used (DMA*4IVM®) and all label requirements must be followed. Consult your local Extension Agent for more information on herbicidal control of Eurasian watermilfoil. The label rate maximum for 2, 4-D is 2.84 gallons/acre-foot of water and rate of application is dependent on water depth. Consult the herbicide label for rates at different water depths. Control is best when applied in early spring or early summer. Re-applications may be needed and should be applied before mid-August.

^1/ Any mention of products in this publication does not constitute a recommendation by the NRCS. It is a violation of Federal law to use herbicides in a manner inconsistent with their labeling.

Mechanical Harvest

Repeated mechanical harvests have been successful in reducing stem densities of Eurasian watermilfoil. However, the risk of spread by stem fragments is high. Using fragment barriers around harvest operations and herbicidal control can prevent spread.

Water drawdown followed by exposure to freezing temperatures for 96 hours will kill plants. This method has reduced infestations, however re-infestation can be rapid.

Biological Control

The watermilfoil moth (Acentria ephemerella = Acentia nevea), native to Europe, is associated with plant declines. The moth was first introduced into the United States in 1927 and it is established in eight eastern and Midwestern states. The larvae feed in and on the stems and leaves, and along with case-making, cause the leaves and stems to fall off the plant. Availability is currently limited. There is also a weevil native to North America, Euhrychiopsis lecontei that is associated with plant declines.

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Last Modified: 02/13/2009