Last Updated: May 2005
Rotovation is a technique that was originally developed by the British Columbia Ministry of the Environment to combat noxious weeds in their lake and river systems. Chemical control techniques were not possible because of the lack of registered compounds in Canada, and the Ministry was looking for mechanical methods that would lengthen the effective control period. When properly applied his technology is very effective in meeting those criteria.
Operators need to understand that some plants normally build up an extensive mass of material in the soil that can be expected to generate new plants. Rotovation typically provides much longer control of weeds than conventional weed-harvesting operations by disrupting tubers, roots and other plant material in the sediments.
Description
Rotovators are basically large underwater rototillers. The knives penetrate the soil, till it, and release the root crowns and other plant tissue. The tiller is mounted on an arm similar to a backhoe and can be lowered into the water and held against the sediments. Rotovators can reach bottom sediments to depths of 20 feet.
The operator tills the vegetation in target areas using a cross-hatch pattern. A number of lines are tilled in one direction then the equipment repositions itself and cuts a number of tillage lines across the original lines at a 90-degree angle. Intensive tilling results in removal of the root crowns of the plant and/or the below-sediment structures. It will also cut and disturb any crowns that are not removed. This provides long-term mechanical control of this weed.
Operational Considerations
The primary operational consideration is selecting the proper rotovation equipment. Tillers should be well constructed to prevent damage when they encounter underwater obstacles. To make them effective they should be flexible and mounted on a vessel that can deliver both power and mobility.
The operator has control over the effectiveness of this process. Long-term control is dependent on adequate removal or disruption of the subsurface structures of the plant. The operator has to track the progress of the machine and ensure complete coverage of the target area. Overlap is critical to clearing an area.
Since the tiller is disrupting bottom sediments, there is a need to avoid contaminated sediments . Studies done on the turbidity produced by rotovation have indicated that baseline conditions are reached fairly rapidly once the tiller has passed. Tilling sediments that are contaminated could possibly release toxins to the water column. If there is any potential of contaminated sediments in the area, further investigation should be performed to determine potential impacts from this type of treatment.
Areas that have large numbers of obstructions, such as trees or stumps in impounded reservoirs can have an impact on rotovation operations. The tiller cannot effectively operate in these areas and other methods should be considered.
Tilling during fall, winter, and spring, when limited biomass is present in the water column, can speed the operation dramatically. It will also reduce the impact of the operation on other water uses, such as swimming or boating that might take place in the summer months in targeted areas. In addition, rotovation during these optimal time periods will reduce the amount of vegetation that is severed from the lake bottom.
There may be a need to collect the plant material that is tilled from the bottom. If operations are releasing large amounts of plant material, harvesting equipment should be on hand to collect this material and transport it to shore for disposal.
Rotovation should not be used in areas where plants are just invading, unless there are limited options. Like harvesting, cutting the plants and failing to collect all fragments can lead to the accelerated spread of the weed within the water body. This technique is more appropriate when the operator is interested in long-term mechanical control in established plant beds.
Expected Results
Rotovation provides dramatically longer periods of control of invasive plants than does harvesting. Exotic weeds pose a major threat to an infested water body and all surrounding waters. When the plants are well distributed mechanical control methods should be considered for use as maintenance tools or where there are limited options.
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