Craig Wood, University of Kentucky

Fly control should be initiated in late spring or late fall. Weather that is hot and dry or cold and wet produces fewer flies. Warm, wet weather means more flies. Cool, wet weather will delay fly life cycles.

Adult flies live for about two to three weeks in warmer weather and longer during cooler weather. Stable flies develop so rapidly that they can complete several generations each summer.

Numerous repellent sprays, wipe-ons, roll-ons, salves, lotions, and slow release insecticidal devices are available for on-horse fly control. There are many brands of fly repellents, but basically they can be divided into those containing:

1. natural pyrethrins (usually with the synergist piperonyl butoxide), which are derived from plants; or
2. synthetic chemical formulations that often include pyrethrins.

Those that use natural pyrethrins may give nearly 100 percent repellency for hours. Some combination products may claim to work for several days or more after applying them to the horse.

Horse wearing fly mask

Fly repellents used on horses may be oil-based, alcohol-based, or water-based. Most are available either in ready-to-use or concentrated form. Roll-on repellents are available for use on the horse's face and near open wounds. Repellent ointments keep flies away from cuts and other injuries as well. Some the repellents on the market also contain sunscreen and aloe, lanolin, and other emollients to condition and moisturize the skin and coat. Sunscreen fly repellents will help to prevent sunburn on horses with mostly white heads. Fly sheets are good for body coverage, but they don't protect the forelegs from biting flies. Fly masks provide excellent nonchemical fly control for a horse's face and ears but need to be removed at night.

Natural, noninsecticidal repellents are available. Many people prefer to use a natural product. Typically, natural repellents are less effective but do offer other advantages. Aside from the appeal of not using harsh chemicals, a natural repellent can be effective in a light fly season or at the beginning and end of the season. However, you should consider using a stronger insecticidal formula during the height of fly season.

An integrated pest management program provides the best opportunity for an effective external parasite control program.

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