Aquatic Weed Eaters

Lake weeds are almost becoming endangered species on some golf courses, in homeowners' association developments and in public parks across a wide belt of the United States. That is, they are threatened on facilities that utilize carp as weed eaters.

We don't get many cheerful stories about weed control in this day and age, but this one features a knight in shining armor. It's the grass carp, also called the triploid grass carp or white amur. This is a fish native to China and Siberia, it's the largest member of the minnow family, and it's a species that is strictly illegal unless it has been neutered so that it cannot propagate in native waters if it escapes.

Jim Broughton was already familiar and delighted with the grass carp when he arrived in Phoenix to take over the superintendent duties at Tournament Players Club Scottsdale in fall of 2002. He was happy to find the fish already stocked in the golf club's six lakes, because he knew how valuable they are. He had them at his previous courses in Texas and Oklahoma — and he loves them.

“I had the fish at Brookhaven Country Club in Dallas. I had them at a course I worked at in Oklahoma City as well,” Broughton says. That was The Greens Country Club. “I first had experience with them in 1991.”


Broughton wasn't involved in stocking the carp in the lakes of TPC Scottsdale's two 18-hole courses, but he looks out over the weed-free lakes and profusely thanks whoever did. He's part of a new generation of grounds managers who are expecting to have few weeds in their lakes, and to have this service at a low cost and with almost no chemical treatments.

“We didn't have to do any treatments,” he says of the three lakes on the Brookhaven course. “The fish kept things in good shape.”

That's even more important at TPC Scottsdale, which is a certified Audubon course and requires environmentally exacting standards, including a minimum of pesticides.

Grass carp provide an attractive alternative to chemicals, says Jeshuwa Gindiri, co-owner of H2Ology, a water facility maintenance firm in Mesa, Ariz. The company supplies the fish, through an Arkansas grower, to over 60 clients — about 90 percent of its clients use the fish.

“Most water features have them,” Gindiri says, and clients range from golf courses like TPC Scottsdale to homeowner's associations that have a pond or two. In the past he would have recommended chemical treatments. “Now we prefer stocking the white amur.”

Gindiri says the fish usually are stocked in Arizona at the rate of 25 per surface acre of lake, at a cost of $11 to $13 per fish. At that price, the fish are 10 to 12 inches long. Thus, weed control for years could cost only about $300 for a one-acre lake. He says that, in comparison, a typical chemical treatment would cost about $1,500 and have to be applied twice a year for typical Arizona weeds.


Grass carp can live for 15 years and grow to five feet in length, weighing over 40 pounds in some cases. But Gindiri points out that instead of eating more aquatic weeds as they age, the fishes' metabolism slows and they may eat less. In that case, periodic restocking, or adding fish to existing populations, may be necessary.

He recommends fish over 10 inches in length, especially if a body of water has been stocked with bass. “If you have bass in your system, they will prey on fish smaller than that,” Gindiri says. They can also die if lake water gets low on oxygen or other problems develop.

Triploid grass carp are fish that have been produced with pressure-treated fertilized eggs, which results in the retention of a third set of chromosomes instead of the normal two. That produces an infertile fish, and any grass carp that are stocked in the United States must be individually tested before release.

“We have a variety of weeds that grow throughout the system,” Gindiri says, including southern nyad, brittle nyad, widgeon grass and other submergent species such as water lilies. The grass carp eats them all.

“They've never solved the cattail problem,” Gindiri says, however. Cattails, once established, may require chemical or mechanical treatment.


Gindiri says that grass carp are a favorite of golf courses because they are environmentally friendly. He adds that the Salt River Project, which has miles of canals supplying water to central Arizona cities, uses the fish extensively to reduce weed growth.

Indeed, one of the biggest users, and the only triploid grass carp producer in the West, is the Imperial Irrigation District in Southern California. They have been raising them since 1988 and using them for aquatic weed abatement in miles of agricultural canals in Imperial County. They have even proven effective in controlling hydrilla, a devastating aquatic weed that has infested waters from Florida to California.

Imperial Irrigation District research has shown that grass carp — which have a greenish back, white abdomen and a mouth more like a bass than a true carp — are voracious feeders on sago pondweed and Eurasian watermilfoil. In 1985, some 7,800 carp were stocked into 1.5 miles of the All-American Canal, which was infested with hydrilla. Within eight weeks, all the hydrilla had been consumed.

Grass carp are becoming legal weed eaters in many states, with those state's game and fish departments becoming the licensing and oversight agencies. A big breakthrough came when California legalized the species in 2002. There has been a surge of applications for stockings on golf courses throughout the state. The Northern California Golf Association reports that some courses are actually having fish sent in by next-day air to speed weed control.

The fish can withstand cold temperatures, as evidenced by its use in Canada. Research in ponds in Alberta indicate that they will control aquatic weeds ranging from stonewort to water plantain and filamentous algae.


In Arizona, Broughton points out that management of grass carp is dead easy. He notes that they will live exclusively off lake weeds, but they can be fed grass clippings if weeds are depleted. He has scattered clippings along the shoreline and watched the fish come partway out of the water to eat them from the shore.

“They actually prefer lettuce,” Broughton says, explaining that in Dallas he would feed the fish leftover lettuce from the clubhouse restaurant. They loved it. It was particularly important to feed them something extra in the winter, when aquatic weed growth wasn't keeping up with fish appetite.

“If you have grass growing on the shoreline, they will begin eating that,” says Gindiri. He adds that some superintendents have actually had problems with keeping grass alive along the water's edge, and his company helps design specific slopes to the shoreline that make it difficult for carp to clip the turf.

A representative of Hopper-Stevens Hatcheries, a supplier in Lonoke, Ark., reports that grass carp aren't real particular about the kind of ponds they live in. They will eat catfish food if weeds aren't available. The company delivers primarily to Eastern and Midwestern states, but the carp are still illegal in Alaska, Maine, Maryland, Massachusetts, Minnesota, Montana, New Hampshire, North Dakota, Rhode Island, Vermont and Wisconsin.

Hopper-Stevens sells more than 120,000 of the triploid carp every year, and the company isn't even the biggest in Arkansas. There are a lot of weed eaters being sold, and an entire industry has developed with growers supplying haulers who work on orders from maintenance companies like H2Ology.

All Broughton knows is that the fish make his life as a golf course superintendent easier. He looks around his spotless course and sees spotless lakes, inhabited by unseen aquatic weed predators. It's a good feeling.

“I guess you just kind of take them for granted,” he says.

Don Dale and Janet Aird are freelance writers who reside in Altadena, Calif.

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