Aquatic Herbicides

Aquatic Herbicide Tips

Before using any aquatic weed killers in your pond or lake to control pondweeds or lake weeds, follow these tips to make sure you are using these products correctly and safely. 

• Identify: It is crucial to identify your pond weeds or lake weeds before you begin to treat. Some herbicides only work on certain plants.
• Check: Make sure the product you use is licensed for use around or in water. Using unapproved chemicals can be very dangerous to swimmers and aquatic life. 
• Follow rules: The instructions and warnings listed on all pesticide labels should be read as the law. Failure to follow these labels is illegal under state and federal laws. 
• Pay Attention: Many aquatic herbicides will break down quickly in water, but there is still usually a suggested wait period before fishing or swimming can take place.
• Dose properly: The dosing rates are usually listed right on the labels. It may involve some calculations, but it is important to follow the proper rates in order to keep you and your wildlife safe, as well as ensuring your product works well.
• Apply for optimal results: Timing in the year, temperature of the water, and placement of your application will all play into the success of your treatment. Timing is especially crucial, as weeds are usually perennials and you can apply them before they even begin to cause a problem. Do a bit of research or call your local extension office to find out the best time to apply aquatic herbicides for your specific weeds and area.

Types of Aquatic Vegetation

• Submerged vegetation: these are weeds that are rooted, but do not break the surface. This group can include Naiads, elodea, pondweeds, and Eurasian watermilfoil.
• Emerged vegetation: These plants are rooted but grow above the water. Cattails, bulrushes, and arrowhead fall into this category.
• Floating vegetation: These plants have leaves or flowers that float on the surface of the water and include waterlilies and watershed. 
• Algae: Algae is a healthy part of pond or lake environments. There are different types of algae, including filamentous and mat algae. See our algae page for more information on controlling algae.

Pros and Cons of Aquatic Vegetation

Before you go out and buy an arsenal of herbicides or rent an underwater weed harvester, remember that some vegetation is desired, and is a sign of a healthy aquatic ecosystem. Here is a list of positive and negative things that you should note before doing any aquatic weed management.

When Aquatic Weeds Help:

• Aquatic weeds, including algae, provide food for small fish, which in turn gives food to the bigger fish, providing an important piece of the food chain.
• Larger swaths of algae or flowering plants give shelter and provide habitats to a wide variety of animals, including fish and water foul.
• A healthy amount of aquatic plants provides abundant oxygen to aquatic life, keeping both plants and animals healthy and water cleaner.
• Rooted plants help to stabilize the pond or lakeshore and help filter pollution.
• Some aquatic plants provide an element of aesthetic beauty, like lily pads or cattails, which can add to your outdoor experience. 
• Remember, your goal is management, not eradication!

When Aquatic Weeds Hurt:

• An overabundance of vegetation can make recreational activities, like swimming, boating, or fishing, more difficult or unpleasant and detract from your enjoyment.
• Sometimes too many weeds cause oxygen depletion, which leads to fish kills and decomposition.
• Lots of floating or emergent vegetation can cause pockets of still water, creating breeding grounds for mosquitoes.
• Invasive aquatic weeds can quickly overtake native species and become a problem.
• When weeds overtake your pond or lake, it can make it very ugly, especially when algae or another small weed covers the entire surface.

For more infomation on how to apply aquatic herbicides, see our guide on How to Kill Algae and Weeds in Ponds and Lakes.

See also: Pond & Lake Supplies, Algaecide