If you treat all animals and there are no sources of new horn flies nearby, control through the manure should last for several weeks. Boyd Kidwell J ack Godbey hates flies. They irritate his cattle and spread pinkeye. The Boyle County, Ky., beef producer says the insects hurt calves' weight gains. Godbey is right.
Horn flies cause most of the economic loss.
These are the bloodsucking flies you see sticking to the backs and sides of cattle. Face flies, on the other hand, feed on mucus in the eyes and nose. They are annoying and spread pinkeye, but they don't hurt weight gains like horn flies do. Horn-fly control can add 12 to 20 pounds per calf. And you will help nursing cows maintain their weight.