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Aquatic Weed Control
Intro |
Identifying Weeds |
Controlling Weeds |
List of Common Weeds |
Control Methods
- Biological Control
- Physical Control
- Chemical Control
- Mechanical Control
- Grass Carp
Chemical Control
Identifying a problem weed is the first step to controlling it. Herbicides are generally species specific, meaning they are effective only on certain plants. Herbicides are expensive, so it would not be wise to randomly select an aquatic-approved herbicide, since it may not be effective.
Chemical control requires using aquatic herbicides (and surfactants) that have met strict Environmental Protection Agency (EPA) standards for use in an aquatic environment. The herbicides are of low toxicity to fish and wildlife (and humans) when used according to guidelines, rates, and restrictions specified on the label for each herbicide. Some herbicides have limited livestock (cattle) restrictions before reentry into treated areas and limited irrigation use immediately following treatment.
Chemical control has its limitations. Applying herbicides may require specialized equipment and expertise. Some herbicides can be very expensive, and some may not provide prolonged weed control. Rooted aquatic plants usually develop in water that is too shallow or too clear. Even after treatment of the vegetation, the conditions may still be present for aquatic weed recolonization. Return of the same or another weed problem is often likely, requiring more applications of herbicides. It is important to eliminate the conditions that encourage the growth and spreading of aquatic plants.
Before using any chemical control, correctly identify the aquatic weed to be treated so you can select the most effective and economical herbicide. For assistance with aquatic weed identification, use the dichotomous plant key or thumbnail photographs or contact the Mississippi State University Extension Service (your county agent), the Natural Resources Conservation Service, or the Mississippi Department of Wildlife, Fisheries and Parks. In most cases, you can ship or mail a sample of your weed in a Ziploc® bag wrapped in a damp (but not wet!) paper towel to any one of these offices, and a biologist can make an accurate identification. You can also e-mail close-up, clear, detailed digital photos to these agencies for proper plant identification and recommendations.
You must know the surface area and/or volume of water in the pond, since the amount of herbicide to use is determined by either the surface area or water volume to be treated. Pond volume is determined by multiplying the surface acreage by the average depth of the pond, and is measured in acre-feet. Several important calculations are provided on the management calculations page. For additional assistance in calculating treatment levels and pond volumes, download the publication "Common Calculations Used in Fish Pond and Lake Management."
For effective aquatic weed control, you must select the appropriate herbicide and apply it properly. Some herbicides may be used directly from the container; others must be mixed with water, or with water plus a surfactant before being used. Use care when selecting a surfactant, because ionic surfactants (detergents) are not legal for aquatic use and may kill fish. Always follow label instructions and precautions when applying herbicides. Some may be applied by hand (low volume, spot spray), while others require the use of power sprayers (high volume, tank mix) or drip lines.
Time of Application
The time to apply herbicides is very important. Usually, treatments applied in the spring or early summer when the weeds are actively growing bring the best results. Herbicide applications in the late summer and fall are generally less effective for many species. Failure to control some problem aquatic plants can result in an increase in the affected area requiring treatment. Many of these plants make mature seeds by midsummer that sprout the following year.
In hot weather, be careful not to deplete oxygen by killing too many weeds at one time. Low dissolved oxygen levels can result from the natural decay of treated (killed) aquatic plants. Fish kills may result if the dissolved oxygen level becomes too low in your pond. It is seldom safe to treat more than half the pond at one time in the summer unless you are treating marginal aquatic weeds. A good rule to prevent oxygen depletion is to treat one-third of the pond; wait one week, and treat another one-third of the pond; wait a week, and treat the remaining one-third.
For many types of marginal (shoreline) vegetation problems, you may simply spot treat as needed to maintain good control. On older ponds and lakes where aquatic vegetation is well established, seek professional help to gain the control you need.
It is against Federal Law to use any chemical other than aquatic herbicides approved and registered by the EPA. Improper use of chemicals may result in serious environmental damage, fish kills, contaminated water supplies, and danger to human health. Diuron (Karmex®) is not approved for general aquatic use. Never apply it to recreational fishing ponds. It is also illegal to use Round-Up® in water, and Round-Up® in ponds may kill fish.