What's Growing in my Pond??!! - Part 2

In a previous post, I described various preventive measures for aquatic vegetation control. While these measures will help prevent weed growth, they are not the answer for eliminating weed infestations that are already present. If this is the case, there are various mechanical, biological, and chemical methods available to control aquatic weeds.

Mechanical control involves physically removing the plants. This can be done by hand or with special hand-held devices designed for cutting and pulling pond vegetation, available from aquatic/fisheries suppliers. Most aquatic plants are perennial and will re-sprout if the plant is not entirely removed, including growth below the ground. For larger bodies of water, motor-driven underwater vegetation harvesters are available. This equipment is a major investment and is not a feasible option for most individuals on privately owned lakes and ponds.

In severe cases of emergent plant growth, such as cattails, complete removal with a backhoe or other equipment may be necessary. 

Biological control refers to the use of organisms to control vegetation. Biological control of aquatic vegetation has received considerable publicity recently and research is currently being conducted to determine the ability of bacteria, fungi, and insects to control aquatic plant infestations. The research has shown some potential but it is too early to tell if this type of control will work on a widespread scale.

The most widely used biological control is grass carp. Grass carp consume some algae and most submersed plants but have the potential to completely remove all underwater vegetation in a body of water. Grass carp can provide good control of pond vegetation but they have a tendency to feed on beneficial native plants before the truly troublesome weeds, such as Eurasian watermilfoil or mat-forming algae. Also, their feeding rate slows after about five years, so more fish may need to be added. Grass carp are not effective controls for duckweed or watermeal.

Private landowners in Indiana do not need a permit to introduce grass carp into their ponds but there are restrictions. First, the fish must be purchased from a holder of an aquaculture permit and the permit holder must deliver and stock the fish. Next, the land surrounding the pond or lake must be totally in private ownership. Finally, precautions must be taken to ensure the fish do not escape the stocked area, such as erecting barriers at the spillways and outflows.   

Chemical control is the most common method of aquatic plant control. A variety of chemicals are available to control different types of vegetation. When used properly, chemical controls are safe and effective. However, many are only temporary solutions and require repeated applications to prevent the vegetation from returning. When using chemical controls, read and follow all label directions. The type of chemical required depends on the type of vegetation you want to control. Many chemicals also have waiting periods on the use of water treated with the herbicides. These mostly have to do with fishing, domestic use, livestock watering, and irrigation.  

The best time to apply aquatic herbicides is late spring. Do not wait until July or August. Late summer treatments can kill fish. By that time of year, vegetation is extensive and thick and the water is warm. Killing off vegetation under these conditions seriously depletes oxygen levels in the water and can result in fish kills. If you must treat in late summer, treat only a portion of the vegetation at a time.

Additional information on aquatic weed control, including specific herbicide recommendations, can be found in Purdue Extension Publication APM-3, Identifying and Managing Aquatic Vegetation.

What's Growing in my Pond??!! - Part 1

Blue-green algae bloom (Held)

In mid- to late-spring each year, I receive a few calls on controlling pond vegetation.  However, this year these calls have been coming in about a month early (just like everything else) and with seemingly greater frequency than recent years.  Just as grass and weeds in the lawn have been thriving this spring, so has pond vegetation.  And from what I have seen so far, "thriving" is an understatement. 

Blue-green algae bloom, closeup (Held)

Proper management of pond vegetation is crucial, especially in years like this when unimpeded early, rapid growth could spell trouble for pond ecosystems later this summer.  This post will deal specifically with preventive control methods, the first step in controlling pond vegetation.  In a later post, mechanical, biological, and chemical controls will be covered.     


American pondweed (APM-3)

While it may be tempting to achieve a sterile, swimming pool effect in a pond, this is not a desirable outcome. The goal of a good aquatic plant management plan is to achieve a balance between too much vegetation and too little vegetation. Some plants, particularly native species, are highly desirable and add interest and appeal to the pond. But how is this balance achieved? The best way to achieve balance is the careful use of one or more management methods, including preventive, mechanical, biological, habitat alteration, and chemical methods.

Many pond weeds or their seeds are carried into a body of water by wind, birds, fish introduction, boat trailers, fishing, etc. Prevention starts with reducing or eliminating the causes of the spread; i.e. discouraging geese from visiting your pond, washing plant fragments off boat trailers and boats before moving to a new site, and removing plant fragments when moving fish or fish bait from one site to another.

A newly introduced weed will become a problem only if water conditions are just right. Good growing conditions usually mean the body of water is shallow or has shallow areas with good light penetration, and has an available source of nutrients (nitrogen and phosphorous) either in the water or stored in the sediment. Often nutrients enter a pond from runoff or stream flow. In addition to monitoring and reducing or eliminating nutrient and sediment sources in the watershed, the following steps can be taken to help prevent weed growth.

First, do not fertilize the pond or lake. In the Midwest, most waters are sufficiently rich in food organisms to feed large fish without being fertilized. Next, maintain a good sod and grass cover around the pond or areas that drain into the water. This will help absorb nutrients that might flow into the water as well as help control erosion. It is also thought that taller vegetation around a pond reduces the chances of Canadian geese colonizing a water site. A third step is to not apply fertilizer within 20 feet of the bank.

Livestock should not be given access to the pond except in cases of extreme heat stress. If the pond is used for livestock water, it should be fenced and the animals should be used watered using a stock tank outside the pond. Animals can add turbidity and fertility to the water and tear down the banks. It is also important to make sure run-off from feedlots or other livestock pens does not run into the pond.

Finally, a settling or retention pond or wetland area can be established to receive and settle out nutrients before the flow reaches the main body of water.

Stay tuned for Part 2.........