Aquatic Herbicide Control Methods
Aquatic plant management: aquatic herbicide control methods
Aquatic plants are an important part of a healthy lake. They provide food and home for fish and wildlife, stabilize soil, and prevent shoreline erosion. Some aquatic weeds are considered invasive and may cause problems. At other times, native aquatic plants may become a nuisance. If a lake management service provider says treatment of lake plants is needed (see “Management plans” page), lake stakeholders have options for aquatic weed control. These include herbicides, physical/mechanical, and biological methods (the latter two have separate pages).
What are aquatic herbicides?
Lake weed killers, or aquatic herbicides, are chemicals made to damage or kill lake plants. Examples of lake herbicides used for aquatic weeds are 2,4-D, triclopyr, diquat, and fluridone (they have trade names too). The use of a newly developed aquatic herbicide, florpyrauxifen-benzyl (trade name, procellacor) is increasing, as initial results show it is effective on invasive aquatic plants and better for native aquatic plants and wildlife.
Aquatic herbicides vary in several ways. They work through contact (herbicide injures the plant tissue it contacts) or systemic (herbicide is absorbed through leaves, stems or roots and moved through the plant). Contact herbicides can appear more effective because plant damage occurs quickly (hours to days) while systemic herbicides take longer (days to weeks). Which type of pond weed killer is most appropriate depends on factors like water use, native pond weeds, the invasive species identity, and lake conditions (e.g., water movement, depth). A lake management service provider (see “Management plans” fact sheet) can help decide this.
Benefits and drawbacks of herbicides
Aquatic herbicides and pond dye for aquatic plant control may offer benefits to nature and people if applied properly, following a lake management plan. By reducing invasive aquatic weeds, they can ease recreation and aid habitat for native lake plants and animals. They are relatively easy to apply (as compared to some mechanical/physical methods) and often result in a fast reduction of invasive water plants. Yet, they have drawbacks that aren’t always known to stakeholders.
First, they can have limited effectiveness. This can result from using the wrong herbicide for the situation (it is not effective for that lake plant or the lake conditions). In addition, many kinds of lake weed killer only ‘knock down’ aquatic weeds for several weeks. Many invasive aquatic plants regrow within the same season, or next season, leading to repeated herbicide treatment with little long-term improvement. This is most true for partial lake treatments (whole lake herbicide applications may last longer).
Second, most aquatic herbicides have some negative impacts on native lake plants, invertebrates, fish, reptiles, amphibians or birds (these are called ‘non-target impacts’). In a Wisconsin study, exposure to 2,4-D at normal amounts impacted larval survival or development of northern pike, largemouth bass, walleye and yellow perch. A second Wisconsin study compared the natural effects of Eurasian watermilfoil with the effects of lake-wide herbicide treatments (2,4-D) used for milfoil control; they found that lake-wide herbicide treatments aimed at controlling Eurasian watermilfoil had more negative effects on beneficial native aquatic plants than did Eurasian water milfoil itself. While this study only looked at some herbicide/plant combinations, it shows the importance of comparing impacts of lake plant management with the impacts of the lake weed itself. Note that many lake weed killer applications only result in short-term control (e.g., 2,4-D on Eurasian milfoil). The short- and long-term non-target impacts of aquatic herbicides on wildlife should be considered.
How to conduct an aquatic herbicide treatment?
In many states herbicide can not be applied to water without a permit from the state natural resource agency. Given the complexity when selecting and applying a pond weed killer (which, when, where, how to apply the herbicide), stakeholders should work with a lake management service provider and their state natural resource agency to make a treatment plan. The service provider assists with determining the optimal approach for your lake (see “Management plans” page). The state’s natural resource agency is also a good resource for advice on the management of nuisance and invasive aquatic weeds. While small-scale applications may be done by stakeholders, due to equipment, scale, and safety, it is more common to hire a professional treatment applicator following an aquatic plant management plan. Selection of a treatment applicator can be simple. The lake management service provider will recommend which treatments to use, and an internet search for that method and your location within the state should yield results. From there, a comparison of estimates and referrals will help narrow down the choice. For the applicator, a degree is not needed but knowledge of water plants and a license from the USDA and state permitting agency (e.g., Wisconsin DNR) is needed for application. Aquatic herbicide treatment needs permits at the state level and notice to lake property owners near the treatment area.
The cost of aquatic herbicide application depends on which herbicide is used, if pond dye is used, the area treated, and the number of treatments.