Proper identification is called a key to aquatic weed control

Pond scum. Eeeeuww, yuck, blaah. Sounds disgusting.

Chances are your fish don't like it either, especially if such things as algae, hydrilla and other aquatic weeds restrict oxygen and create other water quality problems in farm and ranch ponds.

Aquatic plants may inhibit irrigation, access for livestock and recreational activities such as swimming and boating.

“When does an aquatic plant become a weed?” asked Billy Higgenbotham, Texas A&M University Extension wildlife and fisheries specialist, during the annual Ag Technology Conference held recently at the Texas A&M-Commerce Campus.

“When it interferes with the use of the pond, an aquatic plant becomes a weed,” Higgenbotham says.

As with most problems, the first line of defense is prevention. He says eliminating shallow water, areas less than two feet deep, helps keep aquatic weeds from getting established. A spring fertilization program also helps keep weeds in check.

Fertilizer offers several advantages, he says. “Proper fertility can double or triple the number of pounds of fish per acre a pond can maintain. Also, fertilizer darkens the water and limits aquatic plant growth.”

He cautions that fertilization should be a routine chore. “A common mistake is to fertilize in the spring while the weeds are growing. That just fertilizes the weeds. Stay on a consistent program.”

He recommends early season fertilization to avoid feeding the weeds.

Higgenbotham also recommends that farmers and ranchers treat heavily infested ponds a section at a time to prevent decaying vegetation from creating an oxygen depletion problem.

“And identify the weed and select the best control strategy for the particular pest,” he says. “Always follow label directions.”

Higgenbotham says pond managers have several options for aquatic weed control, including: chemical, biological and mechanical.

“With chemical management, make certain the product is labeled for the plant and for aquatic use,” he says. “Determine if you can live with the use restrictions imposed with each herbicide selection.”

For example, some products require a waiting period before a manager can water cattle from the pond.

“Check for availability and cost,” Higgenbotham says.

He says Karmex is a cheap, available and effective herbicide.

“It's also illegal to use in a pond. It is not labeled for aquatic use.”

Pond owners have plenty of options, however. Selection depends on the type of aquatic weed present: algae, submerged rooted plants, floating plants (true floating and emersed floating) and emersed plants.

For algae, Higgenbotham recommends copper sulfate, chelated copper sulfate, Hydrothol 191 and Reward. He says blue-green algae shows up with high temperatures and stagnant water but goes away when weather cools.

For submerged, rooted plants, he recommends: Aquathol (K, Super K), Hydrothol 191, Komen, Reward, Sonar, Aquashade, 2,4-D amine and Navigate (Chelated copper compounds may be added), and Renovate 3.

“Check the label on 2,4-D. Not all are labeled for aquatic use,” he cautions.

For true floating plants, pond managers may use Reward, 2,4-D amines (check labels), Aquathol (K and Super K), Glyphosate, Sonar, and Habitat.

“Use a surfactant,” Higgenbotham says. “Select the right one for the product used.”

He says Navigate and Amine 2,4-D, Reward, Glyphosate, Sonar, Aquathol (K and Super K), Renovate 3 and Habitat work well on rooted floating plants.

He says for something like water primrose, Glyphosate and 2,4-D may be needed.

For emersed plant control, he recommends glyphosate, Navigate and 2,4-D amine, Reward, Aquathol (K and Super K), Sonar, Renovate 3 and Habitat.

He says alligator weed was particularly tough to control until Habitat came along.

“Grasses such as sawgrass, soft stem and bulrushes may be difficult to control because of the narrow leaf surface. Glyphosate and 2,4-D, for instance, are not good on narrow leaf plants.”

Higgenbotham says Renovate 3 is a good product for some brush problems, such as willows. “It's safe to use on brush in and around ponds.”

He recommends pond owners leave large trees on dams in place. Remaining root systems may deteriorate over time and cause leaks. Smaller trees should be removed.

Grass carp offer a biological means of aquatic weed control but Higgenbotham says the process may be time-consuming and expensive. “Triploid grass carp are approved for pond weed and grass control,” he says. The triploid carp has three sets of chromosomes and is sterile. It is illegal to own diploid grass carp.

“These fish eat mostly mosses but when they consume all that, they'll eat other plants,” Higgenbotham says. “It can take a year or longer for grass carp to control aquatic weeds.”

He suggest stocking in winter or early spring or after chemical treatments have reduced vegetation.

“There are no use restrictions on water with carp,” he says,” and they provide multi-year control.”

Pond owners may face a dilemma with stocking size. Higgenbotham says the smaller fish have heartier appetites but if the pond is also home to bass and other predator fish, the small, 10-inch to 12-inch carp make good prey.

“Carp are regulated by the Texas Parks and Wildlife and growers need a permit to stock them,” he says. “TPWD does not restrict stocking size.”

He says stocking rate should be no more than seven fish per acre.

Costs include a licensing fee, $15 plus $2 per fish. Cost of the fish may vary from dealer to dealer. Triploids may not be sold off the farm but can be moved from pond to pond on the farm.

Higgenbotham says mechanical control techniques may be expensive for independent pond owners. Possibilities include seines, chains and fountains.

“Some aquatic weeds, duckweed for instance, do not like agitated water, but cost of fountains may be hard to justify for weed control.”

Drawing water down in the winter to expose vegetation to freezing temperatures also aids in weed control.

Higgenbotham says frequent mistakes in pond weed control include misidentification of the weed species, miscalculation of the pond size and volume and misapplication of chemicals.

Measuring the pond accurately is essential, he says. Owners should know both the depth and surface area of their ponds.

e-mail: [email protected]

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