Although house flies may be of only minor direct annoyance to cattle and other animals, their potential for transmitting diseases and parasites is considerable.
Severe house fly infestations may increase bacterial counts in milk, and state inspectors routinely note fly abundance in milk rooms at dairies, according to researchers at Cornell University’s College of Agriculture and Life Sciences.
Flies also can become a serious nuisance both around the production facility and in nearby communities.
Since many dairies across the country, in addition to some feedlots, are in close proximity to rural subdivisions, ranchettes and small communities, producers are encouraged to keep house fly populations to a minimum. In addition to maintaining good relations with neighbors (and potentially regulators), this practice helps prevent the spread of diseases and parasites at the dairy or feedlot.
In general, baited jug trap catches exceeding 250 flies per week, or spot card counts of more than 100 spots per card per week, are considered high levels of activity.
A variety of cultural control practices can be used effectively to manage house flies.
The fly life cycle requires that immature flies (eggs, larvae and pupae) live in manure, moist hay, spilled silage, wet grain, etc., for 10 to 21 days. Removing and spreading fly breeding materials weekly helps to break the cycle.
Waste management is, therefore, the first line of defense in developing an effective fly management program. As the Cornell researchers emphasize: it is much easier and less costly to prevent a heavy fly buildup than to attempt to control large fly populations once they have become established.
The prime fly sources in confinement areas are animal pens, especially those housing calves. Manure and bedding should be cleaned out at least weekly.
Sometimes fly location is more important than total fly numbers on the farm. Installing and maintaining tightly closed screen doors and windows to the milk room can greatly reduce fly numbers in this sensitive area. Occasional flies that still get in can be controlled with sticky tapes, light traps or careful use of insecticides.
Flies have natural enemies commonly present in livestock barns. Beetles and mites devour fly eggs and larvae; adult flies are prone to diseases; and fly pupae are attacked by small parasitic wasps. Unnoticed and unaided by us, these natural enemies can take a heavy toll on the fly population.
Parasite populations can be conserved by using insecticides that are compatible with these important biocontrol agents. Methomyl scatter baits and pyrethrin space sprays are good examples of compatible insecticides, the Cornell University team says.
Insecticides can play an important role in integrated fly management programs. Chemical control options include space sprays, baits, larvicides, residual premise sprays and whole-animal sprays.
The researchers note that space sprays with synergized pyrethrins or a combination of dichlorvos and synergized pyrethrins provide a quick knockdown of adult flies in an enclosed air space. Scatter baits containing the insecticide methomyl are also useful for managing moderate fly populations.
A number of insecticides are labeled for use as larvicides, either for direct treatment of manure or in controlled-release formulations. Direct application of insecticides to manure and bedding should be avoided, in general, because of harmful effects on beneficial insects. The only exception is occasional spot treatment of breeding sites, heavily infested with fly larvae, that cannot be cleaned out
More tips on house fly control, and important things to avoid, are offered at http://vet.entomology.cals.cornell.edu/arthropod-identification/cow-recommendations/house-flies