How to Get Rid of Duckweed

What Is Duckweed Exactly?

Duckweed is a bright green, free-floating plant that is visible on the surface of a pond, lake, or slough. It is recognizable by its flat clover shape with two to five very small fronds (clover leaves), and one root that hangs beneath the surface. Duckweed is one of the smallest flowering plants known to exist; a single duckweed plant is only approximately 1/16 to 1/8 inch long. Although an individual plant is so small, duckweed floats in large colonies that can become quite noticeable. Duckweed reproduces very quickly in favorable conditions; in fertile water, it can double in just three to five days. While duckweed can offer some benefits to your waterbody, it often becomes a nuisance to pond owners. The following will discuss duckweed in more detail and go over some issues it can present to a pond owner, and steps you can take to combat it.

Where Does Duckweed Come From?

Duckweed is most often introduced to ponds by waterfowl and other animals. Once in a pond, duckweed reproduces by pollination via flies, mites, small spiders, and even bees. More often, duckweed propagates asexually by creating chains of stems from vegetative buds. Some species of duckweed can also produce buds called turions, which are vegetative buds that break off from their parental stems and sink to the bottom of a lake or pond in the winter, where they lay dormant until the spring. In spring, the turions rapidly begin to metabolize, which causes them to float back to the surface of the water where they develop into a mature duckweed stem.

Do I Need to Remove Duckweed From My Pond?

As mentioned earlier, duckweed is not all bad. In the right amounts, it can be beneficial to a pond’s ecosystem. Duckweed provides a valuable food source for birds and other animals and can act as a useful habitat for micro/macro invertebrates and other aquatic wildlife. However, if duckweed reproduces to the point that it covers a significant portion of your pond, it can be very disruptive. Like all plants, duckweed produces oxygen when sunlight is available and consumes oxygen when sunlight is not available. In certain cases – like in the summer, when water is warmer, or on cloudy days – duckweed may consume more oxygen than it produces, which can decrease oxygen in the water to dangerous levels for fish. Additionally, the shade created by large amounts of duckweed on the water’s surface can lead to stratification (water separating into warmer and colder levels), especially in deeper ponds. The colder water can accumulate toxic compounds and when heavy rain or wind occurs, these colder layers mix with the rest of the water, leading to fish kills or reduced fish growth. The reduced sunlight penetration caused by excessive duckweed growth can also unbalance the pond’s ecosystem by eliminating other aquatic vegetation.

It is therefore important to monitor the amount of duckweed growing in the pond. If the growth becomes uncontrolled and a significant portion of the pond’s surface is covered with duckweed, steps should be taken to resolve the problem quickly. Luckily, you have options at your disposal. The next section will go over some of these options to help you figure out how to best deal with duckweed.

Should I Use Herbicides (Chemicals) to Remove Duckweed?

There are a number of EPA-approved herbicides available to you to manage duckweed growth in a way that is safe for the fish and wildlife in the pond as well as the people that use the pond. Herbicides are the option most likely to enable you to completely eliminate a serious duckweed problem. Lake Restoration’s best-selling herbicides for duckweed management are Dibrox® and Spritflo®. Using herbicides will still require you to continuously manage your pond to keep duckweed under control in summer months, and it may take years of successful treatment to eliminate or remove duckweed completely from the pond, as you will have to deplete all stores of buds in the sediment. To speed up this process, consider using Lake Restoration’s SparKlear®, which can help dissolve the muck at the bottom of your pond that is holding these buds.

Other methods you can use to deal with duckweed involve manual or biological controls. You can manually remove duckweed by simply raking or skimming the duckweed off the pond’s surface. You can also turn to biological controls, like introducing grass carp into your pond as they eat duckweed. However, the fish might eat other vegetation in your pond in addition to or instead of duckweed. If the pond is highly eutrophic (nutrient-rich), duckweed re-growth can outpace the carp. Additionally, to introduce grass carp into your pond, you must obtain a state permit and purchase the carp from an approved hatchery.

You can also take steps to slow or deter the growth of duckweed rather than remove it. Duckweed tends to prefer slow-moving or stagnant water, so installing a pond aerator will curb duckweed growth by keeping the water in constant motion. Removing excess nutrients in the water can also help limit the extent to which duckweed can thrive in your pond. Again, SparKlear® can dissolve the muck and organic nutrients at the bottom of your pond that feed duckweed growth. Additionally, phosphorus is a major nutrient for duckweed growth. PhosControl® can be applied to eliminate free-phosphorus from the water. While these are useful steps, these indirect methods will never completely eliminate the problem.

Can I keep Duckweed out of my pond?

The best case scenario for you and your pond is to avoid a duckweed problem altogether. One of the best ways to do this is to prevent waterfowl access to your waterbody. Waterfowl are the number one source of duckweed introduction into ponds. In addition to waterfowl, land mammals and other animals can also carry duckweed from surrounding bodies of water into your pond. One option to check out is Lake Restoration’s Goose D-Fence®, which is a specially engineered, retractable fence for goose control. It will keep waterfowl out of your pond, can be installed or removed in less than 10 minutes, and practically goes unnoticed.

Conclusion

As a pond owner it is vital that you come up with a duckweed control management plan. Using some combination of the tips above should allow you to come up with a strategy that can effectively combat duckweed overgrowth and prevent the buildup of duckweed and dormant buds in your pond. It is important that you are proactive with your plan, so as soon as you become aware of duckweed in your pond, use your chosen management strategy early and often so that controlling duckweed is as quick and easy as possible.