Green Algae Control Lake Management

Vegetation Identification - Floating Plants

Floating Plants account for some of the most prolific and invasive plant species. Giant Salvinia, Water Hyacinth and Water Lettuce are three of the most troubling Non-Native Invasive species of plants to ever be introduced to Texas waters. There are also some Native plants that can rapidly cover a pond, such as Duckweed and Watermeal.
Floating plants have an advantage over other plants in that they are the first to recieve sunlight. Once a stand of vegetation is started on a lake it can shade out everything below it and have less competetion for nutrients. If an infestation gets to the point that it covers the entire surface of a pond it can prevent the exchange of oxygen and lead to serious problems for your fish.
Lake with Water Hyacinth
Here you can see a lake that has atleast 20+ acres of solid Waterr Hyacinth. This vegetation can double the size of a stand in as little as 14 days. So even if this lake took a few years to reach this level of growth it could be completely covered in a matter of weeks. A lake in this condition offers little recreational value.

For more information on Water Hyacinth from the USDA

Common Floating Aquatic Plants

We've already mentioned the severity of Giant Salvinia and Water Hyacinth, however Giant Salvinia is not extreamely common at this time. Water Hyacinth is very common along the Gulf Coast and in regions that are not prone to winter freezes. The Duckweeds though, are probably the most common floating plants found in Texas. There are about 7 different species of Duckweed and several species are often found in one location along with Watermeal, which looks like duckweed in miniature.
Duckweeds are small, single, circular to oblong leaves that float on the surface. At least a single root can be found hanging below each frond or leaf and certain species will have multiple roots on a single frond. Duckweeds and Watermeal are the smallest flowing plants on the planet. Blooms are not visable to the naked eye.
Azolla or Mosquito Fern is another common plant in this area. At first glance Azolla may apear to be Duckweed with a red color, but upon close inspection you will see a leaf structure that is very different from Duckweed. Azolla is a true Fern and it's leaves somewhat resemble that of common ferns, under magnifiaction it may appear as multiple diamonds linked together.
Azolla, Duckweed and Watermeal
Picture: Azolla, Duckweed and Watermeal under magnificaiton. The Azolla is the largest and has a redish color along it's edges. Duckweed is the next largest plant, green and somewhat circular. Watermeal is the smallest. Duckweed is usually about 1/16" across the leaf.

Control of Floating Aquatic Plants

Floating plants are somewhat easier to treat than the other groups. Because floating plants are mostly exposed they are susceptable to topical treatments. Contact herbicides can produce good results on most species but repeat applications will be required to provide season long results. Contact Herbicides are almost always used on Water Hyacinth, and Water Lettuce as they are much cheaper and systemic products are not often practical on these species. The Duckweeds, Watermeal and Azolla can be controlled with a systemic herbicide, most commonly a fluridone based chemical. Fluridone products can provide season long results often with one application, however there are a tremendous amount of varialbles to be concidered inorder to have a successful treatment. To skip ahead to the section on Sonar (41.7% Fluridone Herbicide)

Mechanical meathods are not very effective on floating plants as they are prone to move with wind and water curents. Additionally the small size of plants such as Watermeal make physical removal difficult.
Grass Carp are a consideration for Duckweeds as they are a preffered food, however additional measures are usually required to provide the desired results.

Aquatic Plants Factsheets