Hearing people talk about "invasive" and "non-native" plant species is a common occurrence in the pond management world. These plants can cause major issues for land owners who prefer to use their ponds for recreation purposes, such as fishing or swimming, and also can severely impact the pond ecosystem as a whole. Invasive species are any living thing not native to an area, which tend to spread excessively to the point of causing harm to the environment. These plants, because they have been introduced outside of their native region, lack a natural biological control.
There will be no natural predator or competitor to help control the population, so these species thrive to the highest of their ability. From a biologist's perspective, these plants can cause major issues. Aquatic invasive species (AIS) often spread so aggressively that they choke out sunlight and nutrients from other native species, forming what is known as a monoculture. Monocultures reduce biodiversity and can completely change the entire ecosystem of the pond, often for the worse.
Often, pond owners are more concerned with recreational use of their ponds. Who wants to spend time and energy maintaining a pond they can't swim in, or teach kids how to fish in? The issue with aquatic invasive species, specifically plants, is that if they are not properly managed, they will take over a large portion of the water body. We've all seen ponds totally filled with aquatic plants that people wouldn't dare try to take a row boat on, let alone swim in. So, what are some different kinds of aquatic invasive plants and how can we avoid letting them take over our ponds?
Water Chestnut is a plant native to Eurasia, with distinguishing triangular leaves that float on the surface of the water. The plant can be rooted in the substrate in shallow waters, but can also be found growing in open water. The fruits grow in a hard, black shell with four spines. These spines are sharp and can easily puncture a foot when stepped on. They are not something that you want littering the shoreline, especially if swimming is an important part of recreation. This plant can also be harmful to the biotic community within a body of water. They reproduce quickly and form dense mats of leaves floating on the surface. The dense mats make it difficult to navigate boats or kayaks and make swimming very unpleasant. They also block sunlight from other plant species which serve as food and habitat sources for other organisms such as fish and invertebrates.
Once Water Chestnut gains a foothold in a waterbody, the spread is inevitable. Each spiny fruit holds several seeds with the possibility of becoming new plants. Seeds within the fruits will also stay viable for years after the seed is dropped. Not only do these plants reproduce rapidly from seeds, they will also form new plants from fragmented pieces transplanted to new locations. Prevention is key in avoiding the takeover of Water Chestnut in your pond. Make sure to clean any equipment that has been in other water bodies before putting it into your pond. That is essential in avoiding the spread of any invasive species. If, by chance, Water Chestnut does enter your pond, early detection can be a huge help. With fewer plants, it will be easier to eradicate. Hand-pulling this plant when it first arises can be successful in smaller patches, and will help prevent spread and take-over of your pond. For larger areas where Water Chestnut has taken over, herbicides can be successfully used, depending on the laws in each state. Although eradication methods could seem successful year- by-year, the pond should continue to be moni-tored, as the seeds will stay viable in sediment for several years.
Another common AIS in lakes and ponds is Eurasian Water-Milfoil. This is a rooted, submerged plant that can grow very tall and dense. This species will reproduce and form a dense mat just below the surface of the water. Very similar to Water Chestnut, milfoil doesn't allow sunlight to reach other plants and chokes out other important native species. Milfoil does reproduce via seeds; however, its more successful form of reproduction comes from segmentation and fragmentation. Pieces of the plant break off, settle in the substrate, and form new roots. The plants will die off in the winter, but the root systems survive until spring and grow again.
Control of Eurasian Water-Milfoil is similar to that of Water Chestnut. Plants can be removed by hand, or treated with approved aquatic herbicides. However, hand removal of this plant can be very difficult for success, especially in thick density areas. All of the root system has to be removed and you have to be very careful not to cause fragmentation. Even very small pieces of the plant have the ability to re-root themselves and grow, so if it is not all removed, it will quickly grow back. Herbicides should be used in the spring when the plants first start growing to avoid any potential harm to native plant species. Biological controls can also be implemented for Eurasian Water-Milfoil. An aquatic weevil (Euhrychiopsis lecontei) can be stocked into lakes. The weevil prefers Eurasian Water-Milfoil as its host over other native species, and it helps to control the spread of the plant. Some states allow the use of triploid grass carp, which prefer this species of plants as well.
On a bit of a different note, there are also emergent plants that can negatively impact the environment of your pond. Giant Reed, also known as Phragmites can grow in just about any type of wetland. If it becomes established on the edge of your pond, it will reproduce rapidly and take over the shoreline. This creates issues for pond owners because the plant can grow up to 15 feet tall, blocking the view and limiting access points. This plant reproduces from seeds but more commonly by sprouting off of underground stems, also known as rhizomes. The reed does not provide a benefit to wetland species because the clusters are too dense to provide habitat, and it doesn't supply a food source.
Mechanical removal, chemical treatments, and prescribed burning are all methods that can be used to eradicate Giant Reed from your pond. Giant Reed is so resilient that using multiple methods of removal is often necessary. Applying a chemical treatment and allowing it to do its job for a couple of weeks is the best way to start the process. After the chemical treatment has had time to work, physical removal should be considered. Physical removal includes mowing, weed whacking, and in serious situations, prescribed burning or excavating. As with all other aquatic invasive species, prevention is key. Always make sure your boats and equipment are clean and dry before bringing them anywhere near your pond, and remember to keep on top of these species if they are ever established in your pond to ensure that they don't grow back in later years.
To avoid future headaches, always be mindful of species that may be coming in contact with your gear. If you use a boat in a water body that is known to have aquatic invasives, be sure to drain all water from the boat and allow it to dry for at least a few days before bringing it back to your personal pond. Being aware of what you are bringing into your pond could save you the trouble, as well as a lot of time and money, of having to deal with aquatic invasive species.
Reprinted with permission from Pond Boss Magazine