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Aquatic Weed Control for Florida Ponds

Introduction

August is that time of year when our beautiful blue ponds tend to turn green.  Maintaining a healthy, weed and algae free pond or lake can be difficult in Florida when temperatures increase and we have plenty of sunshine.  Although it is good to have plants and algae in your pond that photosynthesize and release oxygen, too many of them can cause issues.  Thick algal mats or a proliferation of water hyacinth, for example, can cover the surface of a pond and block the sun from penetrating the water surface.  As a result, low oxygen environments can occur because other plants and algae in the pond, below the surface, are not able to photosynthesize.  Aquatic weeds can create further issues by clogging pumps, boat motors and wreaking havoc in our canals and other waterways.

What Causes Weeds/Algae to Proliferate in Ponds?

There are three main reasons that weeds and/or algae will proliferate in a pond; 1) warm temperatures, 2) sunlight and 3) availability of nutrients, especially nitrogen and phosphorus.  Weed outbreaks can also occur as a result of introducing plant propagules (seeds, tubers, stems, roots etc.) into a water body where they were not present before.

What Can I Do to Control Pond Weeds and Algae?

Preventative Measures

The old saying that “an ounce of prevention is worth a pound of cure” is very relative when considering aquatic weed control.  There are things that can be done to help address the three issues discussed above that lead to aquatic weed proliferation.  To help lower pond water temperatures, trees can be planted around water bodies to provide shade,  this vegetation will also help mitigate the amount of nitrogen and phosphorus flowing into the pond by taking it up via their root systems.  Shade from trees also helps limit the amount of sunlight available for photosynthesis, which in tern limits the amount of plants that can grow in the water.  Alternatively, pond dyes can be added and serve a similar function in reducing the photosynthetic capability of plants.  However, pond dyes need to be re-added to ponds depending on the amount of flow-through and some homeowners find the blue or green dyes unsightly.  The introduction of herbivorous fish can also help maintain plant and algae populations in ponds.  The two most common fish species used for controlling weeds in ponds are sterile carp and tilapia.  Stocking rates of herbivorous fish are dependent on the acre feet of your pond.  Acre feet can be calculated by taking the surface area of your pond (in acres) and multiplying it by the average depth of the pond.

Curative Measures

What are your options if, despite your best efforts to prevent weeds, you still end up with them?  Mechanical removal is very efficient but requires heavy labor and, sometimes, special equipment.  Chemical control options are also available.  Selecting and applying aquatic herbicides is a complicated endeavor and; unfortunately, there is no “silver bullet” for weed control.  The best product to use will vary depending on which weeds you are trying to control and where in the water column they reside.  Further resources are provided by UF/IFAS Extension and links to these articles can be found in the “Additional Resources” section below.

Additional Resources (Just Click on the Titles Below!)

Sterile Carp

Mechanical Control of Aquatic Weeds

Efficacy of Herbicide Active Ingredients Against Aquatic Weeds