Getting Rid of Nuisance Plants in Missouri Ponds and Lakes

By University of Mo. Extension

First posted on 05-23-2014

Unwanted aquatic plants are the number-one pond maintenance problem in Missouri.

These unwanted plants make their appearance every year with the arrival of warmer temperatures, and continue to annoy pond owners throughout the summer and fall.

“A number of water plants are good for a pond or lake. But, when they are growing rampantly they should be controlled,” said Patrick Byers, horticulture specialist, University of Missouri Extension.

Water plants have some very good attributes. Water plants put dissolved oxygen into the water. They provide food for fish or other wildlife. They also provide nesting and breeding habitat for fish and other animals, and they help with erosion control by minimizing wave damage to shorelines.

“Water plants also have a downside. Excessive growth of aquatic weeds can interfere with recreational activities, create health hazards, destroy wildlife habitat, cause undesirable odors and kill fish,” said Byers.

The first step to good weed control in a lake or pond is first determining whether you have a problem that needs attention. Second, it is important to identify the problem weed.

“The last step is controlling water plants by the careful use of herbicides or various non-chemical methods,” said Byers.

Before choosing an herbicide, Byers recommends carefully reading the label to learn which plants can be controlled, and when to apply. Also check for the safety of humans, livestock and fish. The label is the final authority

“Chemical control is not permanent; re-treatment may be necessary, and it can become quite expensive. That is why non-chemical methods are also important to consider,” said Byers.

Possible non-chemical methods for water plant control include stocking the pond with grass carp, deepening the pond’s edges, weeding and removing new growth by hand or shading the pond with black plastic to prevent sunlight from reaching the plants.

“Another key step is the elimination of nutrient sources. Runoff from animal manure, septic tank fields and fertilizer encourages weed growth. Keep these nutrient sources away from ponds or divert the runoff and the plant growth should slow down,” said Byers.

For more help with weed control in lakes and ponds contact your local University of Missouri Extension Center to request guide sheet 4856, “Aquatic Weed Control in Missouri,” or contact the Missouri Department of Conservation, Fisheries Management Division.

For additional gardening and horticultural advice, contact the Greene County Master Gardener Hotline, (417) 881-8909.