County Gardeners Extension Express
Pondweeds
Whether it be in the lawn, garden, or pond, weeds can be a consistent problem. Today I am going to talk about a varied group of plants called pondweeds, which (as you might guess) can be found in a pond.
Pondweeds are a group of rooted plants with alter- native leaves. The leaves can be totally submerged or float on the surface of the water. The flowers and fruits are normally green to brown, small, and close together in oblong or ball-like spikes. Submersed leaves are thinner compared to floating leaves, are somewhat translucent, and positioned alternately along the stem. Floating leaves are more oval shaped than submersed leaves, leathery, and sometimes positioned somewhat opposite of one an- other. When visible, the leaf veins are parallel and run the length of the leaf.
These plants can be part of a healthy ecosystem. For example, they can be consumed by animals such as ducks and beavers and provide a habitat for fish. Under most conditions they do not cause problems, but some species can be problematic (e.g., curly-leaf pondweed; P. crispus). When control is necessary, there are several options for eliminating pondweeds. One option is to stock 5 to 10 triploid grass carp per acre for moderate infestations and 15 or more for severe infestations. Do keep in mind that abundant grass carp can impact other fish and live up to 20 years. One chemical option is to apply Endothall (4.23-pound formulation). Endothall (1.92 gallons per acre-foot of water) should be applied as a submersed injection (application using a wand or hose).
Make sure to determine pond volume prior to application. Read and follow all chemical label instructions, especially the section on the use of personal protection equipment. Treat ponds when the plants are actively growing and the water temperature is at least 60˚F. For larger bodies of water, it is best to treat one-third of the pond at a time. Wait 2 weeks or more between applications.
A repeat whole-pond application may be necessary after the entire pond has been treated to eliminate remaining weeds.
For further information on pondweed control, see Extension Publication P3735-10, Pondweeds.
