Got Weeds? Get Carp

Tranquil, scenic ponds on your property can quickly become unsightly when they're clogged with weeds.

Before you turn to herbicides or mechanical methods to remove them, however, consider using a more natural method - grass carp.

Grass carp are herbivorous, freshwater fish that love eating pond weeds, especially hydrilla. They've been gaining popularity in recent years as various municipalities and states have used them to effectively control weeds in lakes and ponds.

At least 35 states now allow the use of carp, though most stipulate that property owners notify their local department of wildlife before they do so. Most states also require that owners use only triploid carp - a sterilized variety created to stem concerns about the foreign species' impact on native ecosystems.

Once approved, owners can usually purchase carp at local fisheries. The carp can be expensive - about $10 a piece for the larger, triploid carp - but they last several years and are often more effective than other methods.

The best time to stock carp is in the late spring, when waters are cooler and weeds have just begun to grow for the season. Grass carp are easier to transport in the cooler months, and stocking carp in warm, summer waters can be hazardous to the fish's health due to lower oxygen levels in the water.

Experts recommend stocking the fish incrementally. Stocking too many carp can deplete all the vegetation in a pond, which causes excessive algae blooms. But stocking too few carp will produce lackluster results when it comes to weed control.

Property owners should stock a small amount to begin with, experts say, and then increase in two-year intervals, if needed. Grass carp are often ineffective in their first season, but they usually produce noticeable results by their second season. For ponds with low plant density, plan on five fish per acre to start off; for medium density, 10 per acre; and 15 per acre for high density.

When stocking a pond with grass carp, it's important to block off any canals and culverts with screens or gates to prevent escape of the carp. Larger carp should be used if weeds are few and far between and in cases where predator fish might have access to the pond. Smaller carp thrive in ponds with dense, protective weed cover.

Once a pond is stocked with carp, it can be difficult to remove the fish. The most effective methods are usually to either drain the pond or use a fish toxicant to kill the

carp.

SOURCES

http://warnell.forestry.uga.edu/warnell/service/library/index.php3?docID=185

http://www.dec.ny.gov/outdoor/7973.html