Weed Control

Guide to Herbicide Selection and Use

Guide to Herbicide Selection and Use

For effective aquatic weed control, you must select the appropriate herbicide and apply it properly. Some herbicides may be used directly from the container; others must be mixed with water or with water plus a surfactant before being used. Use care when selecting a surfactant, because ionic surfactants (detergents) are not legal for aquatic use and may kill fish. Always follow label instructions and precautions when applying herbicides.

The time to apply herbicides is very important. Usually, treatments applied in the spring or early summer when the weeds are actively growing bring the best results. Herbicide applications in the late summer and fall are generally less effective for many species. Failure to control some problem aquatic plants can result in an increase in the affected area requiring treatment. Many of these plants make mature seeds by midsummer that sprout the following year.

In hot weather, be careful not to deplete oxygen by killing too many weeds at one time. Low dissolved oxygen levels can result from the natural decay of treated (killed) aquatic plants. Fish kills may result if the dissolved oxygen level becomes too low in your pond. It is seldom safe to treat more than half the pond at one time in the summer unless you are treating marginal aquatic weeds.

Read on for a list of approved herbicides and the common plant species for which they are effective, herbicide use restrictions, and useful application calculations and conversion factors.