Management Technique: Mechanical Harvesting

Milfoil Management Technique Information Sheet These information sheets are intended to be objective summaries of what we know (and don’t know) about each management technique. Management Technique: Mechanical Harvesting Description: Harvesting is a way to mechanically remove any type of pond or lake weeds, including milfoil, in order to provide open areas of water for recreational activities and navigation. Harvesting removes vegetation from 2 to 7 feet below the surface. The harvester gathers the cut plants by a conveyor that leads to a rear hopper (storage area), which also has a conveyor belt and allows plants to be off loaded onto shore. Harvesters come with a variety of options, including cutting width and plant storage capacity. The WLPOA unit is a mid-size model. Effectiveness: Harvesting is a temporary solution to dense areas of vegetation. Depending on machine size and operator ability, 0.2-0.6 acres per hour can be harvested. This procedure can be effective for as little as a few weeks up to half of a season. It is analogous to mowing a lawn, but like lawn mowing, it can influence which plants grow best when applied over an extended period of years. Invasive species can be controlled but are not eliminated unless they depend on seed production and harvesting prevents seeds from being produced. Milfoil can produce seeds, but depends mainly on vegetative propagation. Fragments generated by harvesting are not all captured and can actually encourage the spread of milfoil. Costs: Commercial harvest costs vary depending on the target plant(s), the density of growth, travel distance for disposal of harvested plants and the number of obstructions present. The harvesting cost per acre usually ranges from $350 to $550, including trucking and disposal. An exception to this range is very dense growths where costs can range from $1000 to $1500 per acre. When a lake association owns its own harvesting equipment and has substantial experience with operation and maintenance, costs may be lower. The purchase price of WLPOA’s harvester was $90,000 in 2011. Yearly maintenance and operating costs vary depending on frequency of use. Labor costs in 2011 were $2,300 and in 2012 $3,000. These numbers include operating the harvester and recovering plant and other debris on or near shore. History of Use at Woodridge Lake: Harvesting has been used each summer by the WLPOA for pond weed, especially in the north cove, to facilitate easier boat navigation. Harvesting has never intentionally been used for milfoil harvesting due to the risk of plant fragmentation, which can spread the weed to other areas of the lake. Our most recent lake vegetation survey from Aquatic Control Technology shows dense milfoil growth in the north cove which ACT has targeted as a number one priority for management. Use at other lakes in CT: Indian Lake (Sharon, CT), Bantam Lake (Morris, CT), Lake Buel (Monterey, MA) Buel does not have drawdown capacity and herbicide treatments were not preferred by area residents. A harvester was purchased and is used almost continuously in the summer to keep milfoil patches in check over about 80 acres of infested area. Over time, some shift in favor of macroalgae has been observed in some areas, but milfoil remains the dominant plant in the lake. Permitting: State of Connecticut does not require permitting for mechanical harvesting. Considerations: General plant mapping and knowledge of sensitive areas (already done by WLPOA) is important prior to harvesting. ACT has provided the WLPOA with detailed mapping of milfoil densities and prioritized treatment areas. As stated earlier, harvesting is not preferred for milfoil control, but can be used to keep navigation lanes open. The number of acres to be treated will also determine harvesting feasibility. Other variables such as water depth, prevailing winds, ability to off load plant material and environmentally sensitive areas all need consideration in any harvesting plan. Summary: While some view harvesting as an excellent non-chemical method of milfoil, recent data from ACT on milfoil density seems to prove otherwise. Merely mowing the plants and allowing the escape of cuttings to grow in other parts of the lake is not acceptable. On the other hand, harvesting may release nutrients from the biomass, but various studies have demonstrated this to be a minor influence on the nutrient budget of lakes. Because only the top part of the plant is removed, the rest of the plant remains for habitat and sediment stabilization. Harvesters are very large machines and can occasionally leak hydraulic fluid or fuel. Operation of these machines need a comprehensive spill plan with containment equipment available at all times. During shallow water operation the propulsion system may alter sediment in addition to removing small fish and other aquatic organisms. Although harvesting is not a good option for milfoil management, it does have a place in managing other areas of vegetation in the lake. .

Load more