By Jim Crawford, Field Specialist in Agricultural Engineering, University of Missouri Extension, Atchison County
The pond weed questions seem to be starting early this year. The early warm up coupled with the varying precipitation has led to some very early season pond issues. In most year, we do not see these issues until early June.
While some plants growing on or in your pond can be beneficial and attractive, if left unmanaged, some of Missouri’s aquatic plants can become nuisances in ponds. The first step is to identify the plant and verify if you need to and how to control it.
Generally, we group aquatic weeds as: growing around the edges such as water primrose and cattails, floating vascular plants like duckweed and watermeal, rooted floating plants like Chara and water lilies or as algae. Proper identification is the first and probably the most critical step in determining if a plant is a weed, if it is an issue and how to control it if necessary.
Plants such as cattails and water primrose can be a benefit for a pond depending on their location and their size. They provide habitat for fish and wildlife but can reach nuisance levels if neglected. They can become a real issue for fishing by making casting difficult and snaring fishing lines. Large, dense growth of primrose may provide too much protection for small bluegills, making it difficult for bass to obtain enough food for good growth.
Small amounts of duckweed and watermeal will not harm a good pond, but they quickly multiply and can reach a nuisance level in less than a month. They are important foods for wildlife, especially waterfowl. They provide habitat for animals such as frogs and turtles. However, if there are excessive nutrients in the water, dense duckweed growth can block out sunlight, shading out oxygen-producing plants below and upsetting a pond’s natural balance.
Floating rooted plants like Chara and water lilies also provide habitat for fish, insects and other aquatic wildlife such as snails, as well as adding aesthetic beauty to a pond. However, once established they can quickly reach a nuisance level if not controlled. Ideally, 10 to 20 percent of a pond’s bottom and surface should be covered in aquatic plants. More than this and they can shade the water, reducing oxygen levels as well as interfering with fishing activities.
Algae are simple aquatic plants common to virtually all Missouri waters. Unlike other plants, algae lack true stems, leaves, and roots. Algae are a basic component of a complex aquatic food web, converting the sun’s energy into a form useful to other aquatic life. During this process, algae also produce oxygen, which accounts for more than 50 percent of the oxygen in our atmosphere.
However, excessive blooms algae can cause taste and odor problems in drinking water and sometimes even fish kills, they can form dense growths that make fishing, swimming, and other recreational uses nearly impossible. Total coverage can restrict sunlight penetration and limit the production of oxygen and food items necessary for good fish growth.
Control for any of these nuisance aquatic weeds can be either cultural, mechanical or chemical and varies greatly depending on the species. The Missouri Department of Conservation has an excellent website that can help you identify potential weed issues as well as various control strategies – https://mdc.mo.gov/improve-your-property/habitat-management/pond-and-stream-management/ponds-plant-management/nuisance You can also reach out to your local county University of Missouri Extension Center for assistance with identifying any potential weed issue as well as possible control strategies if needed.