How do I control milfoil in one acre pond? Would a combination of blue dye...

Asked March 12, 2013, 9:09 AM EDT

How do I control milfoil in one acre pond? Would a combination of blue dye and 10 Amur work?

Ottawa County Ohio

1 Response

Milfoil can be an aggressive plant and needs to be controlled early in the growing season. Eurasian watermilfoil is a perennial plant native to Europe, Asia, and Africa and was probably brought to the U.S. as an aquarium plant. It is considered one of the most aggressive and problematic plants in the U.S. because of the dense colonies which it forms. The stems are multi-branched, somewhat reddish in color, with gray-greenish feather-like leaves. The leaves are in whorls of 3 to 5 around the stem with each leaf divided into 12 or more pairs of thin thread-like leaflets. Reddish flowers are borne on leafless spikes that rise above the surface a few inches. Eurasian watermilfoil is a very aggressive, non-native weed, but other milfoil species are beneficial natives. Eurasian watermilfoil can spread from seeds or by fragmentation. Submersed plants can be controlled with a variety of methods, including the grass carp, mechanical harvesting, dyes and aquatic herbicides. However, the grass carp is not very effective in controlling Eurasian watermilfoil. Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Dye concentration must be maintained throughout the growing season, so its use is limited to ponds with no outflow. Also, it must be applied before weeds emerge in the spring; once weeds reach the water surface, the dye has little effect. In Ohio a second application may be required during the summer. Aquatic herbicides can be used to control watermilfoil. When using any herbicide, please read the product label for possible restrictions and personal safety. These water restrictions can vary from no restrictions to several days or weeks depending on product being applied and on how the pond is being used. Treatment of aquatic weeds should take place in the spring as the weeds begin active growth. It is important to adhere to this application suggestion, even if an infestation is small. Later in the season, weed density and maturity make conĀ­trol more difficult. Sampling the bottom in the late spring or early summer in areas heavily infested the year before should show when the growth begins. The treatment of dense weed growth can result in oxygen depletion during the decomposition of the dead plants. Severe oxygen depletion can cause a fish kill. It may be necessary to treat only 1/3 to 1/2 of the impoundment at a time. As for chemical treatment, Aquathol and Reward are the most commonly used chemicals for submersed plant control. They can be tank mixed with copper products to control both algae and submersed plants. They act quickly, and burn-down should be visible within a week of treatment. Although these herbicides are extremely short-lived in water, be aware of restrictions based on pond use. Although burn-down of Eurasian watermilfoil can be achieved with Aquathol and Reward, this invasive species is more effectively controlled with 2,4-D (Navigate or Aquakleen), triclopyr (Renovate 3) or fluridone (Sonar or Avast!). Although the fluridone products are quite expensive, they can be used at extremely low dosages to remove Eurasian watermilfoil from native plant stands. In summary, when choosing an aquatic weed control program, identify the weed problem and consider the use of the site before choosing a control method. If herbicides are chosen, use them at the recommended rates, apply them properly, and be sure to follow all use restrictions. Improper application rates, incorrect formulations, or faulty application may cause a fish kill or seriously alter the food chain, slowing the growth rate of fish. If you have any additional questions, please let us know. Thank you.