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Using barley straw to control pond algae
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Biologists call it “filamentous algae.” The folks at your local water-garden supply store probably call it “string algae” or “hair algae.” When I was a kid, we called it “pond scum,” not a technical term, but the one that best describes those stinking, unsightly mats of greenish gunk that float to the surface of small lakes and ponds during the summer. Several kinds of algae contribute to the problem, including most commonly various species of Spirogyra. At its worst, pond scum can virtually cover a pond and make fishing unpleasant if not impossible. When it decays in large quantities, the resulting depletion of dissolved oxygen in the water can kill the fish.
The most common cure for pond scum is copper sulfate applied directly to the water, but it’s definitely not ideal. Copper sulfate is toxic to fish and aquatic invertebrates, such as snails and crayfish. The repeated use of copper sulfate in a pond can lead to excessive concentrations of copper in bottom sediments. These problems led to the development and increasing popularity of Cutrine®-Plus, a chelated copper formulation that is not only more effective than copper sulfate in controlling algae, but considerably less toxic. But it has toxic properties nonetheless, is not recommended for use in backyard goldfish and koi ponds, and in some water conditions is toxic to trout. Several states, including Connecticut, restrict the use of Cutrine®-Plus.
Fortunately, there’s a possible alternative, and this one is actually healthy for the pond environment. Researchers at England’s Aquatic Plant Management group (formerly known as the Centre for Aquatic Plant Management) and elsewhere have found that barley straw, properly applied, can effectively suppress the growth of filamentous algae. Barley straw is already widely used in the British Isles for algae control, and it’s beginning to catch on in the United States, although scientists at American universities have not consistently replicated the success with barley straw achieved by their British counterparts. No one knows for sure why it works at all, but there is evidence that rotting barley straw releases oxidized lignin into the water. The lignin doesn’t kill algae, but it slows its growth and effectively keeps it at bay.
There are no precise instructions for application, as water and weather conditions vary from place to place, but here’s a start. Get your barley straw. It’s widely available in small packages at stores that sell products for backyard goldfish ponds, and those packages can also be ordered from suppliers on the Internet. If you intend to treat a larger body of water, however, you’ll want to buy straw in bulk. Bulk barley straw is most commonly available in bales that weigh about thirty to fifty pounds each. Don’t use barley hay. If you can’t find a local source, barley straw bales can be purchased online from Still Pond Farm, a Maryland farm owned by Linda Fields, an agronomist and expert in the management of ponds and small lakes, and from PondSolutions.com.
Use about 200 pounds of barley straw per surface acre. For small ponds (say, less than a quarter acre), tear the bales apart with your hands to loosen the straw. Bundle the straw from each bale into a few net bags—common garden netting is inexpensive and easy to work with, and can be tied up with string. These bundles will float at first, but as the straw decomposes they’ll probably sink, which is all right if the bundles are right below the surface or partly exposed to the air. For bundles placed in deeper water, put a float, such as a big plastic bottle with the top screwed on tightly, inside each bundle, and then anchor the bundles to the pond bottom with a cord tied to a brick-size rock, such that the bundles are suspended near the surface. Spread the bundles around the pond. If the pond is fed by a stream, put a straw bundle near the stream mouth.
The time to put out your straw bundles is early spring, several weeks before the algae begins to grow in earnest. It will take some time for the straw to begin to decompose. A bundle should last about four to six months, depending on water and climate. In places with long growing seasons, you’ll likely need to put out bundles twice a year.
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