Chemical Treatment at Mineral Lake, Tuesday, August 31, 2021.

UPDATE! This treatment was conducted on Tuesday, August 31, 2021. We expect to see a decline in the Eurasian watermilfoil over the next few of weeks. We thank the community of Mineral for their support and we thank our partners for working with us to get this treatment funded and completed!

The Lewis County Noxious Weed Control Board has been granted coverage under the Washington State Department of Ecology Aquatic Plant and Algae Management General Permit WAG994515 to treat Mineral Lake with an aquatic herbicide to control Eurasian watermilfoil, a Washington State class B aquatic noxious weed.

Understandably, community members may have questions and concerns about this treatment. We've complied a list of commonly asked questions that we hope will address most, if not all your concerns. We encourage you to contact our office at #(360) 740-1215 if you have any additional thoughts you'd like to discuss.

Eurasian Water Milfoil floating.jpg

Why are you treating Mineral Lake with a chemical herbicide?

Lewis County Noxious Weed Control staff first observed Eurasian watermilfoil, a Washington State class B noxious weed, growing in Mineral Lake in the fall of 2020. What we know from past infestations in Washington State waters, is that this species is an aggressively invasive weed that can rapidly disrupt a lake's ecosystem and ruin a water body in as little as 2 years. Due to the extent of the infestation, the lake-wide distribution, and the vulnerability of Mineral Lake, Lewis County Noxious Weed Control believes that an expeditious herbicide treatment of the milfoil would be the best management decision to protect the lake ecosystem, recreational users, and the surrounding community.

What chemical will be used and what are the associated risks?

ProcellaCOR EC (Florpyrauxifen-benzyl) is a selective aquatic herbicide that has been used very successfully to treat Eurasian watermilfoil in Washington State. This herbicide has been approved by the federal Environmental Protection Agency and the Washington State Department of Agriculture as a reduced risk aquatic herbicide. ProcellaCOR also has no restrictions on recreation, fishing, or potable water use. There is, however, a 24 Hour irrigation restriction for landscapes, crops, and pastures. The mode of action is absorption by the target species (milfoil) through its leaves and disruption of the photosynthetic cycle. The herbicide acts quickly, being absorbed by the weed in less than 30 minutes. What is not absorbed by the weed quickly begins to degrade after 30 minutes. There is also no bioaccumulation of this herbicide in fish and other aquatic organisms which makes the fish harvested safe for consumption.

ProcellaCOR was recently used by AquaTechnex, LLC. to treat a heavy infestation of watermilfoil in Vancouver Lake with fantastic results. You can learn more about AquaTechnex and their use of ProcellaCor in the Pacific Northwest by watching a great presentation available here

Technical information for Florpyrauxifen-benzyl is available from Washington State Department of Ecology by visiting their website

The Environmental Impact Statement is very detailed, but can also be quite technical. Another source of information that might be helpful are fact sheets about these chemicals available from the Wisconsin Department of Natural Resources:

Again, please note that information about ProcellaCOR EC is listed under the active ingredient “Florpyrauxifen-benzyl”.

Can't the milfoil just be removed by hand?

Yes and no. There are mechanical and manual control measures that could be taken to reduce the current abundance of the watermilfoil, however, at the time of discovery in the fall of 2020, the watermilfoil was positively identified around the entire lake perimeter. Also, due to the propensity of watermilfoil to fragment when disturbed, it is not feasible to try to remove the watermilfoil by hand and expect to achieve adequate long term control.

Where will the herbicide be applied?

As mentioned previously, the Eurasian watermilfoil has been documented along the entire perimeter of the lake. Contract applicators will deliver herbicide by boat to all locations where milfoil is observed, which is likely to encompass the nearshore littoral zones of the lake.

When will this herbicide treatment happen?

Time is of the essence when it comes to treating the Eurasian watermilfoil. While we had hoped to treat the milfoil in early July, funding and permitting processes took long than we anticipated. We now expect that treatment will occur between Tuesday, August 31, 2021. Shoreline flyers will be posted on site no more than 48 hours in advance of the treatment. A second treatment is NOT anticipated.

Who is paying for this?

Due to the fact that the infestation of Eurasian watermilfoil was discovered early on, Lewis County Noxious Weed Control applied for an Early Infestation Aquatic Invasive Plant Management Grant from Washington State Department Ecology. With funds generated from the sale of boat trailer registration tabs, funding is set aside each year for the control of aquatic invasive species. With a 25% match in funds from Lewis County Noxious Weed Control, the Eurasian watermilfoil control work will be paid for by this Department of Ecology grant.

Mineral Lake, WA

Posted: August 11, 2021