Pond owners should get a jump on aquatic weed control

Watershield grows along the edge of a farm pond. - Submitted photo
Watershield grows along the edge of a farm pond. - Submitted photo

PINE BLUFF -- With warmer temperatures, farm pond owners can now start getting back into the rhythm of active pond management Scott Jones, small impoundment Extension specialist at the University of Arkansas at Pine Bluff, said.

"This year, pond owners should prepare for an early emergence of algae and other weeds due to a warm February and the ice and snowfall over the winter," he said. "Algae is already growing in most parts of the state."

Jones said there are hundreds of thousands of species of algae. In the pond environment, there are three primary forms of algae -- planktonic, filamentous and macrophytic.

Planktonic algae

"Planktonic algae include beneficial green algae and diatoms that produce oxygen and feed zooplankton, which are extremely important diet components of young and filter-feeding adult fishes. This type of algae makes water appear a transparent to opaque green."

Planktonic algae blooms are necessary for good fish production, but they can become troublesome if they grow too dense, Jones said. A general rule of thumb is to maintain 18 to 36 inches of visibility in the water through nutrient management.

Jones said an algae bloom's species composition changes throughout the year based on environmental conditions.

"In the hottest months, photosynthetic cyanobacteria commonly known as 'blue-green algae' can become dominant," he said. "These species are typically involved in 'harmful algal blooms,' which are blooms that cause negative impacts to other organisms. This type of algae is not consumed by zooplankton at the detriment of the pond food chain. Many blue-green algae are capable of producing toxins that can irritate animals and humans and even kill when consumed at high doses."

Nutrient sequestration using flocculants such as aluminum sulfate or commercially-available products such as Phoslock, Phosclear or similar products are usually required to strip nutrients from ponds experiencing harmful algae blooms, he said.

Filamentous algae

Filamentous algae are single-celled species that stick together to form webs or filaments. These algae begin growing on the bottom of a pond and float to the surface once mature to create unsightly and burdensome mats.

"A combination of herbicide, aquatic dye, nutrient sequestration and even tilapia can help manage filamentous algae issues," Jones. "Landowners should be aware that herbicide treatments to filamentous algae are usually only temporarily effective. The algae are cleared away in days, but then reemerge within two to three weeks just as bad as or even worse than before."

Jones said this type of algae is one of the most difficult aquatic weeds to control. Herbicides alone will not provide long-term control. He recommends an effective herbicide that contains copper sulfate, followed by nutrient sequestration with a flocculant one to two weeks after herbicide treatment. Landowners should continue these two steps until plants are under control.

Macrophytic algae

Macrophytic or "macro" algae are species that form networks or structures that resemble vascular plants (those with xylem and phloem) but lack the interconnecting vascular tissues, Jones said.

"Chara algae, for example, look extremely similar to the common vascular aquatic plant coontail," he said. "Macro algae grow on the pond bottom and form clumps or meadows usually around one to two feet tall. They are occasionally problematic and can be treated with copper-sulfate based herbicides. Grass carp are an effective control measure against this kind of algae."

Controlling weeds early in the spring is important for several reasons, Jones said. If weed infestations are caught when small, control is easier and cheaper. Also, dissolved oxygen problems can result if herbicides are used to control weeds during the summer, so treatment needs to occur before the water gets hot.

"Effective control measures vary widely among different types of weeds, and weed control begins with correct plant identification," he said. "University of Arkansas Cooperative Extension Service county agents, Arkansas Game and Fish Commission fisheries biologists and UAPB aquaculture and fisheries specialists can help you identify your plants and select effective, safe control measures."

For more information on pond maintenance, contact Jones at [email protected] or call 870-575-8185.

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