Chemical Control

Chemical control is the use of man made chemical compounds to manage the population of an invasive aquatic plant. These compounds are known as aquatic herbicides. In order to come to market all pesticides, including aquatic herbicides, must go through rigorous testing and research by the manufacturer before being approved for use by the Environmental Protection Agency. Pesticides are packaged and sold to consumers with legally binding instructions called a pesticide label, and must be applied by or under the supervision of a certified applicator, in Maine they must be certified by the Maine Pesticide Control Board. Failure to follow the directions on the label or to apply pesticides without certification is a federal offense. In Maine the use of aquatic herbicides is tightly regulated by the Department of Environmental Protection. Permitting is required. So far there has been limited use of aquatic herbicides, reserved for the direst of situations. Pickerel pond in Limerick has been treated for hydrilla with a mixed degree of success.

There are four major classes of aquatic herbicides: contact, systemic, selective and non-selective. Contact herbicides kill the part of the plant that they come into contact with, meaning that they may or may not damage the interior tissue. They are fast acting but fairly non-selective. The effect of use on woody plants is generally defoliation and new growth may occur. Use on herbaceous plants, which includes most aquatic plants, generally results in a more complete kill of annuals, but re-growth can occur on plant parts not targeted. If the shoot is contacted, the roots may remain alive and retain the ability to grow and reproduce. Systemic herbicides cause death of the entire plant, as they are absorbed and move through tissues. Their effect takes place at a slower rate, but they are generally more effective than contact herbicides. Contact and systemic herbicides can then be classified with the following selectivity: Selective herbicides only affect specific the plants they come in contact with, whereas non-selective herbicides affect all plants in contact. Some Pesticides also contain an adjuvant, nontoxic compounds in a pesticide mixture that increase the effects of the toxic compounds. New Hampshire has recently used herbicides to control variable leaf milfoil. To learn more of their efforts visit http://www.des.state.nh.us/factsheets/bb/bb-52.pdf

A licensed applicator treats a lake with aquatic herbicides in Florida

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