Advantages and Limitations of Different Control Options
|Once you have evaluated these criteria relative to your goals, you have a number of management options. There are seven different general approaches: limiting nutrient inputs, physical removal, shading, chemical treatments, biological control agents, barley bales, and winter drawdown. The following is a brief summary of these management options, including a description of the technique and some of the advantages and disadvantages. This summary is not intended to be comprehensive.|
Nutrient Input Control:
Frequently the main factor allowing excessive aquatic plant growth is an overabundance of nutrients in surface water. Algae blooms are a good indicator of excess nutrients. These nutrients may enter from tributaries and from groundwater. Over time, these nutrients may also accumulate in the sediments within the pond.
Mgmt tool: Use best management practices (BMP's) for agriculture and use streamside buffers to reduce nutrient loading transported in tributary streams. Consider sewering to reduce inputs from septic systems and minimize the use of lawn fertilizers and pesticides. For small ponds, dig a small catchpool within the stream just upstream of the pond to trap sediments before they enter the pond.
Limitations: This strategy requires considerable involvement from the landowners and non-lakeshore community to in order to reduce nutrient loading. Limiting nutrient inflow in streams or groundwater will not address nutrients which have already accumulated in the lake sediments.
Physical Removal Methods:
Mgmt tool: Perhaps the simplest method is the manual removal of the plants using a scythe, rake, hoe or other tool. This technique works well for small patches of weeds, patches located in-between docks and other hard to get places, and in very large lakes or high flow lakes where chemical treatment is impractical. If a hoe is used, then the method is also fairly permanent because it allows the removal of roots so that the plant is totally removed. This technique can be inexpensive unless you have to pay diver wages. Hand removal also allows the selective removal of certain plant species, leaving others intact. A pool skimmer will work well for removing duckweed and true, floating plants..
Limitations: Cutting up some species allows them to disperse and get established elsewhere. This method is labor intensive and therefore not practical for large patches. It also works along shallow shorelines but is difficult where water depths are greater than 3 ft. In such areas, it may require personnel with diving abilities.
Mgmt tool: For larger lakes and large beds of aquatic plants, a mechanical harvester may be needed.
Limitations: Harvesters are expensive, specially designed boats which
generally require agency or government financing and operation. This technique
also results in large amounts of harvested weeds which require disposal. The
technique is not species-specific and also produces lots of small plant fragments.
For species such as Eurasian milfoil, these plant pieces are easily dispersed
and get established elsewhere in the lake. Harvesters do not remove roots so
regrowth and reharvesting is usually necessary within the same season.
Mgmt tool: The most permanent form of management is to remove the entire plant, including roots. This can be accomplished using underwater suction dredges for submersed plants or by using a backhoe along the shoreline for emergent species such as cattails.
Limitations: The equipment generally requires skilled operators and is expensive to operate.
Mgmt tool: Cattails (Typha spp.), giant reed grass (Phragmites) and Japanese knotweed (Polygonum cuspidatum) are particularly invasive emergent wetland species which dominate a pond shoreline. With persistence, these species can be gradually eliminated by frequent mowing (3 times per year) of the aboveground stems for several successive years. It is critical to cut off the aboveground plant material before it has time to do grow large enough to do significant photosynthesizing. The storage reserves in the below-ground rhizomes then will gradually be depleted.
Limitations: Large mowing equipment is needed. The necessary cutting is harder to do in high water years where the cattails will be in standing water.
Mgmt tool: Laying down dark burlap, plastic fabric, or geotextiles across the bottom in early summer prevents light from penetrating and therefore inhibits plants from growing. It is a useful technique for small patches and in-between docks.
Limitations: The cloth is hard to handle and secure; divers are frequently needed. Gas bubbles from the sediment can build up under the cloth and can cause it to float to the surface. Small holes need to be punched into the plastic at intervals of 2 feet. The cloths also tend to migrate down steep banks. Over time, sediment may accumulate on top of the cloth and new plants will establish themselves there.
Mgmt tool: There are several different chemical dyes available for controlling aquatic plant growth. They are usually inert, vegetable-based dyes, and work by reducing the penetration of plant-preferred light wavelengths to the plants. These are inexpensive and have no negative health impacts.
Limitations: Chemical shades are less useful in shallow pondshores (less than 50 cm deep and for plants, such as curly-leaf pondweed or duckweeds, which can get their foliage up to the surface to obtain light. Shades are also not useful for water bodies with a high flushing rate. Most chemical shades require a permit for their use.
Mgmt tool: A multitude of different herbicides are commercially available however they are almost all based on just seven different chemicals. They can be fairly species-specific and are easy to apply. Pellet forms are good for more localized use.
Limitations: Most herbicides require some delay before water can be used for swimming, fishing or drinking. Herbicides, especially in liquid form, do not work as well in systems with a high flushing rate. Rapid decomposition of the treated plants may result in algal blooms or "pea-soup" conditions within the lake. A few studies are linking herbicides to impacts on the health of amphibian populations. Permits are needed.
Chart on chemical herbicides.
Biological Control Agents:
Sterile grass carp
Mgmt tool: Sterile grass carp, introduced from Asia, consume large quantities of plants and are useful in the control of some species. Generally fish are stocked at 5 to 10 fish per acre of pond, with fish of 10-12" in length. The cost is relatively inexpensive, generally 15$ per fish. Only sterile grass carp are used in order to ensure that they don't escape and invade natural aquatic systems.
Limitations: The carp have plant preferences and if offered a range of plant options, they may not eat the targeted species. The carp convert the plant biomass into fish biomass and excrete large quantities of nutrients. These nutrients may result in a bloom of microscopic algae. Carp are carefully regulated by NYSDEC and a permit is needed for their release. Restocking is generally needed after 5 yrs.
Mgmt tool: Several aquatic insects are being shown to be useful in the control of E. milfoil and other invasive plant species. Densities of the insects have to be fairly high for control to occur.
Limitations: Research is not yet complete regarding the success of this method. Insects tend to be very host specific so accurate identification of the plants is critical. Once introduced, the insect populations follow natural cycles in density and their host plant will correspondingly vary in abundance from year to year. Availability of the insects is currently limited and costs can be high.
Mgmt tool: Consistent lowering of the water level to expose the shoreline each winter will result in killing the seeds, rhizomes and other reproductive propagules of many shoreline plant species.
Limitations: This method is not useful for floating plant species. It requires intensive water level management techniques, such as a dam or standpipe.
List of Plants for which this technique works: alligator week (Alternanthera philoxeroides), hydrilla (Hydrilla verticilata), cutgrass (Leersia oryzoides), bushy pondgrass (Najas flexilis), smartweed (Polygonum coccineum), leafy pondweek (Potamogeton epihydrous), and softstem bulrush (Scirpus validus).
Mgmt tool: Several studies have shown that barley straw will reduce growth of phytoplanton and filamentous algae in farm ponds. The method works best when the straw is loosely placed in net bags and floated on the surface, and when placed early in the season. The cost is minimal and there are no known health effects.
Limitations: The scientific basis for the effectiveness of the barley straw is not yet known. Therefore, the best methods of use are still uncertain.
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