Pond Weed Control

With summer in full swing everybody wants there stock tanks to look nice.  We haven’t had as much rain as we would like but we can still pray for it. Even without rain we still see the effects of moss and algae in our stock ponds.  Treating earlier would be better, but it is not too late to think about pond management.  When we do have runoff of rains our tanks are sure to show new plant growth.  This article has some age but is still relevant for today, Dr. Michael Masser, Texas A&M AgriLife Extension Service fisheries specialist wrote a couple of years back and thought it would be important for pond owners this year.

            "Aquatic vegetation are the 'yin and yang of ponds," said Dr. Masser. "It would be nice to have some aquatic plants for esthetics and wildlife, but too many are a nightmare."  But control of moss and other aquatic plants need not be expensive or complicated, he said. Such vegetation can be controlled by mechanical, biological or chemical methods – either singly or in combination – in an integrated pest management approach.

            Pond moss and aquatic weeds can not only turn a pleasant day of fishing into a perpetual snag, they can make swimming and boating impossible too.  "Ten to 15 percent pond coverage of rooted aquatic vegetation would probably be good from a fish and wildlife standpoint, but ponds typically start out with almost none and after a very few years are almost entirely covered," he said.  There's a misconception, Masser said, that ponds and lakes can't be cleared of all rooted vegetation without critically reducing the food chain. True, plants are the beginning of any food chain, he said, but rooted vegetation tends to take over small ponds.

          Too many rooted plants not only disrupt recreational activities, but also increase sedimentation, disrupt the oxygen balance and prevent largemouth bass from finding prey fish, such as sunfish.  And also contrary to popular belief, bass do not need rooted vegetation to spawn.  "No, actually bass have to remove weeds to build their nests," Masser said. "In fact, scientific research has shown that the most productive bass and sunfish ponds are actually those that have little or no rooted aquatic vegetation and instead have green water or planktonic algae blooms."  Other research has shown that the same stringy, filamentous algae – what most would call "pond scum" – produces a more constant food supply than rooted vegetation, he said.  Counter intuitively, one of the easy ways to prevent root vegetation from taking over a pond is to fertilize, he said.

            "Note, that I said ‘prevent’ not ‘control,’" Masser said. "Proper fertilization creates green planktonic algae blooms. The algae blooms shade the pond bottom in areas over 2 or 3 feet deep and keep rooted weeds from getting started along the bottom."   Because fertilizing promotes algae growth, it also builds the food chain and enables the pond to support more fish, he noted.  An option is to use non-toxic chemical dyes to shade the pond bottom. The dyes do not promote green algae growth as does a fertilization program, however. So the treatment will promote higher fish populations.

            There are mechanical methods to control rooted vegetation, but they all require considerable industriousness on the part of the pond owner, Masser said. Weeds can be pulled or grubbed by hand or hoe. Some suppliers of mechanical cutters use a sickle wire or blade to shred the weeds. The cutters are usually hand-held and are labor-intensive. And like a home lawn, the vegetation is continually growing, so cutting has to be done again – and again. The heavy, water-laden cuttings have to be removed from the pond.  "If you like mowing your lawn, you're going to love mowing your pond," Masser said.  There's only one biological method of pond weed control in Texas: the triploid grass carp, he said.  Sometimes called the white amur, grass carp eat most submerged aquatic weeds. They cannot eat weeds that are on or project above the water surface, such cattails and lily pads.  Because it is feared the species might take over ponds and streams and crowd out game fish, only sterile, triploid grass carp are legal.

           To purchase the fish, pond owners must get a permit from the Texas Parks and Wildlife Department. The species is only legally available from certified dealers.  Though sterile, the grass carp live as long as 10 years. Typically, Masser said, they control weeds for five to seven years, but are not effective for all species of weeds.  "This type of biological control is inexpensive from the standpoint of labor and chemical costs," Masser said. "Many pond owners, after years of frustration of trying to control aquatic weeds by other means, have found grass carp to be a simple and effective answer to their problems if stocked in sufficient numbers." 

            And then there's chemical control, Masser said. The U.S. Environmental Protection Agency has registered only nine active herbicide ingredients for aquatic weed control. All have been extensively tested and are safe if properly used.  "However, many of these herbicides still have water-use restrictions of a few days to several months for uses like livestock watering, fishing, swimming and irrigation that may make them unacceptable to many pond owners," Masser said.  And there is also the risk of killing too many weeds too fast with chemical controls. Rapid decomposition of plant material in a small pond or lake can cause oxygen depletion and kill fish.

            Masser offered these guidelines when using chemical controls.

            – Treat early in the year, April or May.

            – Treat a small section of the pond – about a quarter at most – at one time.

            – Allow time for the decomposition process to complete before treating the next section.

          – Follow herbicide labels that state the entire pond must be treated at once to get effective    control.

–        Always read and follow label instructions to letter.

            For more information contact the Wise County Texas AgriLife Extension office at 940-627-3341.