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Aquatic Weed Control for Lakes and Ponds

By Pond King

All fish need cover at some point in their lives, so some aquatic vegetation is good. However, if left unchecked, aquatic vegetation can become a real threat to the health of your fishery.

Some Aquatic Vegetation is a Good Thing

We talk about it all the time - all fish need cover at some point in their lives. So, some aquatic vegetation is a good thing. However, if left unchecked, aquatic vegetation can become a nuisance at best and, in some cases, a real threat to the health of your fishery. So, if you have a lake or a pond on your property, at some point in time, you're probably going to have an issue with aquatic weeds.

Prevention vs. Treatment of Aquatic Vegetation

Aquatic vegetation growth rates typically kick into high gear when water temperatures are consistently above 60 degrees. As the old saying goes, an ounce of prevention is worth a pound of cure. We have several blog posts about pond management options for aquatic weed control where you can read more about prevention, and one of the most effective ways to prevent aquatic vegetation from getting out of hand is by limiting the amount of sunlight reaching the bottom of your pond. You can do this by either dying or fertilizing your pond or lake - and which technique you choose will be dependent on the size of your fishery. Unfortunately, even with constant vigilance, weeds usually find a way to proliferate. When that happens, knowing how to control the weeds without harming your fishery is paramount. 

Important Notes about Treating Aquatic Vegetation

Not all vegetation is bad. In fact, fish do better when there is some vegetation in your fishery. To learn about the different types of aquatic vegetation and their respective pros and cons, check out our blog "Types of Aquatic Vegetation." But if it gets out of hand, here are several important notes to keep in mind when treating aquatic vegetation.
  1. If you decide to use a chemical treatment, it is imperative that you purchase products rated for aquatic use.
  2. Follow the instructions on the label, for application rate, targeted species, and protective equipment. For more information about application rates, please contact us directly at askapro@pondking.com.
  3. Only treat a small portion (20%-25%) of the total pond surface area at a time. This will prevent depletion in dissolved oxygen concentration as the plant biomass decomposes. Additionally, we recommend waiting 2-3 weeks between treatments. And, if there are multiple species present that require different chemicals, focus on the most prevalent first and work one species at a time.
  4. When using chemical treatments in elevated water temperatures during the summer, treat a smaller portion than normal. Dissolved oxygen concentrations decrease as water temperatures increase, also increasing the risk of oxygen depletion, so you need to exercise additional caution in this scenario. 

You can read more about these cautionary warnings in our blog: "Will Controlling Aquatic Vegetation with Herbicides Kill My Fish." 

Identifying, Treating, and Preventing Aquatic Vegetation

Here is a list of the aquatic plants which are most likely to be troubling you and our respective treatment recommendations. If you don't see your particular problem plant here, that doesn't mean we can't help you get it under control; it just means it isn't something we see a lot here in North Central Texas. 

American pondweed: 

American-pondweedWe have some customers who add American pondweed to their pond because it helps attract waterfowl. It typically roots in shallow water and is characterized by blade-shaped floating leaves. A small seed head will protrude above the water's surface on a small stalk during the summer. Unfortunately, while it may help attract ducks to your pond, this native plant can quickly get out of control.

Chemical treatment for American pondweed: We recommend a product called Aquathol K, a dipotassium salt of endothall as a contact herbicide. Aquathol K should be treated at a rate of 1.5 gallons per acre-foot of water (liquid) or 13lbs pounds per acre-foot of water (granular). A systemic herbicide option for treating American Pondweed would be Sonar RTU (liquid), or Sonar One (granular) containing the active ingredient Fluridone. Systemic herbicides act slower than contact herbicides as they must be absorbed by the plants in order to move to a sight of activation.

Pond management techniques for managing American pondweed: Since American pondweed grows from the bottom up, a very effective biological control method is Triploid Grass Carp. Even though these fish are sterile (triploid), they are considered an invasive species, and if you live in Texas, you will need a permit from the Texas Parks and Wildlife Department to stock them. You can apply for that online at tpwd.org.

Bushy pondweed (Southern Naiad): 

Pondweed-1-Bushy-PondweedLike American pondweed, Brushy pondweed is a native plant that roots in the bottom of the pond and grows up to the surface. It has thread-like narrow leaves with microscopic teeth along the edges. The leaves grow opposite each other on slender, sparsely branched stems, and the plant reproduces by seed germination and fragmentation, like Bermuda grass. It prefers water with a high mineral content (hard water) and can be found growing in water ten or more feet deep.

Chemical treatment for Brushy pondweed: While Flurodine is also an option for treating Brushy pondweed, we typically recommend a Diquat such as Reward or an Dipotassium salt of endothall such as Aquathol K or Aquathol Super K Granular instead.

Pond management techniques for managing Brushy pondweed: Grass Carp can be very effective in managing Brushy pondweed. We have had customers ask what to feed their Grass Carp once they have eaten all the weeds, but don't worry. The Grass Carp don't kill the plants, so they continue to provide nutrients to the Carp. But, once your Carp reach full maturity, they won't eat as much, so you may need to restock them. When that happens, you may need to reapply for a new permit.

Cattails: 

cattailsWith their brown cigar-shaped head that stands atop a very long, stout stalk, Cattails are easy to identify. Cattails are perennial plants that can provide quite many benefits to your fishery. They provide hiding places for your juvenile fish, habitat for redwing blackbirds and other species, and are shockingly nutritious for humans. They can help with erosion control and have even been found to filter pollutants. But, the plant emerges from creeping rhizomes which can spread along your shoreline and, if left unchecked, can turn your beautiful pond into a marsh and, eventually, an open field.

Chemical treatment for Cattails: If your Cattails are getting out of control and you aren't quite adventurous enough to harvest them for the dinner table, we recommend using aquatic-rated glyphosate at a mixture of 8oz per gallon of water with the addition of a surfactant. The brand we carry is ShoreKlear-Plus. You'll want to spray the herbicide on the area with Cattails when they are at least 12 inches out of the water. When the Cattails turn brown and wilt, remove them using a rake. If you don't get the entire plant, including the roots, the Cattails will decompose and provide excellent fertilizer for next year's crop, which defeats the point of removing them in the first place. 

Pond management techniques for managing Cattails: If you are adding Cattails to your pond for aesthetics, a great way to control them is to plant them in pots to prevent the rhizomes from spreading. If they do get out of hand, non-chemical methods of control include hand pulling, mowing, and cutting. 

Chara: 

Man-holding-CharaAlso known as Skunkweed or Muskgrass, Chara is a gray-green branched alga often confused with submerged rooted plants. Chara has no flower, does not extend above the water's surface, and usually has a grainy or crunchy texture because of the calcium deposits on its surface. Chara has cylindrical, whorled branches with six to sixteen "branchlets" around each node, and if you break it, you'll notice a musky odor - hence the common name Skunkweed.  

Chemical treatment for Skunkweed: For treating Chara, you can use we recommend either Cutrine Plus (liquid) or Cutrine Plus Granular. We prefer the Granular because waters treated with this product may be used for swimming, fishing, further potable water treatment, livestock watering or irrigating turf, ornamental plants, or crops immediately after treatment. Don't use either in ponds with Koi or hybrid goldfish.

Pond management techniques for managing Skunkweed: Even though Chara is technically algae, if you want to use a biological method of controlling this plan, you should stock Triploid Grass Carp. In Texas, the state will determine the appropriate number of fish for your pond. But, typically, you will want five Carp per acre if the water body has less than 50% plant coverage and 10 per acre if plant coverage is greater than 50%.

Coontail: 

coontailCoontail is a bushy-looking grass with whorls of stiff, forked leaves along densely branched stems, resembling a raccoon's bushy tail - especially when submerged. Despite its appearance of growing from the bottom up, Coontail does not have a root structure to hold it in place, so it can move and amass along the shore. Like so many other weeds, it can provide food and habitat to fish and waterfowl throughout the year. But, it can hinder fishing and contribute to oxygen depletion when it gets out of hand. 

Chemical treatment for Coontail: To chemically control Coontail, we use Reward or AquatholK.

Pond management techniques for managing Coontail:  The biological control for Coontail is Triploid Grass Carp. You will want five Carp per acre if the water body has less than 50% plant coverage and 10 per acre if plant coverage is greater than 50%. If you live in Texas, you need a Texas Parks and Wildlife Department permit to stock this invasive species in your fishery legally.

Creeping Water Primrose: 

creeping-water-primroseThis is a highly invasive species that offers very little benefit to a fishery but can cause many problems. Water Primrose is a perennial plant that grows along the shoreline and can become a breeding ground for mosquitos and degrade the water quality for fish and wildlife. Water Primrose can be identified by its dense, sprawling mat of alternately arranged, slightly hairy, willow-like leaves and bright, yellow flowers, usually with five petals.  

Chemical treatment for Creeping Water Primrose: If you notice any Water Primrose, we recommend you treat it immediately to prevent it from becoming a problem. Because it is such an invasive species, we recommend physically removing the plant and then treating the area of infestation with aquatic glyphosates, like ShoreKlear-Plus. 

Pond management techniques for managing Water Primrose: There is no managing Water Primrose. If you have it, you want to get rid of it. At the time of this post, the only form of suggested biological control is goats because, let's face it, goats will eat almost anything. But, removal and chemical treatments are your best options.

Duckweed:

duck-swimming-in-duckweedA small, green, free-floating plant that is sometimes used to attract waterfowl. Unfortunately, ducks often cannot consume enough of it to keep it under control, and it can quickly get out of hand. In addition, if Duckweed covers the entire surface, it can cause a noticeable reduction of dissolved oxygen content—which can cause fish kills. 

Chemical treatment for Duckweed: Unlike diquat, an herbicide that kills plants on contact, Fluridone is a systemic herbicide that moves slowly into plants to kill them. As a general rule, Fluridone, in the format of Sonar RT, is very effective for the control of Duckweed because it doesn't just destroy the foliage; it kills the roots as well. 

Pond management techniques for managing Duckweed: There are several non-chemical options for preventing and controlling Duckweed: you can stock Mozambique Tilapia, add aeration, or both. Tilapia will help control the Duckweed and any filamentous algae you might have and are also excellent forage for your largemouth bass. Depending on the Duckweed coverage, you'll want to stock 15-30 pounds of Tilapia per acre. Since Duckweed prefers slow-moving, stagnant water, aeration can help discourage growth - and is great insurance against a fish kill caused by oxygen depletion. As you can see, choosing both these options has benefits beyond weed control. If your budget allows, we recommend both for a healthy Bass fishery. 

Filamentous algae: 

filamentous-algeaFilamentous algae is often found attached to other plants, sticks, leaves, rocks, and mud, and resembles mats of wet wool, hair, cotton, or slime. Filamentous algae is typically a greenish color but can become yellowish, grayish, or brownish. Filamentous algae occur naturally in most surface waters, and as it grows, it stretches to the surface and often breaks up, lending new growth to be transported around the pond by wind and wave action.

Chemical treatment for Filamentous algae: Our chemical of choice for treating Filamentous algae is Cutrine, but we chose between liquid or granular based on the amount of growth. So if you have a lot of Filmanetous algae, say 30% coverage or more, we recommend the liquid. But, if you only have moderate amounts of coverage, or less than 30%, then we recommend the granular. In either situation, you only want to treat small areas at a time, especially if the water temperature is over 70 degrees. Otherwise, you could deplete the oxygen levels in your fishery, causing a fish kill. 

Pond management techniques for managing Filamentous algae: Like Duckweed, there are several biological control methods for controlling Filamentous algae: you can stock Mozambique Tilapia, add aeration, or both. Tilapia will consume filamentous algae and are also excellent forage for your largemouth bass. We recommend stocking 10-15 pounds of Tilapia per acre to control Filamentous algae. Adding aeration can help also discourage growth - and is great insurance against a fish kill caused by oxygen depletion. If your budget allows, we recommend both for a healthy Bass fishery. 

Lily Pads: 

Lily-padsLily pads are often added to ponds and lakes to enhance aesthetics and provide cover for your fish, especially in Koi ponds. They are lovely plants with broad, green leaves and white or yellow flowers that bloom throughout the summer. Unfortunately, while they can add charm and beauty to your ponds and lakes, they can easily get out of control, making it difficult to fish and, as with other aquatic vegetation, increase the likelihood of an oxygen depletion event. 

Chemical treatment for Lily Pads: To chemically treat Lily Pads, we recommend a combination of ShoreKlear-Plus, an aquatic-rated glyphosate, combined with a surface-active agent, such as Cygnet Plus. 

Pond management techniques for managing Lily Pads: While nearly all fish species will appreciate the cover Lily Pads provide, no species will contribute to their biological control. The two best options are: 

  1. If you add Lily Pads to your pond, plant them in pots to limit their spread. 
  2. Lily Pads like stagnant water, so surface aerators and fountains can help contain their spread. 
Chemical Pond Weed Control Precautions

Because it is so important, it is worth mentioning again, if you have a problem with an aquatic weed infestation, you must use extreme caution when using a chemical treatment: 

  1. Only use herbicides rated for aquatic use. 
  2. Follow the label.
  3. Only treat small areas of the pond's surface at a time.
  4. Don't treat when the ambient temperature is above 80-degrees. 

We hope you find this information helpful. And, if you are having a problem with an aquatic weed or plant we haven't covered here, please feel free to send us an email with photos to askapro@pondking.com, and we'll help you identify the plant and figure out how to manage it. 

We'll see y'all down at the pond!

Tags: Pond Management

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