Early detection sought for aquatic invasive weed Eurasian Watermilfoil

July 3, 2009

(PhysOrg.com) -- Battling invasive plants is nothing new to Montanans, but a newcomer on the scene dwells in the water. This aquatic invader is called Eurasian watermilfoil. Fortunately, Montanans can take preventive action against this waterborne species, as its distribution across the state is very limited.

"If people plan on boating or fishing throughout Montana and other places in the West this summer, they play an important role in preventing the spread of this noxious weed," said Jane Mangold, Montana State University Extension Invasive Plant Specialist.

Eurasian watermilfoil is one of the most widely distributed of all non-native aquatic plants in the U.S. It was found in Montana in summer 2007, when two populations were found at boat launches in Noxon Reservoir in northwestern Montana. Inventory data collected in 2008 found it in 247 acres in Noxon Reservoir and 117 acres in Cabinet Gorge. A Eurasian watermilfoil task force has been formed to educate Montanans about this plant, test the effectiveness of control methods, and help develop a statewide management plan.

"Because its introduction to Montana is relatively recent and infestations are isolated, early detection is the top priority for management of Eurasian watermilfoil," said Mangold. "Inspection and sanitation of recreational equipment will help to prevent its 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."

Eurasian watermilfoil is a submersed, aquatic perennial that roots to the bottom of water bodies. The fibrous roots are slender and fragile, and leaves are whorled (emerging from the stem at the same level and encircling it) in groups of four. Leaves have 14 to 24 pairs of thread-like divisions giving the leaf a feather-like appearance. Stems can grow up to 21 feet to the water surface, where they branch profusely. Flowers form as spikes at the ends of the branches. They emerge from the water supported by the stem that is typically twice as wide as the lower stem. Pink flower spikes grow 2 to 8 inches long. At the time of flowering, the spike is erect, but bends at fruit set to be parallel to the water surface.

A number of native aquatic plants with fine, feathery leaves in whorls may be confused with Eurasian watermilfoil, including Coon's tail and two native species of watermilfoil: shortspike watermilfoil and whorl-leaf (also known as western) watermilfoil. If you think you may have found Eurasian watermilfoil, contact your county Extension agent or weed district for more information.

"Educate yourself on how to identify Eurasian watermilfoil and ensure that you, your friends, and equipment do not become responsible for its spread. Cleaning watercraft, trailers and fishing gear before leaving the shoreline will help prevent the spread of Eurasian watermilfoil" said Mangold.

The dense weed beds formed by Eurasian watermilfoil have adverse effects on native aquatic vegetation which are important food sources for waterfowl and some mammals. The dense beds can also create habitat for disease carrying insects, including mosquitoes and parasites that cause swimmers itch. Irrigation ditches and equipment, canals, and farm ponds can become clogged by the weed. Management of Eurasian watermilfoil is difficult and expensive due to the environmentally sensitive nature of aquatic habitats.

Herbicidal control requires direct application of chemical to water, which comes with high environmental risk. Eurasian watermilfoil is very sensitive to 2,4-D, and only formulations for submerged aquatic weeds should be used and all label requirements followed. In Montana, applicators need to be in compliance with the Montana Pesticides Act and obtain a 308 permit from the Montana Department of Environmental Quality before applying aquatic herbicides.

Provided by Montana State University (news : web)