Q: Can I treat my manure pile with anything to help reduce the amount of flies at my barn?
A: Your manure pile may be producing flies, depending on temperature, moisture content, and how long before it is spread. However, flies are likely to be coming from other sources, and spraying the manure pile alone may not produce the desired results. Breeding sites can be located by searching your premise for places where maggots are actively developing, including soiled bedding, feed debris, areas around waterers, etc. Once located, sources can be eliminated by scraping and spreading the manure, and by preventing manure accumulations from recurring.
If stall "pickings" must be piled, then consider composting as an alternative to spraying. For maggot control, you will need to create a hot, actively composting pile, where temperatures are greater than 140° F. Fresh manure will need to be mixed with another source of carbon, such as straw or sawdust. If space permits, create a new pile each week, and turn all piles weekly to maintain aerobic conditions.
By Roger Moon, PhD, University of Minnesota