Managing Weedgrowth in Your Tennessee Lake: Avoid Corporate Fraudsters

Managing Weedgrowth in Your Tennessee Lake: Avoid Corporate Fraudsters

There are many companies vying for the right to help you with your Tennessee lake. Several of those companies are corporately-owned; corporations tend to focus more on the bottom line, and less on what’s best for the landowner. Managing a pond is expensive; you owe it to yourself to hire someone who will put your interests first, as opposed to their bank account.

Duckweed is one of the most pernicious aquatic plants. It can go from a small presence around the perimeter of a pond, to covering the entire pond bank to bank, within a matter of weeks. Once it covers the entire surface of the pond, the pond is at risk of a fish kill: sunlight is blocked from penetrating into the water column, phytoplankton can no longer photosynthesize, the phytoplankton die, and the resultant decomposition of phytoplankton removes sufficient quantities of dissolved oxygen from the water to cause a fish kill. We have extensive experience with duckweed; it’s one of the first plants I ever treated, when I first started helping landowners with their ponds back in 1987. I learned very quickly that the chemicals commonly sold at your local farmer’s co-op or tractor supply as catch-all aquatic herbicides will not phase duckweed; I learned there are only a small handful of chemicals that will control this plant. We get several calls every year from landowners who have tried one of those chemicals on the duckweed growing on their ponds, at which point they realized that what the co-op sold them was useless against this particular plant.

It’s completely understandable for a co-op employee to not be an expert on aquatic herbicides; that’s not part of his job description. It’s not understandable for a degreed biologist who makes his or her living working on ponds to not be an expert.

We have a competitor that has two offices over a thousand miles apart; I don’t know for certain that they’re corporate-owned, but that fact alone makes it highly likely. They regularly advertise trying to acquire new clients in our service area; they brag on their website about how they’re managing a pond in a state south of us, a state that’s almost thousand miles from either of their offices. They claim to be experts in lake and pond management.

This same company just made a post on social media offering for sale their combination of three aquatic herbicides for the treatment of duckweed. Two of the chemicals are what the local co-op would sell you; the third would not even be recommended by the co-op, because it’s an algaecide that has zero effect on duckweed. There’s a photo of a pond covered by duckweed in the post; there’s no hint of filamentous algae anywhere on the pond pictured in the photo. Filamentous algae does sometimes occur with duckweed; by no means does it always do so; we have seen many ponds infested with duckweed that had no trace of filamentous algae.

The biggest isse we take with the post in question is simply the fact that it recommends a chemical that any knowledgeable biologist will tell you will control duckweed for all of about three weeks. As mentioned previously, this is literally the exact chemical that we hear about every year from multiple landowners, “This is what they sold me at the co-op,” and the next sentence is, “It didn’t work.”

The chemical in question is diquat. Diquat’s label does indeed claim it controls duckweed; it controls duckweed about as well as goats. I can honestly say I have never met a fisheries biologist with even a year of experience in the field who didn’t know that diquat is utterly useless on duckweed. As already noted, this is the chemical that co-ops and TSC’s sell for duckweed, because they only carry two or three aquatic herbicides and this is the only one that mentions duckweed on the label. But people who do this for a living are supposed to know what works and what doesn’t.

Even the content of the post beyond the chemical recommendation is wildly ignorant. Bear in mind, the social media post in question was made in August, when much of the U.S. was in a major heat wave; summertime is a great time to kill all of your fish with an improperly-performed weed treatment, because warm water holds less oxygen than cool water, most diseases of warmwater fish species are more active in water temperatures above 62 degrees Fahrenheit, and summertime is when weedgrowth is at its heaviest. When any plant is killed in a pond, as it dies, the decomposition process removes oxygen from the water; the larger the biomass of plants killed, the more oxygen removed. We always tell landowners not to treat more than 1/3 of a pond at a time for weeds even in the spring or fall, because we care about our customers and don’t want them to kill their fish; even government publications on pond management recommend not treating more than 1/4 to 1/3 of a pond at a time in order to minimize the likelihood of a kill.

So the social media post in question tells the landowner to treat half the pond, wait ten days and treat the other half. With a contact herbicide. Contact herbicides act quickly, meaning if you treat half the pond, all the duckweed contacted with the chemical will die at once, and you’ll have a massive fish kill. And then the duckweed will come back two to three weeks later because diquat doesn’t control the plant longer than that.

If, conversely, you use fluridone, which is a systemic herbicide and one of the two chemicals commonly used by biologists who actually are knowledgeable about aquatic plants, the plants will die more slowly, over four to six weeks’ time, drastically reducing the chances of a fish kill.

How long does fluridone control duckweed? I have never used it where it didn’t keep the pond completely clear of duckweed for at least a year; several times I have had it keep a pond duckweed-free for two years. It works just as well on watermeal.

Why would a company with two locations, and likely corporate-funded, recommend a chemical that will only keep a plant gone for two to three weeks? If it works briefly, but then the plant comes back, they have a reason to come to your pond again and charge you for another weed treatment.

This is the difference between hiring a company because they make a lot of social media posts and have multiple locations, or hiring a company that actually has decades of experience and a proven track record of success.