Observe how the plant population responds, and adjust up or down in future years. In ponds which already contain largemouth bass, it is best to stock grass carp which are at least 8" long. Stocking grass carp during late spring seems to be the most effective time of year. Plants are beginning to grow but the water temperatures and dissolved oxygen content are still favorable. Carp do have feeding preferences and will generally not control emergent vegetation species such as cattail or bulrush. Most grass carp prefer species of Hydrilla, Potamogeton, Ceratophyllum, Najas, Elodea, however carp will consume other plants as well.
Reactive approaches to controlling
algae blooms include mechanical and chemical. Removing algae by harvesting
is an expensive and time-consuming process. When applied in the spring
or fall, barley straw can be effectively used to suppress algae growth.
Some chemical algaecides are effective however, some such as copper sulfate
compounds can have negative repercussions on fish and invertebrate populations.
There are many water dyes available to prevent algae growth within ponds,
however these tend to impede light penetration to submerged plants, thus
preventing photosynthesis, reducing oxygen levels, and limiting structural
plant habitat for fish. Chemical treatments should be used as a last resort
as they treat only symptoms, not sources of algae problems.
In general, proactive approaches
to reducing nutrient inputs to your pond are the most sustainable, most
environmentally sound and in the long run, the most economical way to
control algae blooms within your pond.
Although the exact manner in which barley straw controls algae is not fully understood, barley straw placed in water begins to decay and during this process, lignins are released from the barley cell walls. Ifdissolved oxygen levels are sufficient, lignins can be oxidized via bacteria to produce humic acids and other humic substances. In the presence of sunlight, hydrogen peroxide in aquatic systems is believed to inhibit the growth of algae. Peroxides are very reactive in solution and will only last for very short periods of time. However, when high levels of dissolved oxygen and sunlight are present, the continuous decay of barley straw may provide a sufficient level of humic substances that are converted to hydrogen peroxide. The use of barley straw does not kill algae, but appears to limit the growth of new algal cells.
For barley to work properly, it must remain near the surface of the water body (e.g. within the photic zone where algal growth and reproduction occurs), and be applied prior to the onset of algae growth. In New York, this generally means that barley straw must be applied by late May or early June, though fall applications may provide some benefit the following spring. The surface waters must contain high concentrations of dissolved oxygen and have good sunlight penetration. It has also been found to be useful to keep the barley straw suspended in the photic zone using floats and some type of device to contain the straw, such as netting. Within the netting, the straw cannot be packed too tightly or it will become anoxic (low oxygen levels).