07/25/2025
In response to a previous post on this MLIA FB Page:
Thank you for reaching out with your concerns regarding the use of Diquat to manage invasive aquatic plants in Mona Lake. Diquat is an herbicide that is approved by the U.S. Environmental Protection Agency (EPA) for use in aquatic environments under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Its use is steered by extensive environmental and toxicological testing to ensure safety for aquatic organisms, wildlife, human health, and drinking water sources when applied in accordance with label directions. Once approved for use, herbicides get routinely reviewed every ~5 years.
When reviewing publications on the potential dangers of Diquat, an important item to note is that the application rates used in real-world lake treatments are significantly lower than the concentrations tested in laboratory or regulatory studies. These studies often rely on high-end exposure situations to establish safety margins and worst-case benchmarks.
In contrast:
Lake applications use the minimum effective application rate to control target plants (Eurasian watermilfoil & Curlyleaf pondw**d). Real-world use is often 10 to 100 times lower than levels shown to cause any adverse effects in laboratory settings.
Diquat binds rapidly to organic matter and sediments once applied, which further limits its mobility and bioavailability in the water column.
There is no swimming restriction on the herbicide label for Diquat. This restriction is put in place by the state to ensure residents are out of the water at the time when our boats are coming in close to shore, around docks.
Most aquatic herbicides are mixed with water and evenly applied over the surface of the water. Dilution soon effects the concentration of an herbicide in the water. For example, Diquat when applied at two gallons per surface acre (max allowed) would require a 150-pound person to consume 3,750-7,500 gallons of treated water immediately after application to ingest enough active ingredients (diquat dibromide) to achieve a lethal dose concentration 50 percent of the time.
In addition, applications are conducted under strict guidelines outlined by MI-EGLE, by licensed (PLM) professionals who are trained to follow best practices for aquatic pesticide use. Numerous studies and decades of practical use across the U.S. have shown that, when used according to the label, Diquat is an effective part of an integrated aquatic plant management program.
Also, I saw a comment about posting of the signs. We typically use one sign for the entire lake, even though some areas may not be receiving all the herbicides listed. From our experience, this cuts down drastically on confusion about who has what restrictions.
Thank you,
Jaimee Desjardins, Environmental Scientist
Senior Regional Manager - Alto
PLM Lake & Land Management Corp.
