D. Allen Pattillo
Iowa State University Extension & Outreach
The warm, early spring weather has prompted the growth of vegetation across Iowa’s nutrient rich soils – and soon it will encourage growth in the nutrient-rich waters of Iowa ponds. During this time of year, known as the spring turnover, oxygen and nutrients get distributed throughout pond water, the sun gets stronger and the first algae begin to grow.
Pond owners need to know that wherever there is sunlight, water and nutrients, there will be some sort of plant growing. Effective management involves manipulating one or more of these elements to reduce or eliminate aquatic plants.
Aquatic plants are categorized into four major categories that occupy slightly different habitats – algae, floating plants, emergent plants and submersed plants. Each of these plant categories requires a slightly different control management strategy.
Those controls are biological, mechanical, cultural or chemical removal methods.
- Biological control typically involves an animal, like grass carp, that feeds on aquatic plants to control submerged plants. In Iowa, grass carp are typically stocked at four to eight 8-10 inch grass carp per surface acre, depending on the amount and type of vegetation present.
- Mechanical control methods mean using tools like rakes and shovels to remove aquatic plants. This method may be most appropriate in very small ponds because they require a lot of human labor to maintain.
- Cultural methods include water draw-downs and partial pond drying. These are usually the most effective form of control because they prevent aquatic plants from getting started, although they may be labor intensive initially. Creating steep sided ponds that reach a depth of three feet or greater relatively close to shore reduces the ability of rooted plants to establish because of light limitations. Please note that these areas can be hazards to children and those who cannot swim. Installing rip-rap on the bank of the pond will reduce the rooting ability of plants on the shore, although this may cause problems for wildlife like turtles. Aeration may also provide some temporary relief from aquatic plants by making phosphorus, a major plant nutrient, unavailable for plant uptake. Pond dredging may be necessary every 20-30 years to reduce sediment nutrient loads, which directly contribute to the fertility and plant biomass in a pond.
- Chemical control methods are generally the last resort for pond-owners. This treatment method is plant species specific, can be quite expensive, has variable results, may be toxic to fish and other aquatic organisms, and requires Category 5 Aquatic Pest Control certification to apply. In order for these methods to be effective, pond-owners should start implementing these management strategies in the winter and early spring to get ahead of plant growth and prevent establishment.
Pond owners and those thinking of building ponds will find valuable information in the publications Building Quality Ponds and Aquatic Plant Management, both available as free downloadable PDFs from the ISU Extension and Outreach Online Store. For more in-depth information, I recommend the Aquatic Pest Control Manual, available for purchase through the Online Store.
For more information on pond management, contact the Extension Fisheries program at www.nrem.iastate.edu/fisheries/