Winning the weed wars

Aquatic vegetation can benefit fish populations, but it can also hinder anglers.

The time when aquatic vegetation starts growing in ponds is about a month off. Because prevention is usually more effective and less expensive than cure, it’s a good time to be thinking about vegetation management.

A common spring occurrence in Magnolia state ponds is an algae with the less-than-endearing name “pond scum.” Starting in April in South Mississippi and May in Central and North Mississippi, a lot of ponds become fringed with floating algae.

Algae mats might grow out just a few feet from shore, or they can grow out 10 or 12 feet and make fishing from the bank difficult or impossible.

The culprit is filamentous algae that grows on the bottom of shallow water. As the days lengthen, solar energy increases and the water warms, the plants multiply and produce more oxygen and carbon dioxide. The oxygen and carbon dioxide produced by the algae are trapped under the thickening mat, floating the mat to the surface.

Instant pond scum.

The bad news is that it is unsightly, it is a nuisance and there really isn’t anything you can do about it.

More bad news: If your pond had pond scum last year — and especially if you had pond scum for the last several years — you will probably see it this year.

The good news is that if you can live with it, don’t worry about it. It will go away in a couple weeks.

If you would rather not live with it, stocking two or three triploid grass carp per acre might prevent it.

Submersed aquatic vegetation can be a significant problem and, unlike pond scum, they don’t go away.

Aquatic plants can be a boon to large and deep lakes and reservoirs, increasing production of aquatic invertebrates that provide food for sunfish and a wide variety of forage fish bass and crappie eat, and they concentrate fish for anglers.

Although non-native plants like hydrilla and Eurasian water milfoil can be problematic because of their low light requirements and growth form, the greater depths of most lakes and reservoirs prevents extensive growths of most aquatic plants.

Ponds, however, are supposed to be shallow and, therefore, are highly vulnerable to extensive growth of aquatic vegetation.

But “shallow” requires clarification. A well-built pond will have shorelines that steeply slope to a depth of about 3 feet, and most of the pond should be at least 5 to 6 feet deep.

These conditions minimize the area where sunlight reaches to the bottom of the pond, suppressing extensive plant growth.

Note: The best way to prevent aquatic vegetation problems is to build the pond correctly.

But not all ponds were properly built, and deepening a pond and steepening the shoreline might not be an option.

Short of renovating the pond, the most economical and longest-lasting treatment for excess aquatic vegetation in ponds is stocking triploid grass carp.

Floating algal mats usually disappear in three or four weeks after first appearing.

If your pond had too many weeds last year, it will have too much vegetation this year, and now is a perfect time to stock triploid grass carp. The grass carp will graze on the succulent new plants as they regrow.

Because the amount of vegetation is lowest in the spring, fewer grass carp will be needed to suppress the plants now than in the summer when there is a lot of plant biomass established. And the fish are much more easily handled and have better survival when stocked into cool water.

A word of caution to help you spend your money wisely: Triploid grass carp will control most submersed aquatic weed problems but not all. Check out

If you are not sure what plant or plants are causing the problem, look at to identify your plants. If still unsure, visit your county extension agent.

Ten grass carp per vegetated acre will control most pond weed problems if you stock in the spring. If the pond has largemouth bass, stock triploid grass carp that are at least 12 inches long to prevent your weed eaters from becoming bass food.

A lists of suppliers of triploid grass carp can be obtained from your County Extension office or go online to Mississippi State University Extension at

Weed problems also can be controlled by fertilization and chemical herbicides. Fertilization works by creating an algae bloom that reduces light reaching the bottom and suppresses rooted aquatic plants.

And fertilization can be a good solution because it often increases fish production.

But fertilization is expensive, has to be repeated throughout the April-through-October growing season, and can make your weed problem worse if not done properly.

Chemical treatments can be the quickest fix to weed problems, but use of aquatic herbicides is expensive, usually requires repeat herbicide applications and can cause water quality problems if you have a lot of the pond infested with aquatic plants.

So triploid grass carp are a simple, inexpensive fix with long-lasting benefits if your weeds are among those that grass carp eat. Should grass carp not reduce your weed problem to a satisfactory level, it is easy to stock a few more per acre next year.

About Hal Schramm 182 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.

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