Nevada County Picayune and Gurdon Times Newspaper Archive

Farm and Home News

Weeds can be a real problem for farm pond owners. Excessive growth of weeds can interfere with watering cattle and fishing. Floating weeds, such as duckweed, can become so abundant that the pond surface becomes covered, cutting off light and oxygen to the fish below.

Some growth of aquatic plants is very beneficial for wildlife, and these plants form part of a healthy pond. However, on occasion weeds can literally take over a pond and cause serious problems for the farm pond owner.

The best way to avoid weed problems is prevention. When constructing a pond avoid leaving shallow areas with water depths of less than 2= to 3 feet. These areas are ideal for the growth of rooted aquatic weeds. Excess nutrients from livestock or other sources that run off into a pond can also lead to weed problems, especially the growth of filamentous algae.

The first step in weed control is to properly identify the problem weed. The most effective control method varies with the kind of plant, so be sure to determine just which weed is causing problems.

Control measures for weeds may be physical, biological, chemical or a combination of these techniques. For small patches of weeds pulling out plants by hand or with a rake can be effective. Usually this has to be repeated a number of times, because the weeds will keep coming back. Winter drawdown, where the level of water in a pond is lowered in the fall, can reduce certain weed problems by exposing aquatic plants to freezing temperatures.

The grass carp, or white Amur, is a fish that eats a variety of aquatic weeds, and is a valuable biological control method. Grass carp can provide long term cost-effective control of certain weeds. Ponds with an existing weed problem should be stocked with grass carp to help control the weeds. However, it may take a year or so to see the results. Stocking rates for grass carp vary from 5 to 20 or more per acre, depending on the extent of the weed problem.

Chemical control of weeds using herbicides may be necessary as a last resort, and many times repeated treatments are required. It is particularly important to properly identify the problem weed for chemical control to be effective. Be sure to follow label instructions and note that use of a chemical may restrict other uses of the pond, such as irrigation or watering cattle, for certain periods. Chemical treatment may be used in combination with grass carp, where a herbicide is used to reduce the amount of weeds, followed by the stocking of grass carp to reduce re-growth of the weeds.

Some weed problems are seasonal. A typical problem in late winter and early spring is the growth of filamentous algae, commonly called pond moss. Bunches of green, thread-like strands of algae can cover the pond bottom and float up to the surface in the form of unsightly mats or clumps.

Spring is generally the best time to chemically control weeds. Plants are growing rapidly and water temperatures are cooler.

Decomposition of weeds that are killed by herbicides removes oxygen from the water and can even result in fish kills, especially in the summer months. Treating only a portion of a pond at one time will minimize oxygen problems.

For assistance in controlling farm pond weeds contact your local Extension office.