What are some non-chemical ways to control algae in my irrigation pond?

Answer: The non-chemical solutions generally fall into one of four categories: barley straw, beneficial bacteria, aeration, and ultrasound. I don’t know if beneficial bacteria is an acceptable solution, and I have no reports as to its effectiveness or cost. Aeration may reduce the intensity of blooms, or knock back certain algae species, but I would not expect it to produce a quick or dramatic reduction in algae. Ultrasound is the most experimental of the four approaches above, and results have varied depending on the species of algae and many other factors.This brings us to barley straw, which has a long history of use for algae control and may be a good option to try. It prevents new growth more than it kills existing algae, and it is important that it applied properly. It should not be expected to cure the problem overnight. It’s available in various forms, including bags and extract. A publication from Purdue University, titled Barley Straw for Algae Control, explains the technique. It is available at www.btny.purdue.edu/pubs/apm/apm-1-w.pdf.There have been anecdotal reports of corn meal being used to control some varieties of pond algae, including one from Howard Garrett, a well-known author of gardening books. According to Garrett:”For floating paint-like and filamentous algae in water, use cornmeal at 5 pounds per 1,000 square feet or 150-200 pounds per surface acre. The cellulose in the cornmeal helps to tie up the excess phosphorous in water, balances the water chemistry and thus kills off the algae. The organic carbon in the cornmeal enables the beneficial bacteria in the water to flourish at the expense of the algae. Then the decomposing algae provide a source of carbon for the bacteria. One or two treatments is usually enough to control the algae for several months.”Your algae problem may also need to be addressed at the filtration end of the irrigation system. A good sand media filter will remove most algae and other biological contamination.It is important to note that algae thrive on nitrogen and phosphorus, so you should to try to limit inputs of those chemicals into the water from the surrounding land/water. Otherwise, you’re simply creating ideal conditions for algae?warm, shallow water and lots of N and P. Livestock should be kept out of the pond, and their presence minimized in the watershed and fields surrounding the pond.