Pond Weed Control And Treatments

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Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

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There are many things that can grow in a large pond or lake. Algae is one of the more common things you’ll find but along with that, or in place of it, a pond weed will take root and sometimes take over a pond or water way.  Some of these aquatic weeds can be very invasive and the more well established they become the harder they can be to control.  In this article we’ll talk about some of the more common pond weeds one might find across North America and we’ll provide some tips on the best ways to control them.

Cattails And Emergent Plants

By definition, emergent plants grow mostly around a pond, in shallow waters or along the shoreline. For most of us around the U.S. the most common of these would be cattails, reeds, Pennywort, or Bulrush. Because they are usually within easy reach, many people try to remove these manually by using a pond weed rake, or with some heavy equipment and often enough this can help keep them in check for a time.

If a pond owner is unable to physically remove the plants then an aquatic herbicide is likely the best option, and this generally goes for any type of aquatic weed as well. Remove them if you can, treatment if you must. A product called Shore Klear, combined with an activator such as Cide Kick is usually recommended to treat emergent plants. Shore Klear is sprayed directly on the plant and is only good for those that extend above the water’s surface. It doesn’t work well with submerged growth, however it is highly targetable and works well on many emergent pond weeds.

The Pondweed Familly

The term “pondweed” actually represents a species of plants that has over a dozen varieties of pond weeds that can be found in large ponds. A few of the more common plants include Curly Leaf, Large Leaf, Clasping Leaf, and Sago. It’s not as critical to determine the variety since treatments are consistent within the entire family. You’ll know you have a pondweed species when you see fairly long, vine like stems, with leaves branching off of them at different spots. Most leaves are long and slender however this can vary a bit. Sago as an example doesn’t have leaves to speak of, and you may only see very small vine extensions coming off the main stem. This type of plant can sometimes grow in water as deep as ten feet if it is pretty clear and you’ll often see it extending to the surface where it will spread out.

Several broad spectrum aquatic herbicides will work well on pondweeds. Aquathol Super K and Hydrothol are both granular products that can be broadcast over the plant growth and will usually work well to control growth.

Duckweed And Watermeal

Duckweed is one of the more obvious pond weeds since it only floats on the surface of a pond. It’s fast growing and can overtake a large body of water pretty quickly. Free-floating blooms of it will be blown by the wind and may move around the surface of the pond. If you look at duckweed closely you’ll see a somewhat flat, pod-like pellet that has several hair like roots coming off of it. In great numbers they may appear to be a solid mass on the water but they are in fact, individual plants that are pulling their nutrient support directly from the water.

A pond may go without having any issues with duckweed for many years, however the plant can come in, while attached to waterfowl and when conditions are right it will bloom, seemingly out of nowhere.

Watermeal is similar to duckweed however in appearance it’s much smaller in size with what appears to be very fine green grains however once again, when these are dense enough they will cover the surface of a pond.

Physical removal of duckweed is sometimes possible but usually the best course to take is to use some type of herbicide to control the plant. These should ideally be applied early on in the growth, before it becomes widespread on a pond. A product called Sonar, which contains a chemical called fluridone is usually suggested for duckweed control. White Cap is another brand. For a more eco-friendly option a new product on the market called Elemna8 may provide desirable results as well.

Waterlilies Are Good But…

Waterlilies add beauty to any pond that they grow in. No question about that. They also can help provide shade and protection for fish, and work to outcompete unwanted plants like algae. However waterlilies are also really good at growing and they can overtake a pond if they are not managed somewhat.

If you find that waterlilies are getting the upper hand there are several things you can do. Manual removal is an option if they’re not too heavy. Apart from that a product called Navigate can be applied to control them. After blossoms have appeared Shore Klear can be used to good effect.

Invasive Plants Include Hydrilla And Water Hyacinth

Of all the pond weeds that may cause problems for larger ponds, there are several that are so invasive, fast growing, and prolific, that they are now creating a number of issues in various states around the country. Water Hyacinth (Eichornia crasipes) for example is a plant that’s actually native to South America. It’s actually a popular plant to add to small ponds and water gardens, however it infested freshwater areas from the east cost to the west coast and is very troublesome in the southeast U.S. in particular. In many cases a non-native species can harm desirable local species as it chokes them out over time.

Other waters which may be used for irrigation or cooling can become infested and clog up systems or in the case of Hydrilla in Texas, some lakes there have become so heavily burdened that recreation and navigation are being restricted.

It doesn’t take much of the plant to get a foothold and since conditions are often ideal in the southern United States, the plants can grow and spread very quickly. Some control measures include various herbicides but there are also trials underway using biocontrols. M. scutellaris is a small bug native to South American that feeds very specifically on water hyacinth and they may provide a non-chemical way to keep the plants in check.

Where invasive plants are concerned, the best option is to limit their spread by simply not introducing them into the area’s water ecosystem. Small pond and aquarium owners who may benefit from the plant need to make sure they are disposed of properly. If they are removed from the pond or tank, be sure they are dead for about two days before disposing or insure that they come nowhere near a water source of any kind. It has shown the ability to survive in water in trash cans or buckets. They should never be dumped live into a a nearby lake or stream as they wil likely infect the water in short order.

Pond Weed Control Tips

Along with the recommendations that we’ve included for various plants, as a general rule it’s best to attempt the treatment of many pond weeds as early as possible in the growing season. Most species don’t grow well in cold or cooler weather and in many parts of the country that may freeze in the winter, the plants will go away entirely only to return again in the spring. Treating as the plant is just emerging will often allow less use of any chemicals simply because the plant may be more isolated, and they tend to be weaker at that time as well. This also tends to be much safer for fish populations because during any treatment where a rapid die off of plants occur there is the chance of oxygen depletion in the water.

It’s also important to clearly identify what the plant is that you have growing in your pond. Ideally you don’t want to guess and just simply start trying to treat it. Many species require specific types of products for the best control. The University of Florida offers a helpful website for aquatic plant identification as does Texas A & M University. Use these resources if you’re not absolutely sure of what you have growing in your pond or lake.

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