Duckweed Control – 7 Ways To Get Rid of Duckweed In Pond

Duckweed is one of the most common pondweed problems. They grow quickly and takes a little time to cover up the whole pond.

Although, duckweed is a portion of good natural food for some fish species, if present in excessive amounts, it can hurt the pond environment and its habitats. In some cases like duckweed in koi pond can have a bad impact on the beauty of the pond. Therefore, controlling their population is a must.

There are several methods of controlling and removing duckweed in a pond or lake. In this article, I will talk about some of the easiest and effective methods that you can apply to kill and get rid of duckweed in a pond.

Use Aquatic Herbicides That Are Safe for Fish

Many aquatic herbicides are available that works effectively on duckweeds. I recommend the following herbicides that are tested by the MDC. These aquatic herbicides will kill duckweed without killing fish if used in a proper dose. You can get a pdf copy of their duckweed and watermeal control guide here.

Sonar AS

Sonar AS is a trading name. The chemical name is Fluridone. It is the safest aquatic herbicide that you can use to kill the duckweed in your pond. Sonar AS doesn’t bring any harm to the pond environment.

The application rate of Sonar As is .25 to .5 Gal per surface acre or as per the manufacturer’s recommendations. There is no restriction on fish consumption and water use of livestock and swimming.

Recommended Product: Sonar RTU Ready-to-Use, 1 Quart

Reward and Weedtrine-D

One of the fastest ways to kill the duckweeds is to use Reward or Weedtrine-D. Reward and Weedtrine-D are the trade name and the chemical name is Diquat. The action is fast as duckweed absorbs it quickly.

The rate of application is 1 to 2 gallons per surface acre of 2L or as per manufacturer recommendation. There is no restriction on fish consumption. But you have to wait at least 5 days to use the water for irrigation, domestic and cattle use.

Recommended Product: Weedtrine D Aquatic Herbicide, 1 gal

Cutrine Plus

Cutrine Plus is Copper Ethanolamine Complex. It is widely used in fish ponds and hatcheries for controlling algae and duckweed. It kills duckweed by breaking the cellular structure.

If you have trout in your lake or pond, then you have to be cautious while using it. Because the carbon hardness of water is less than 50 ppm, it can be toxic to trouts.

Before you use any aquatic herbicide in your pond or lake, make sure it is safe and don’t use overdoes.

These chemicals will surely kill any duckweed they come into contact with. However, killing duckweed in the pond may cause a lack of oxygen in your pond due to the decomposing of the dead duckweed. Therefore you should keep the pond in continuous aeration when the duckweed fully decomposes.

Recommended Product: APPLIED BIOCHEMISTS Cutrine-Plus Algaecide, 1 gal

Use a Pond Net to Collect Duckweed For Your Garden Pond

If you are a small pond owner, you can adopt this method. Use a pond net or pool leaf collecting net for collecting the pondweeds.

Here the wind can help you. When the wind blows, the duckweeds are gathered in one place. From there you can collect them.

When you select a pond net, go for the large one. It will make the job easier.

Use a Parachute Skimmer for Collecting Duckweed

Parachute skimmers are newly introduced and an easy-to-use tool for duckweed removal. It has mainly three parts. The mesh screen retains the duckweeds. A floating device keeps it above the water. And the rope is used to drag it to the shoreline.

This tool is very easy to use. All you have to do is to throw it to the water with pondweed and drag it to the shore by rope. Then you have to collect the duckweeds from the mesh.

Parachute skimmers can be 3 meters wide. You can use this for the effective removal of duckweed in small and medium ponds.

Use Floating Drag Rope or Net to Collect and Remove Duckweed

If you want to remove duckweed from a large pond or lake, you can use a floating drag rope or net. It is an effective and efficient method. This is also very cost-effective and you can make the rope at home.

First, place the rope near the shoreline and close the loop. Then slowly decrease the area and the duckweeds will be dense in that small area.

After that, you can remove them by hand or pond net. Make sure you put the duckweeds far from the pond so that they don’t come back to your pond again.

Use a Mechanical Duckweed Skimmer for Skimming Out Duckweed

A mechanical pondweed skimmer is a motor-driven pond skimming system. It is efficient and eco-friendly.

The working mechanism of a surface skimming system is straightforward. It pumps out the surface water from the pond along with the duckweeds. Then the water goes through a strainer. The strainer separates the water from the duckweeds or any other solids. Then the clean water again goes back to the pond.
You can use a surface skimmer if you have a large pond and budget.

Again for small to medium ponds, low-cost pond skimmers are also available. They are available in two models, regular pond skimmer and floating pond skimmer.

The regular pond skimmer is installed outside of the water. Water is pumped out of the pond and sent to the skimmer. The strainer or mesh separates the duckweeds from the water.

The floating skimmer is placed at the pond. When it runs it pusses the surface water through it and the floating duckweeds are strained in it.

Stock Duckweed Eating Fish

There are many species of fish that feed on aquatic vegetation. But not all of them are effective for duckweed control. This is because most of them will not eat duckweed if they got enough supply of other normal food. The following fish species will eat duckweed in pond.

Grass Carp

Grass carp is the most popular species of fish for aquatic weed control. They primarily feed on aquatic plants. Grass carp can eat up to three times their body weight per day.

If you found that less than 50% of your pond is covered with duckweed, then stock 10 grass carp of 8-12 inches per acre. For coverage of more than 50%, the number will be 15-20.

Tilapia

Tilapia is also a good fish to stock in your pond or lake to control the duckweed. Note that, there are two verities of tilapias, the blue one and the red belly one. You should stock the red belly tilapias because the blue one doesn’t eat duckweed.

Stock up to 30 pounds of small tilapias in one acre. You might also need permission from the eligible authority for stoking tilapias.

Goldfish

If you have a small garden pond then you can have some goldfish in it to control the duckweeds. Duckweed is a favorite food of goldfish. Once you stock some of them in your garden pond, they will finish any duckweed or watermeal.

Koi Fish

Most of the garden pond owners stock koi fish for their beauty. But koi is also good for controlling duckweed in a pond.

You may also find that your koi don’t eat duckweed at all. The reason is simple – they aren’t hungry enough to eat duckweed. What you can do as a solution is to cut their regular food supply to some extent. They will surely eat up the duckweeds.

Have Some Domesticated Duck For Eating Duckweed

Do you know why we call it duckweed?

Because duckweed is the favorite food of duck. Also, wild duck is the source of duckweed in your pond as I have told you earlier.

If you have no problem with keeping ducks, then you can have some domesticated ducks in your pond. The ducks will keep the population of the duckweed at a tolerable limit and you will also get some eggs for free. But don’t forget to feed your duck some extra food twice a day. Also if you have small fish in your pond, you have to think twice before you release the ducks. Ducks can eat them up also.

Things to Do with the Excess Duckweed Removed from the Pond

Although duckweed can be the worst nightmare for any pond owner, it is not totally useless. Duckweed can be used for a lot of things and it seems to work fine because they are enriched with nutrients. You can –

• Compost it into fertilizer for other plants.
• Feed it to animals that can digest plants, such as hens, ducks, and goats.
• Put duckweed under trees and around shrubs for an organic, free mulch.
• Use the leaves as compost in greenhouses. It converts into nitrogen compounds which provide plant food.

Best Way to Get Rid of Duckweed Naturally

The natural duckweed control method works best when the population of duckweed isn’t very high in the pond. You can follow the following preventive measure to get rid of duckweed naturally.

• Give your fish the exact amount of food that can eat. Excess food increases the amount of nutrition in water which triggers the growth of duckweed.
• Stock duckweed eating fish and domesticated duck in your pond or lake.
• Don’t let leaves fall in the pond and collect the falling leaves. They increase nutrition in water which helps duckweed grow.
• Use barley straw. It is a good method of controlling it.

Causes of Duckweed in a Pond

Duckweed, a type of aquatic plant, will not only thrive in an unmanaged pond or lake but can also spread quickly because it has no roots and reproduces by fragmentation.

There are many causes for duckweed to form; however, the most important contributor is nutrients from fertilizers, septic tanks, storm runoff as well as animal waste from gardens or pastures upstream of the pond.

Organic wastes include nitrogen (N) and phosphorous (P) compounds that stay in the soil, preventing them from entering into the water. When these fertilizers enter a waterway, they create more fertile ground for duckweed growth.

Frequently Asked Question (FAQ)

Should I remove duckweed?

It depends on the population of duckweed in your pond. If the population of duckweed is very high, say more than 1/4th of your pond is covered with duckweed then you should definitely remove them. Duckweeds are beneficial for your pond when they are present in a small number.

Is duckweed good for a pond?

Duckweed is good for a pond for many reasons when they are present in a moderate number in your pond. Some of the benefits of duckweed are –

• They are good natural food for some of the fish like Koi, Goldfish, and Grass Carp.
• Duckweed is a good natural filter for a pond as it can absorb bad materials out of water.
• It gives shade to the pond.
• Working as a cover, it can save the fish from predators.

What animals eat duckweed?

Duckweed is eaten by ducks, muskrats, mink, carp, goldfish, frogs, and turtles. That being said these only count as eating animals in the wild who are not fed duckweed.

There are bugs that eat duckweed such as dragonfly larvae or moth larva but those don’t count because they grow out of the nutrient-rich water where duckweed grows.

Will vinegar kill duckweed?

Vinegar can kill some types of pondweeds and algae. However, it is not very effective for duckweed. Although vinegar is safe for fish and other pond habitats, you shouldn’t use a large amount of it at a time in the pond. That can be harmful to the fish. So it is not a good way to control duckweed with vinegar.

Will salt kill duckweed?

A tablespoon of salt mixed with a gallon of water will kill most of the duckweed. Salt contains sodium, which can quickly balance the acidic levels in the duackweed’s fluids which cause cellular damage and eventual death.

Always be sure to mix a lot of salt into a small amount of water before boiling, because it doesn’t work very well when just sprinkled on top of the duckweed.

Does copper sulfate kill duckweed?

No, Copper Sulphate alone can’t kill duckweed. But you can use Copper Sulphate along with Diquat. This gives the best result when you want to use a chemical herbicide to control duckweed.

Does duckweed die off in winter?

In areas where winters are mild, duckweed will stay alive; in cold regions (US Zone 3), duckweed may die for periods of time. Coldwater inhibits the plants’ growth and metabolism.

They’ll come back when water temperatures rise above 40F/4C and there’s plenty of sunlight. They may not return to their pre-winter peak population density with the same vigor they had before winter set in, but they’ll eventually bounce back to a workable level again after sufficient rest and recovery time.

Does barley straw get rid of duckweed?

Barley straw doesn’t directly kill duckweed. But it works to some extent to keep their population in control. Therefore, it can be a good way to control duckweed in a pond.

How do I get rid of duckweed in a large pond?

Treating duckweed in a large pond can be tricky. You can adopt the following control and removal method for getting rid of duckweed in a large pond.

• Stock duckweed eating fish.
• Collect and remove them with an effective collection system like a large net or skimmer.
• Kill them using a duckweed killer.
• Keep the amount of nutrition in your pond low so they don’t grow quickly.

Why is duckweed bad?

Excessive duckweed in ponds and lakes is bad for a number of reasons. They create the following problem –

• It blocks the sunlight from reaching the pond water.
• It houses bad insects and disease-creating organisms.
• Dead duckweed creates a lot of debris in the pond that finally results in an algae bloom.
• It boosts the growth of anaerobic bacteria that are harmful to the pond.
• Prevents the growth of good algae and submerged pondweed that oxygenate the pond water.

How fast does duckweed multiply?

Duckweed grows really quick. If enough nutrition is available in water it can divide once a day. A couple of duckweeds can cover the whole pond within one and a half months.

Will duckweed kill fish?

Although duckweed will not directly kill fish, its long-term effect can result in fish death. It can heavily contaminate the pond water and create a lack of oxygen in the pond water. This can lead to fish death. Also, this facilitates the housing and growth of disease-creating organisms that can cause fish death.

Does duckweed oxygenate water?

Duckweeds aren’t any good for oxygenating water. As duckweed are floating pond plants, the oxygen they deliver goes directly to the air, not in the water because photosynthesis occurs in the upper layer. For oxygenating pond water, submerged pond plants help the best.

Where does duckweed come from?

Many pond owners wonder, where did they end up getting so much duckweed in their pond when they haven’t released any duckweed themselves. But duckweed can migrate to your pond in many ways that you might not think of. Like –

• Most of the time duckweed is carried by the wild waterfowl. While roaming in the source, duckweed is attached to their body. Again when they come to your pond, they leave duckweed in your pond from where it grows and finally covers up your pond.
• Another source of duckweed is the pond plants collected from sources where duckweed is present.
• If you take any pond maintenance service, their instrument can be a carrier of duckweed.

It is better you prevent duckweed from entering your pond rather than controlling and removing duckweed when they have covered up your pond. So, take the necessary measures so that you don’t face this problem in the future.

I hope these methods will be helpful for you with duckweed control.