Physical Control of Aquatic Plants

In addition to nutrient control strategies to reduce nuisance aquatic plant growth, there are a variety of physical, biological, and chemical strategies to reduce plant growth once it occurs. Keep in mind that these strategies will often have to be done each year until you address the underlying nutrients that are causing the plants to grow. Physical harvesting of aquatic plants and algae can be very effective, especially for small quantities of plants near the shorelines. It's time consuming and sometimes backbreaking work, but it can have a long-lasting effect if the plants are removed from the pond. That's because you're also removing the nutrients that are associated with the plants, making them unavailable for future plant growth. Just make sure that you dispose of the harvested aquatic plants far away from the pond to prevent nutrients from washing back into the pond. Many pond owners have developed innovative tools and techniques to accomplish aquatic plant harvesting. All of these methods involve some type of cutting, pulling, or netting. Be careful, though, because some submerged aquatic plants can reproduce through fragments left behind after harvesting, causing increased plant growth. Make sure you properly identify any plant and determine if it can spread by fragments before attempting to harvest aquatic plants. For larger ponds and lakes, companies with mechanized harvesters can be hired to remove aquatic plants and algae. These mechanized harvesters are expensive because of high maintenance costs and their limited availability. The most widely used type of equipment is called a plant harvester or weed cutter. Plant harvesters cut off the underwater rooted vegetation four to 5 ft below the water surface. As with hand removal of plants, mechanized removal offers the advantages of removing much of the nutrients associated with the aquatic vegetation, thus reducing future More and more pond owners are installing aation devices. There can be a number of benefits from airrating a pond, including reduced growth of some types of algae. The most efficient type of aation is diffuse aation, which involves introducing air bubbles at the bottom of the pond through air stones or hoses with small holes. The air bubbles rising from the diffusers on the bottom of the pond oxygenate the water and also push the oxygen pour water to the surface where it is reairrated through an exchange with the air. The resulting irration of the bottom pond water activates a number of complex processes that can help to control some algae by keeping phosphorus bound to the bottom sediments and unavailable for algae growth. Aation can also boost oxygen levels for fish where levels are low. The other type of pond arration involves surface irration through fountains. Fountains usually only irrate a shallow layer of water near the pond's surface, so they have little or no benefit to reduce phosphorus levels and control algae. The mechanical agitation of the pond's surface by the fountain will reduce the growth of some floating plants like water lily and duckweed, which prefer to grow in stagnant water. Another physical control strategy called draw down takes advantage of the fact that most aquatic plants and algae begin growing in shallow water near the pond edge. This involves partially draining the pond during the winter to expose shallow areas to freezing temperatures. When the pond sediments freeze, the roots of many aquatic plants are killed, causing reduced growth the following spring. Unfortunately, draw down can be difficult for pond owners to accomplish because they cannot easily draw the water level down and keep it lower for an extended time over the winter. It may also require a state permit depending on the size of the pond. A final physical control strategy is to dredge pond sediments to restore deeper water and limit sunlight reaching the pond bottom. Dredging can be an extremely effective and long-term solution to nuisance aquatic plant and algae problems, but it is also expensive, timeconuming, and damaging to the existing aquatic life. Dredging often requires a state permit, so consult your local Department of Environmental Protection office before