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Chemical Treatment and Harvesting to Control Aquatic Plants
Each year Professional Lake Management, following the guidelines stipulated on a permit issued by the Department Of
Environmental Quality, chemically treats parts of Lake Mitchell based on recommendations resulting from boat
surveys conducted on Lake Mitchell by Progressive Engineering AE limnologists. Members of the Lake Mitchell
Improvement Board, and occasionally, Lake Mitchell property owners, accompany Progressive Engineering staff on
these boat surveys. The boat surveys occur in early June and the chemical treatment follows about ten days later.
Follow-up surveys and treatment may occur in July.
The following three products are used for chemical treatment on Lake Mitchell:
1. 2-4-D, which kills milfoil, is a systemic chemical meaning that it kills the entire plant, roots and all.
Because of the presence of shallow wells this chemical must be used no closer than 250 feet from the shore.
2. Trichlopyr, with a brand name of Renovate, is also a systemic chemical, and is used near shorelines. While it
may used within 24 hours to water established lawns, it shouldn’t be used on plants until the treated area has been
tested.
3. Reward is another chemical that does not have a well setback restriction, but it is a contact herbicide, rather
than a systemic one. This means it kills only the portion of the plant that it comes in contact with. It is
commonly used near shorelines.
All chemicals have a 24-hour restriction on swimming.
Chemical Treatment Boat
Weed Harvesting
Because milfoil spreads by fragmentation, chemical treatment is the primary means of controlling that plant. Once
the plant has been killed by chemicals, then harvesters can be used on the dead milfoil and other nuisance
vegetation. Harvesting is used where native plants are so dense as to cause problems for boating. This means that a
lane will be cut so people can get their boats from their docks to open water.
Because harvesters are too big to maneuver between docks and need 18” to 2 ‘of water to operate, not all weeds will
be cut. In addition DEQ regulations forbid the cutting blades from digging into the bottom muck as that, according
to the DEQ, would be dredging. The DEQ also stipulates that at least 20% to 40% of the littoral zone (meaning along
the shore) be left vegetated to provide habitat for fish.
Without harvesters to cut and remove plants, shallow areas would be rendered unusable for recreation. However
harvesting does not eliminate weeds permanently; during peak growing season, mature plants may appear in harvested
areas within a few weeks after a cutting.
Harvester
As harvesters cut weeds they are fed onto a conveyer belt that carries them to a
collection bin. When the bin’s capacity is reached, the harvester returns to shore and off loads the weeds onto a
dump truck which carries the weeds to an area farmer who uses the weeds for mulch. Every effort is made to insure
that weeds cut by the harvester do not escape and float to other parts of the lake. Most floating vegetation has
been cut by motor props, dropped by anglers, and is the result of the natural or chemically induced die-off of
plants.
Harvesting usually occurs during the last week of June. Property owners are encouraged
to visit Big, Little, and the Franke Coves to observe the harvesting.
A native plant, naiad, grows in the deeper waters of the main lake. Its presence, as
floating mats of weeds on top of the water, prompted the establishment of the Lake Mitchell Improvement Board in
1989. It is an annual plant, which dies and breaks off in late summer and floats to shore.
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