Just as longer days mark the beginning of summer, so does the arrival of increased number of flies in feedlots.

Stable flies and house flies are the most common pests of cattle in feedlots. Of the two species, stable flies cause the greatest economic loss. Left unchecked, these pests reduced sale weight in feeder cattle by 20 pounds in controlled research trials. Most of that lost performance results from the indirect effects of flies, such as bunching and increased heat stress. In addition, increased fly populations can lead to poorer relations between feedlots and their neighbors.

Sanitation and chemical control

Controlling feedlot flies starts with sanitation. Stable flies breed in mixtures of spilled feed and manure, especially around feeding aprons, under feed bunks, feed storage areas, and under fences. Removing feed and manure from these areas promptly deprives the flies of potential breeding areas, which in turns helps prevent explosive increases in fly populations.

Chemical controls can be a part of a fly control plan in conjunction with sanitation efforts. Stable flies prefer to feed on the front legs of cattle, meaning that getting good spray coverage for this pest is difficult. Premise sprays may be more effective, especially in areas where the flies rest. Stable flies rest on the shady sides of buildings, feedbunks, and on vegetation. During the day flies will also rest in trees used as windbreaks; spraying along the edges of the windbreak may be as effective as treating the pens themselves.

Biological control strategy

Biological control using parasitic wasps is another option to consider. Parasitic wasps lay eggs in the pupae of flies. These wasps can reduce the number of adult flies in a feedlot and delay the peak in population if the parasite population is high enough during the fly breeding season. This strategy is not a “quick fix”, but rather a part of a longer-term strategy to reduce fly pressure.

One of the key factors to successfully implementing a biological control strategy is to find a reputable supplier who can provide the right species and manage the releases for optimal results. Periodic releases throughout the fly season are more effective than one massive release.

Sanitation is still critical when implementing a biological control program. If the fly breeding areas are too large, the flies will simply outbreed the parasites resulting in little to no effect on cattle performance or overall fly populations. Reducing the number of breeding areas will concentrate the flies and help make the parasite control more effective. It is important to remember not to use chemical control in all the breeding areas when using parasitic wasps. The parasite requires live pupae to reproduce.