Aquatic noxious weeds — problems and solutions

By Chase Youngdahl
Reader Contributor

I have observed numerous abstracts and opinions regarding aquatic noxious weeds, including how they should be managed in our public waterbodies and the perceived ramifications of chemical management. I’m finding it necessary to provide a counterbalance to the dominant narrative. 

We have three submersed aquatic noxious weeds inventoried in Bonner County’s waterways — Eurasian watermilfoil, curlyleaf pondweed and flowering rush. “Noxious” is a regulatory term and is not interchangeable with the term “invasive.” While some noxious weeds are indeed invasive, not all invasive weeds are “noxious.” There are 70 non-native plants on Idaho’s noxious weed list (17 of them are found in aquatic environments), which is published in IDAPA Code 02.06.09 and subject to statutory management requirements (Idaho Statute — Title 22, Chapter 24). By contrast, there are hundreds, if not thousands, of nuisance and invasive weeds that are not subject to the same requirements. 

While herbicides carry a stigma, they are safe and appropriate management tools when used properly, as backed by peer-reviewed science. To boldly assert otherwise requires proof — not just anecdotal correlations. Nearly everyone uses chemical compounds in some form or another in everyday life without a second thought — whether taking prescription and/or over-the-counter drugs for a specific ailment or using conventional household cleaners. 

Most of us have chemicals in our mouths perpetually from resin-based composites used in restorative procedures for treating tooth decay. 

The point being: Chemical compounds are safe when responsibly used in the designed manner. 

In terms of aquatic noxious weed management, the primary stakeholders have a duty to utilize taxpayer resources in the most responsible fashion while upholding their statutory management responsibilities. Diver-assisted suction removal is well intended, and may be the appropriate tool for addressing sparse populations within potable water intake buffers, but is not fiscally realistic in terms of full-scope operations. 

When state and federal governments need to fund public safety, schools, highways/freeways, defense, etc., there’s only so much remaining for other statutory requirements, such as noxious weeds. I see no way that the Idaho Legislature would increase the Agriculture Department’s noxious weed budget 10- or 20-fold to manage all statewide aquatics mechanically. 

The agencies that are orchestrating chemical aquatic treatments are competent professionals who know how to engineer a proper operation. The herbicide labels serve as guiding documents — they are also legal documents — to execute safe treatments. 

Concerns regarding the decomposition of treated vegetation leading to fish mortality due to dissolved oxygen depletion are addressed on herbicide labels with specific application instructions on how to avoid this. The same goes for instructions on water use restriction intervals. 

Lake Pend Oreille has more than 100,000 acres of surface area, when you factor in Idaho’s portion of the river (more than twice the size of Washington, D.C.). Approximately a quarter of this area is in the littoral zone, where vegetation exists. When you’re talking about chemical aquatic noxious weed treatments totaling 100 acres, give or take, that’s more than reasonable in terms of limiting use to the bare minimum for meaningful management. 

Waiting to use herbicides as a last resort would mean that aquatic noxious weeds have expanded to such high levels that far more herbicide would need to be put in the water just to simply catch up. 

If your tolerance level for herbicides applied in our waters is zero, a possible solution is to submit a petition to the Idaho State Department of Agriculture to delist Eurasian watermilfoil, curlyleaf pondweed and flowering rush from the noxious weed rule. If the petition successfully opens negotiated rulemaking, be prepared to present a data-driven, merit-based case in which you will be competing with varying statewide interests. This is the same process by which weeds are added to the list.

Finally, when it comes to nuisance aquatic weeds — not noxious weeds — where waterfront homeowners hire professional aquatic applicators directly, it is in everyone’s best interest that the Idaho Department of Environmental Quality continues to allow these private operations through the Pesticide General Permit. If this option is removed from the waterfront homeowner’s toolbox, I have no doubt that some would attempt herbicide treatments themselves out of sheer exasperation. 

Such illegal DIY treatments would undoubtedly be carried out with disregard for label instructions, potentially leading to various forms of contamination that could be difficult or impossible to trace.

Let professionals be professionals. 

Chase Youngdahl is the director of the Bonner County Noxious Weeds Department.