2006 / 2007 Milfoil Control Projects

PROJECT ID: 2006 / 2007 Milfoil Control Projects

PROJECT CATEGORY: Aquatic Weed Control

PROJECT LOCATION: Chatcolet, Benewah, Hidden, Round and Coeur d’Alene Lakes (see map below).

SITE CHARACTERISTICS: Aquatic vegetation in general, and aquatic weeds specifically, are found in shallow waters (less than 15 to 18 feet deep) along shorelines and extensively through the Lower Lakes (Chatcolet, Benewah, Hidden, Round Lakes).

PROBLEM DESCRIPTION: Presence of invasive Milfoil species, including Eurasian watermilfoil (Myriophyllum spicatum) and a hybrid (M. spicatum x M. sibericum) in the Lower Lakes and the south end of Coeur d’Alene Lake. If not controlled, these Milfoils will become dominant and form surface mats of thick vegetation. These mats can hinder recreation, degrade fish and wildlife habitat and cause water quality problems.

DESCRIPTION OF FINDINGS: SCUBA diver and rake-throw surveys documented Milfoil locations and densities shown on the map (above) in June and July, 2007. Most of this growth was treated with herbicide or other techniques during July and August, 2007. Further survey work during September 2007 identified additional growth areas along the St. Joe River that needs tyo be treated.

PROJECT GOALS & OBJECTIVES: The primary goal of this project was to initiate the control of Milfoil (M. spicatum and invasive hybrids) in Coeur d’Alene Lake through an integrated treatment program oriented towards eventual eradication of these weeds. Survey and treatment efforts were proposed in the Lower Lakes, where the infestation was first established and a significant source of plant fragments remains, as well as along the shorelines of Coeur d’Alene Lake proper, where moderate to sparse growths were mapped. The secondary goal was to document treatment results so that refinements could be made and a long-term control program developed.

Objectives for the long term were to conduct pre-treatment diver surveys in the Lower Lakes and northwards, along the shorelines of Coeur d’Alene Lake and the St. Joe River (initially starting within Tribal waters), to map the extent of infestation, to implement diver removal, bottom barriers and herbicide applications in specific and appropriate areas, and to monitortreatments in order to better plan subsequent treatments. The work to achieve these goals was intended to continue into the future, with funding support and cooperation from State, Tribal and other sources.


Pre-treatment survey: Tribal divers and support staff spent 13 days inspecting approximately 15 miles of shoreline in Coeur d’Alene Lake and the Lower Lakes (Chatcolet , Round and Hidden Lakes which surround the St. Joe River as it enters the south end of Coeur d’Alene Lake) plus verified milfoil presence in over 300 acres of designated treatment areas.

Herbicide treatment: A contracted herbicide applicator performed a treatment over 366 acres in Chatcolet and Round Lakes using the liquid 2,4-D formulation DMA 4 IVM (EPA Reg. No. 62719-3). An estimated 317 acres showed 100% milfoil removal and an additional 49 acres showed only 60% effective removal due to predominance of a different, possibly hybrid, form of milfoil plus greater water depth that may have reduced herbicide contact with the target plants.

Diver Suction Removal: A contract diver and suction extraction setup mounted on a pontoon barge removed an estimated 3,100 pounds of milfoil from approximately 46 acres. Suction removal was very selective for milfoil and estimated to be 80 to 100% effective in complete removal but had difficulty removing milfoil mixed within dense native plant beds.

Diver hand removal: A small amount of milfoil was removed from the two high-use boat launch / marina areas that were treated. Dense native plant growth again hindered effective removal of EWM mixed within other plants. The effectiveness of this effort was estimated to be less than 50% in this situation.

Public Education / awareness: The public outreach portion of this project was focused on the planned herbicide treatment and utilized newspaper articles, presentations to lakeshore property owners groups, public notices, direct mailings and dock posting. Most responders expressed support for the project.


Pre-treatment survey: The pre-treatment diver survey took the better part of two months (30 actual days) during which two contract divers, the Tribal Project Lead / boat operator and a GPS Technician mapped Milfoil presence in most of the 3,000 acre Lower Lakes area and over 25 miles of Coeur d’Alene Lake shorelines. In addition, Tribal staff collected rake survey data at 298 GPS points assigned by ISDA as part of the project Monitoring and Evaluation effort.

Herbicide treatments: A total of 599 acres of moderately dense Milfoil growth were treated with herbicides during August this year. Two herbicides were used for this, the liquid 2,4-D formulation DMA 4 IVM® in areas approximately eight feet deep or less, and the granular 2,4-D formulation Navigate® in deeper areas. The effectiveness of the liquid treatment was fairly good with an estimated efficacy of 88%. The effectiveness of the granular treatment, however, was poor with an estimated efficacy of only 43%. The greater depths and dominance of hybrid Milfoil in the granular areas are suspected to influence these results. However, the observation of standing Milfoil plants in portions of both treatment areas was the most obvious sign that effectiveness was not up to the level expected.

Bottom Barrier placement: Following research work performed by the University of Idaho for the Idaho Milfoil Task Force in 2005 and 2006, this treatment used 20 barrier panels, each 10 ft x 10 ft with a PVC pipe frame, which were placed by a diver and left in place for over 10 weeks. The installation was performed on July 19 in conjunction with the visit by the ISDA Director and staff to Tribal waters. The treatment did control 100% of the Milfoil which was under the barrier panels but there was some Milfoil growth which remained outside the barrier areas.

Diver hand removal: Diver hand removal of Milfoil was performed for this project by contract divers and by Tribal staff. As with last year’s effort, this work was hindered where the water clarity was poor and where dense native plant growth made it difficult to find and remove the Milfoil roots. In any event, nine bags of Milfoil material was removed, weighing approximately 300 pounds from a total area of approximately 1.5 acres. The overall effectiveness was estimated to be between 50% and 80% depending on the area.

Post-treatment Survey: The post-treatment work focused on the completion of the rake survey of ISDA points and this effort was of key importance in estimating the effectiveness of the herbicide treatments. However, diver and boat inspections of areas of the St. Joe River pointed out the presence of up-stream sources of Milfoil fragments and also the need for river-bank treatments.

Public Education/awareness: This portion of the project focused on a Milfoil awareness presentation to a lakeshore property owners association, mailing of notices regarding the planned herbicide treatment to landowners, publication of herbicide notices in a local newspaper, posting of herbicide treatment notices on docks in the treatment areas and public accesses and the development of a Milfoil brochure.

PROJECT TIMELINE: Milfoil survey and control work was performed during June through September in2006 and 2007. The project report for each year was completed by November 30.