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When and How to Apply Aquatic Herbicides to Lakes?

What Are Aquatic Herbicides?

Aquatic herbicides are chemicals designed to control or eliminate overgrown, invasive, or otherwise unwanted aquatic plants and algae. Excessive aquatic plant growth can put a lot of pressure on a lake’s ecosystem. This can lead to fish kills and other problems, so it is important to monitor and manage the plants in your waterbody. Aquatic herbicides are an effective management tool to consider.

Generally speaking, there are two kinds of aquatic herbicides: contact herbicides and systemic herbicides. Contact herbicides are exactly what they sound like; they kill the parts of the plants that they make contact with. Systemic herbicides, on the other hand, have to be absorbed by plants in order to be effective. Once absorbed, they can travel through the plants and kill the roots and reproductive components. Additionally, herbicides can be categorized as selective or non-selective. Selective herbicides kill specific, targeted plants whereas non-selective herbicides are non-discerning and will kill many plants.

It is important to note that in order to use aquatic herbicides, they must be registered with the Environmental Protection Agency (EPA) and respective state Departments of Agriculture. Additionally, many states require you to obtain a permit in order to use herbicides in water.

You may be considering using aquatic herbicides but have some reservations or questions. You may be wondering, are aquatic herbicides safe? When should I consider using herbicides in my lake? How do I actually apply aquatic herbicides? Read below for some answers and advice. 

Are Aquatic Herbicides Safe?

Aquatic herbicides are safe and effective for lake weed control. In order to be used, aquatic herbicides need to be registered and approved by the Environmental Protection Agency (EPA). This is a long and difficult process requiring years of research. The EPA will not register a herbicide for aquatic use if there is even a small chance that it could cause significant damage to the environment, wildlife, or human health. Of course, it is still important to read the label of the product closely, apply the product in accordance with the label guidelines, and be aware of any restrictions detailed on the label. 

When Should I Use Aquatic Herbicides for Lake Weed Control?

As mentioned above, aquatic herbicides are a great option for controlling lake weeds when growth becomes excessive. To use herbicides effectively for lake weed control, they must be applied when the target weeds are present. For best results, treatments should be conducted when plant growth is nearing or at the surface of the water.

Timing your aquatic herbicide application depends on:

  • the herbicide you are using
  • the plant(s) you are targeting
  • local regulations.

For example, some herbicides work best when the water temperatures are at a certain level. Lake Restoration’s product, Dibrox®, for instance, is most effective when applied to water that has reached or exceeded approximately 50°F, meaning that it would make most sense to use it in the spring and summer months. It is also important to understand cycles of weed growth in the treatment area when determining treatment frequency and timing.  Some weeds, such as curly-leaf pondweed, grow early in the season, while others, like coontail, flourish in the summer months. So, you will want to time your herbicide use accordingly. Additionally, local regulations may dictate when and how frequently you can apply herbicides. Minnesota, for example, only issues permits for 1-2 submerged weed herbicide treatments per year.

It is also important to consider that it generally takes 2-3 weeks after the application to see the full results of the treatment. It can be useful to time aquatic herbicide applications to maximize use and enjoyment of the water.

How to Apply Aquatic Herbicides to Lakes

There are multiple steps to follow when applying aquatic herbicides, and most of them are before the actual application. Work through these steps to understand the specifics of your water and the plants in it to develop an effective treatment plan:

  • Calculate your treatment area
    • Determine how many feet of shoreline you want to treat, as well as how many feet out in to the lake you would like to treat
    • Determine the average depth of water in this target area
  • Identify the weeds you want to control
    • This allows you to choose the best herbicide. One resource you can use to do this is Lake Restoration’s Aquatic Plant ID tool.
  • Choose a herbicide and read the product label
    • Read the first aid/safety recommendations, precautions, and environmental hazards. Remember that these statements are precautionary.
    • Focus your reading on the “Directions for Aquatic Use” section.
    • Double check that the weeds you are targeting are on the list of weeds controlled by the product. If there are asterisks or notes for your target species, be sure to read them thoroughly as they are there to help you best control the plants.
  • Determine how much product to use to treat your target area
  • Perform Aquatic Herbicide application
    • Plan for a sunny and calm morning for application. When the day comes, have your personal protection equipment (PPE) and application equipment ready.
    • [Liquid Herbicides] like Lake Restoration’s Dibrox®, Aquathol® K, and Flumigard® SC: for many herbicides, the application equipment will include a sprayer, measuring device, and water source.
    • [Granular Herbicides] such as Hydrothol®, Navigate or Aquathol® Super K: use a broadcast spreader to get even coverage of the product. The herbicide label will offer guidelines on how many pounds to use given your target area and depth.
  • “Hurry up and wait” for full results of treatment
    • Generally takes around 2-3 weeks to see full results

Managing lake weeds is an ongoing commitment and can require a lot of work on your part but using aquatic herbicides can help lighten the load. Additionally, MuckMaid® pellets can dissolve the muck on your lakeshore, revealing more sand and reducing the thickness of weeds that grow there. Check out Lake Restoration’s Dock and Swim Area Products! Consider adding aquatic herbicides to your management plan so you can get the most out of your lake shore.