This is a guide to weed control in bodies of water, such as lakes and ponds. It will cover the different methods of weed management, and then categorize different types of aquatic weeds and how best to handle them.
THE CAUSES OF WEEDS IN LAKES AND PONDS
Having plants growing in your lake or pond is generally a good thing. They provide food and oxygen for other organisms, as well as a nesting area. They can help maintain a balance of nutrients, and detoxify harmful chemicals.
A problem arises when the balance is lost, and often weeds are very effective and ruining this balance. This creates problems for both the humans that use the water and the animals that live there.
An excess of weeds can kill the fish in a body of water, or damage them in other ways. It can restrict the use of the water for recreational purposes, and create an unpleasant smell and taste.
Some reasons why a body of water may have an excess of weeds:
1) Clear water (allows for more photosynthesis)
2) Shallow water (same)
3) An excess of nutrients, particularly nitrogen and phosphorous
4) An invasion of exotic weeds, often delivered by birds
5) The present weeds may naturally be fast reproducers
HOW TO TREAT WEEDS IN LAKES IN PONDS
Here’s a list of some of the ways to handle weeds:
The best way to handle weeds is by prevention. It is much cheaper and easier to stop them from taking hold than to eliminate them once they do.
Weeds are often fed by excess nutrients in the water, and two main causes for this are fertilizer runoff and soil erosion. Also, weeds need sunlight to survive. If we can cut off their supply of nutrients or sunlight, we can make their lives very difficult.
Some ways to prevent weeds from taking told in your lake or pond:
1) Have a sediment basin upstream, to maintain the depth of water and trap out soil that would otherwise deliver nutrients.
2) Have banks that quickly drop into deep water (at a 3:1 slope or more). Most weeds live in shallow water.
3) Excluding animals, particularly livestock, from using the pond.
4) Have a grass-lined diversion ditch where fertilizers and animal wastes can be diverted.
5) Use land practices that will avoid having fertilizer and animal wastes runoff into the water.
6) Avoid adding grass clippings or leaves into the pond
7) Avoid feeding the ducks and fish
If preventative measures don’t work and weeds become a problem, here are the things you can do to help eliminate them. Remember that some of them will have negative effects on other life in the water.
1) Manually removing the weeds. In some cases, it will be possible to cut or uproot the plants. The second is best, as cutting will sometimes kill them but sometimes aid in their spread.
2) Using a shade or dye. Placing a dark sheeting over the water, or using dark dyes in the water, will cut out sunlight and starve the weeds. These methods need to be used for at least a month to be effective.
3) Pond bottom liners. Lining the bottom of the pond with plastic sheeting or a layer or mineral soil will create a barrier stopping the nutrients in the water from reaching the plants.
4) Changing water levels. Lowering the water level in the winter may expose weeds to harsh conditions, often killing them.
5) Dredging the pond. A pretty drastic step, this entails removing the whole bottom of the pond, taking out the plants and sediment, and leaving a deeper pond with a barren floor.
6) Adding animals that feed on the weeds. Sometimes adding certain fish/birds/insects/animals that feed on the problem plant will help restore balance. Know though that historically, this kind of method has sometimes led to unintended results.
7) Using herbicides. There are many herbicides available on the market today that are very effective at killing weeds in lakes and ponds. You’ll want to use these with caution, as some can be toxic, expensive, and create issues with the taste and smell of the water. The different types of herbicides will be discussed more below.
DIFFERENT TYPES OF HERBICIDES
There are 6 common forms of aquatic herbicides used today:
1) Chelated Copper. This is often used to kill algae. It can be toxic, and stays in the water for a long time. Its toxicity increases the harder the water is.
2) Endothall. These are effective, but can be toxic to fish. They shouldn’t be used in fish ponds, food grow areas, and areas where livestock frequent.
3) Glyphosate. Good for shallow, shore line weeds, and floating weeds. Loses effectiveness quickly.
4) Fluridone. One of the safest herbicides. Expensive and slow acting, but effective.
5) Diquat. This is useful for algae and submersed weeds, less effective on emergent ones. You must legally wait 2 weeks after using before the water can be consumed by humans or livestock.
6) 2, 4-D. These are good for submersed weeds. They decompose completely within 3 weeks. Toxicity increases as the pH of the water does.
When using herbicides, there will often be side effects. Even if they aren’t toxic, fish may die from suffocation, as the dead and rotting weeds take up oxygen. You must weigh whether the benefits outweigh the costs.
When using herbicides, treat less than half of the lake at a time so fish have an untreated area to move to. It’s best to apply in the spring if possible: Weeds are smaller and there’s more dissolved oxygen in the water, making lack of oxygen due to decomposition less of an issue. Also, some herbicides are less toxic at lower temperatures.
How much you’ll need to apply depends on many factors, such as the size of the body of water, the temperature and time of year, if the water flows or is stagnant, the type and density of the weeds, and the nutrients in the water. Consult the instructions that come with your herbicide, and with an expert if possible.
Some herbicides will stay in the water for less than 10 days; some may be traceable for up to 3 months after use.
TYPES OF WEEDS FOUND IN LAKES AND PONDS: A ROGUES GALLERY
Here’s a list of common weeds found in lakes and ponds, and the best methods for dealing with those kinds of weeds.
Also known as “pond scum” or “pond moss”, algae forms a greenish sludge on the surface of the water. Algae is very important to keep in check, as it will block sunlight and eat up oxygen. It is usually treated with chelated copper.
Floating weeds can be an issue because they block sunlight, starving other organisms. If weeds cover more than 1/4 of the surface area of the body of water, it’s time to take some action.
They are often effectively treated with Fluridone or Diquat.
Watermeal thrives in high phosphorous water, so keeping this low will help with prevention.
Water hyacinth is one of the fastest growing plants on the planet, so prevention or catching it early is key.
Submerged plants are often effectively treated with Fluridone or Diquat.
The presence of milfoil makes a body of water more mosquito friendly.
Emergent weeds are best treated with Glyphosate.
Phragmites are hard to fully eliminate once they take hold. Applying herbicide and then burning the roots to prevent spread has been shown to work in extreme cases.
Good luck and stay prepared!