In recent years, there has been increasing popularity in the use of barley straw to control algae populations in ponds. First reported in scientific journals in the early 1990's, it was discovered that during the decomposition process, barley straw releases small quantities of algistatic chemicals which impact algae growth. The primary suspected compound is Hydrogen Peroxide. The process has been reported to be effective with most forms of filamentous algae as well as blue-greene algae.
How to Apply
The decomposition process must be done in the presence of oxygen (aerobic process), therefore it is most effective if the barley straw is placed in the pond in a loose manner which maximizes exposure to oxygen. Application is best done by placing loose barley straw in a mesh bag or even sections of discarded stockings. The treatment is most effective if flowing water passes through the straw as it decomposes. If your pond has moving water, place the mesh bags in that area. If not, use floats to keep the bag near the pond's surface and normal wind action will move the straw-filled bag around the pond.
Rate of Application
When determining how much barley straw to apply, the volume of water in the pond is less important than the surface area, as only treatment of the top layer of water is required. Recommended applications vary, with rates ranging from 1 pond of straw per 100-3600 square feet. Since the treatment is not toxic, a good rule of thumb would be to use 1 pound per 100-200 square feet of pond surface. On larger ponds, rates of 2 bales per acre may be required for effective algae control.
Timing of Application
It is important to understand that the chemicals released by the barley straw do not kill existing algae, but rather work by inhibiting new growth. Therefore, it is important that treatments begin early in the season before algae has a chance to establish in your pond. Begin treatments in March with the introduction of the initial straw materials, and replace in early July (or sooner if you observe algae growth increasing). Initially, the barley straw may take several weeks to become active due to cold water temperature. In some cases, the effects of the barley straw have been reported to be effective as long as 6 months after application, but a decline in the algae control benefits is often noted after 3 months.
Types of Straw
While there has been limited research on the subject, all experiences to date have shown that barley straw exhibits the type of benefits sought for algae control best. While wheat and other straws have shown some successes in algae control, they work much slower and for a shorter period of time. Under no circumstances should hay be used as it increases algae growth due to rapid decomposition and a tendency towards an anaerobic condition.
Check with your local garden center or farm supply center for the availability of barley straw in your area.