MOUNT VERNON, Ohio – Favorable climatic conditions this spring have put pond weed growth several weeks ahead of normal years.
If you’re going to battle those weeds, do it now. According to Troy Cooper, Knox County ag extension agent, late May and early June are the best times to take preventative action against weeds. The best time to apply aquatic herbicides is when the target plants are actively growing and before they flower and produce seed.
Undesirable vegetation in a pond can be controlled mechanically, biologically, or chemically. All three methods should be considered before making a decision to proceed.
Hard work pays off.
Vegetation around the pond edge can be controlled by hand pulling, cutting, or mowing. This can be effective against emergent weeds such as cattails and some submerged weeds and should start in spring when leaves first begin to appear.
By repeatedly removing the leaves on these plants, the energy reserves in the root system become depleted and the plant eventually die, Cooper said, adding that this method requires dedication and persistence throughout the growing season, but can have noticeable results in one growing season.
Biological control involves disrupting plant growth by modifying the aquatic environment through natural manipulation, or it can mean the introduction of a living organism capable of controlling weeds.
Biological control includes the maintenance of a level of fertility high enough to foster a good microscopic plant and animal population in the water. This plankton population will making the water cloudy and prevent the light penetration necessary for weeds to become established.
Cooper warns this form of control requires intensive management and more time than the average pond owner normally devotes to the pond.
The use of the triploid white amur is another form of biological control. The white amur is a sterile, vegetation eating fish also known as a “grass carp.” They can live up to 15 years and weigh 60 pounds or more.
The stocking depends on the percent of pond covered by plants and the types of weeds in the pond.
“White amur tastes are similar to humans. Most of us prefer the ‘dessert’ type foods over the ‘brussels sprout/broccoli’ type foods,” Cooper said. “The same is true with the white amur, they will selectively eat the tasty weeds first and eat the ‘bad tasting’ foods only when there is nothing else to choose from.”
This herbivorous fish should be considered as another tool for aquatic weed control and not as the ultimate solution. White amur represents a biological control option that may reduce the need to use herbicides. Cooper said this can be especially important for those who use their water for potable or livestock uses as well as for managers of larger private lakes where annual aquatic herbicide treatment costs are prohibitive.
When chemical control is the most desirable and/or feasible method of control there are a few steps that should be followed to maximize effective weed control. Those steps include: proper identification of aquatic plant(s), proper herbicide selection and correct application rate and timing.
When collecting plants for identification, every effort should be made to collect samples of each of the different kinds of plants present. Plant specimens should be placed either in a container with water or covered with wet paper towels and placed in a plastic bag.
Once correctly identified the type of herbicide can be determined. The amount of herbicide to be applied varies with the product used. The application rate on the label is usually described on the basis of area (acres of water surface) or volume (acre-feet of water).
In order to apply the proper amount, these characteristics of the pond or lake must be known. It is extremely important to read and follow the label when applying chemicals to a pond.
Proper timing of herbicide/algaecide applications is extremely important for both effective control and to avoid other potential problems, Cooper said. Timing involves knowing what the water temperature is, waiting until vigorous plant growth is present, but not waiting too late in the summer when large quantities of weeds are present.
The danger of applying when there is heavy weed concentrations is the risk of oxygen depletion in the water. As plant material decomposes, oxygen in the water is consumed. If too much plant material is decomposing oxygen levels may be too low for fish to live and a fish kill results.
Early treatment of the water or applying herbicide/algaecide in to sections of the pond are methods to reduce the risk of a fish kill.