Algae growth during the summer season in farm ponds can pose a number of problems. The algae that grows in ponds used for irrigation can clog pumps, block filters, cause odor problems, and is generally considered to be very unsightly. These algae blooms seem to be more severe in ponds that have high levels of nutrients which can be associated with runoff from production fields. 

The control of algae with mechanical or chemical means can be costly and ineffective. The use of some chemicals may limit or restrict the use of the water for irrigation. Chemical control also often removes the higher plants as well as the algae. Once the herbicide is gone, the algae often recolonizes the pond fairly quickly because there is no competition from the higher plants. Thus, over time the algae problem can get worse if this pattern is continued. 

For a number of years barley straw has been recommended for use in ponds in this area, yet there has not been a lot of scientific data to back up these recommendations. The Center for Aquatic Plant Management in the United Kingdom has spearheaded the development of this method of algae control. 

The straw does not kill the algae that is already present, rather it prevents the growth of new algal cells, similar to a pre-emergent herbicide. The anti-algal activity is only produced when the straw is rotting in a well oxygenated environment. 

The amount of straw needed is based on the surface area of the pond. The volume of water seems to make no difference in the performance of the straw. As a rule of thumb .5 - 1.5 oz. of barley straw per 10 square feet of surface area will provide good activity against the algae. Higher rates have been shown to provide better algae control if the problem is severe. However, too much straw can deoxygenate the water. It is best if the straw is applied loose so that water can move freely through it. A cage similar to a crab trap works nicely. Floats should be attached to the cage to keep them at the surface for maximum efficiency. It is also better to use multiple cages. The more points that the barley straw extract can emanate from, the better the control. 

As far as timing goes, it would be best to apply the straw in the fall or early spring. This will give the straw a chance to rot and get ahead of the spring/summer algae blooms that cause most of the problems for irrigation ponds. When barley straw is applied to a pond it generally takes 6-8 weeks for the straw to become effective at water temperatures below 50 F. When the water temperatures are 68 F or above it only takes 1-2 weeks for the treatment to become effective. Once active the straw will remain effective for about six months. 

To this point there have been no negative side effects recorded. There have, however, been observations of increased invertebrate populations and improvement of gill development in fish from ponds where barley straw is applied.
 
 This was a brief summary of a study done by the The Center for Aquatic Plant Management in the United Kingdom. Click here to view the complete 15 page study with pictures and diagrams in PDF format.

Barley straw study