Filamentous algae is the most common aquatic weed problem in ponds. It degrades the aesthetic and recreational value of the pond. Large amounts of filamentous algae can lead to a fish kill if specific climatic conditions occur. A number of mechanical, biological, and chemical control measures are available, each with their own advantages and disadvantages.

Barley straw has received considerable attention as an algaecide based on research done in England almost 10 years ago. Results showed that barley straw prohibits the growth of many types of algae, but not all. Research in the United States has not yielded conclusively positive results. The use of barley straw to control pond algae has grown.

How barley straw may work, according to Bill Lynch, Ohio State University Extension, is the decomposition of barley straw in water produces and releases many compounds, one of which may control algae populations. The chemical compound does not eliminate existing algae cells but interferes with and prevents the growth of new algae cells.

As “old” algae cells naturally die off, few new algae cells are produced and the algae population is controlled as long as the compound is being produced. You should use dried straw, not barley hay or fresh barley. The addition of those materials actually releases nitrogen and phosphorus into the water which promotes algae growth. These fresher materials also decompose very quickly and can cause low oxygen problems in ponds.
The amount of straw to apply is based on pond surface area rather than volume of water.

It is generally recommended that about 0.025 pounds of straw be used for every square yard of pond surface area. In a one-acre pond, the amount required would be about 2-3 standard bales.

In a pond with a history of algae problems, a higher initial amount of 225 pounds per surface acre may be warranted, Lynch said.
The production of the critical compound during straw decomposition must occur in the presence of oxygenated water.  Lynch suggested each bale be broken up as much as possible so that nearly all decomposition will occur in the presence of oxygen. About 1/3 of a bale should be placed in a large, weighted permeable bag of some sort. If an intact bale is placed in the pond, only the decomposition occurring along the outside of the bale will occur in the presence of oxygen. Decomposition inside the “tight” bales will occur in the absence of oxygen and will not produce the chemical. In a one-acre pond, this will result in 6-9 loosely filled separate bags.  These bags containing loose straw should be placed around the perimeter of the pond in water no deeper than 6 feet.

Most algae production occurs in shallow water so the bulk of the control compound needs to be located there. Attaching a rope to each bag is advisable in order to retrieve the bags and replace the decomposed straw with fresh straw as needed.

Barley straw appears most effective when used to inhibit development of algae, but is apparently not effective in controlling existing algae. For this reason, barley straw should be placed in the pond in April for best results. Lynch noted as the pond water warms in May, filamentous algae growth and reproduction along the bottom can be explosive. Treatment after this period may not yield the desired control results. April treatment helps control algae growth during this critical May period.

If algae growth has not begun in your pond, apply the straw yet this week.  Using this straw with aqua shade, a coloring agent which prevents sunlight from reaching the pond bottom, should give you the desired results.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for Steve Bartels may write to him in care of this publication.