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WSU/Pend Oreille Extension introduced the Sense of Place series in 1999, with a focus on local landscape and natural history of Pend Oreille County, Washington. A partnership with the Kalispel Tribe of Indians Natural Resources Department has allowed us to expand this program through EPA funding to include more classes, a newsletter and this website.

How to Recognize the Evil Twin...

Count the Leaflets


by Sharon Sorby

Northern milfoil (Myriophyllum sibiricum) is a native plant that commonly grows in lakes, rivers and ponds throughout Washington. Like other aquatic milfoils, it has feather-like leaves below water, and flowers and tiny leaves arranged on emergent stalks. Northern milfoil can often resemble and be confused with Eurasian milfoil. In general however, northern milfoil tends to be a more robust plant and has fewer and more widely spaced leaflet pairs than Eurasian milfoil. Northern milfoil is a desirable species, providing cover for fish and invertebrates. It supports insects and other small animals; waterfowl occasionally eat the fruit and foliage.

Eurasian milfoil (Myriophyllum spicatum), is one of the worst aquatic plant pests in North America. It spreads fast through fragmentation—a tiny sprig dropped into a clear waterbody can soon become a milfoil jungle. By late summer in 1982, Eurasian milfoil covered approximately 200 acres of the Pend Oreille River. By 1988, it had infested over 2400 acres. Eurasian milfoil looks so much like its native relative, northern milfoil, that it was once thought to be a variety of that species. Often even milfoil experts must rely on pigment or DNA analysis to distinguish milfoil species from each other. But most of time (70%), submersed Eurasian milfoil leaves have more than 14 leaflet pairs, while the northern milfoil has less than 14 leaflets per leaf.

Milfoil Management Plan

In cooperation with Public Utility District Number 1 (PUD), the County Weed Board has developed an interim Integrated Aquatic Vegetation Management Plan to guide milfoil control actions on the Pend Oreille River while maximizing limited resources.

The plan will be introduced for public comment on November 13, 2003 at a public workshop (see page 4), or pick up a copy at the Extension Office, 419 S. Scott. There will be a three-week comment period and the comments will be incorporated into a final draft to be presented to the Board of County Commissioners by mid-December.

The control portion of the plan focuses on the current Aquamog operation with discussion of other methods and options. Currently, the crew operates the machine four ten-hour days per week throughout the year. Down times occur in the events of the river icing over, extremely low temperatures (the hydraulics won’t work), equipment repair and maintenance, high water during spring run-off and days when the operators assist in large terrestrial weed control projects. We try to limit time off the machine for these projects to one day per week.

The Aquamog has two attachments to effect milfoil control. The tiller attachment is used approximately nine months of the year. It is effective at removing plant roots from around docks, swim beaches and other areas. The rake attachment is used approximately three months of the year, when plant beds become dense, clogging boat access and diminishing fishing and swimming enjoyment. It is effective at removing plants and roots from large areas at a more rapid rate than the tiller can accomplish. However, it cannot clean up around docks as closely as the tiller and control in other areas can be patchy.

The other management options discussed in the plan include biological control, herbicide treatments and landowner scale methods such as commercial harvesting, bottom barrier installation, weed cutting or raking and weed rolling. Currently, the use of herbicides is limited by the nature of the river’s flowing water and the state DOE for use within the Management Reach. A goal of the plan is to identify areas appropriate for herbicide control, contact the affected landowners and solicit their cooperation in organizing an herbicide application. The County would collect the fees associated with the work and contract out the application. Landowner scale options will be promoted through educational presentations and personal contacts between riverfront owners and Weed Board staff.


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