School has let out, summer is here, and with it comes new (old) challenges in the Extension office. Every summer, we receive a few questions about pond weeds and algae from individuals looking for treatment and management options of these problems.
There are several types of weeds that can be a nuisance in a pond – algae, floating, emergent, and submersed. Algae are technically not plants, but aquatic organisms that lack roots, stems, and leaves – they can be both microscopic (invisible to the naked eye) or macroscopic (visible), also called filamentous algae. Algae are very common in ponds. Floating weeds are aquatic plants that are not attached to the bottom of the pond, such as duckweed, bladderwort, and a few others. Floating weeds vary in size, and most of them have distinct leaves and roots that hang in the water. Next are emergent plants, which root along the shoreline, with the majority of the plant positioned out of the water. Think cattails, water lily, rushes, and other shoreline plants. Lastly are submerged weeds, which are plants that root in the bottom of the pond and do not rise above the surface of the water. There are many types of submerged weeds, including watermilfoil, coontail, and others.
It is important to note that some level of pond vegetation is beneficial to fish and other species, so our goal is not to completely eradicate all weeds in a pond. However, we do need to identify species that are problematic to the overall health of the ecosystem. For example, blue-green algae blooms produce toxins and odors that negatively impact human and animal health, while a duckweed infestation can cut off sunlight in the pond and reduce pond oxygen levels, killing fish and other desirable species. The first step in pond management for weeds is to identify what species are present and becoming an issue – this is best achieved by having your county agent visit the site, or by bringing samples of the different plants to the Extension office for us to examine.
Once the weeds are identified, we can begin developing a management plan. Some weeds may not require any kind of treatment, but if we do have some troublemakers, chemical control is typically our best option. Chemical control includes a variety of options including copper and other herbicides. It is important that all chemicals be used following labeled instructions – homeowners may find it best to hire a third party to properly treat the pond to ensure proper application of chemicals to treat a weed problem due to limitations of equipment and access. Physical removal of weeds, dying the pond, and other strategies are typically not very effective on large-scale weed infestations.
One issue with chemical control in ponds is that when we kill aquatic weeds, their decomposition process actually uses some of the oxygen in the pond. If we kill too many weeds at once, we starve fish and other species of oxygen, resulting in fish kills. Therefore, we recommend treating 1/3 of the pond at a time, and if possible, avoiding treatment entirely between June and August.
After the weed burden has been reduced using chemical control, general pond management strategies can be implemented. One of the biggest things to consider is the environment around the pond. When nutrients from animal manure, fish food, or fertilized pastures or lawns enter the pond (typically from runoff), there is usually an algae bloom in response, which can make weed problems even worse. Creating a barrier of vegetation around the pond’s shore and limiting the amount of nutrients around your pond is a great starting point to minimize weed growth. Sterile grass carp can help a little bit with controlling vegetation, but they are only able to eat young, immature weeds – if you have a large weed issue in your pond, stocking carp isn’t going to be sufficient control. Lastly, developing a pond liming, fertilization, and fish stocking program may be appropriate, depending on your goals.
Ponds can be tricky to manage, but we do have options to help! If you need help with a pond issue, please contact us via email (uge3181@uga.edu) or phone (706-359-3233).
