Weeds Under Water

— Written By Mitch Williams and last updated by
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What do you consider a weed? Often our first thought goes to the dandelion in the lawn, grasses in the garden, or morning glories in crop fields. Really though, a weed is any plant growing where it is not wanted. One place most of us do not think about when imagining weeds is in a pond, unless of course you are a pond owner.

Aquatic weeds, those found in ponds, are a big concern for almost anyone who owns or lives near a pond. When you consider that there are over 1,000 ponds in Lee County, aquatic weeds may in fact be the first weeds that come to mind for several of you reading. Managing aquatic weeds is something that should begin before you ever have a problem, and will vary depending on what you intend to use the pond for. Just like in any situation, not all plants in a pond are bad. Some can be beneficial for fish and wildlife, and the presence of algae is even essential for fish to survive. On the other hand, algae can get out of control, causing blooms and die-offs that can kill fish, and other plants may choke out native vegetation and completely take over.

As I mentioned, management of aquatic weeds should begin before you have a problem. Monitor your pond for weeds and try to catch new weed pests before they become a problem. Weeds often become a problem in ponds when too many nutrients are entering the system. This can occur from fertilizer runoff from your yard or pasture, animals getting into the pond, or yard waste entering the pond. If you mow around your pond, remember to leave a buffer area, and not mow up to the edge. When fertilizing, avoid fertilizing up to the edge of the pond. Native sedges and rushes thrive in wet soils, and when planted around ponds can do an excellent job of capturing nutrients before they reach your surface water. If you have livestock, consider installing a drinker for them, and fencing out ponds to keep manure out of surface waters.

Once you have a weed problem, be prepared to use a variety of tactics to regain control of your pond. Aquatic weeds can be controlled biologically, mechanically, or chemically. One common biological control for aquatic weeds is the use of triploid grass carp. Grass carp are sterile, so they will not reproduce and become invasive. If stocking a large pond or lake, a permit may be required before stocking grass carp, but is not required for most small ponds. Initial stocking cost can be expensive, but grass carp have a lifespan of about 10 years, so control over the life of the fish is much cheaper than chemical options.

Mechanical control is sometimes an option with aquatic weeds. Small areas can be raked out, and most of these weeds will die once they are removed from water. Unfortunately, many aquatic weeds reproduce from fragments, meaning any small pieces of the weeds which are broken off but not removed by raking may be able to regrow and even cause the weed to spread to other parts of the pond. Chemical control is sometimes the only option.

When considering what control option is best for you, it is important to identify the weed you have. Grass carp do not eat all aquatic weeds, and aquatic herbicides should be selected based on the weeds you have. For help identifying weeds, there are many resources available online, including Aquatic Weed Management. If you are in doubt about what weeds you have or what herbicides you can use, bring a sample to the McSwain Center at the N.C. Cooperative Extension of Lee County. I would be happy to help identify your weed, help you choose a herbicide, and help you understand the label. As with any pesticide, always read the entire label and be sure you understand it. If you are ever uncomfortable applying pesticides yourself, contact a professional.

Mitch Williams is the Agriculture Agent – Field Crops, Livestock, and Pesticide Coordinator for North Carolina Cooperative Extension in Lee County.