Heavy populations of flies can cause stress in cattle herds and spread disease. Both stress and disease can reduce milk production and calf gain.
"Producers should start looking for the fly populations, and they need to knock those fly populations down soon," says Ron Lemenager, with Purdue Extension.
There are two main fly species that Indiana cattle producers need to worry about: the horn fly and the face fly.
The horn fly is a small, blood-sucking insect that feeds mainly on the backs, sides, shoulders and underlines of cattle. They reduce weight gain and make animals more prone to stay in the shade instead of going out in the sun to graze, Lemenager says.
Horn flies are usually easier to control than face flies because they don't travel far.
"Horn flies typically stay with the animal, only leaving to deposit eggs in manure," Lemenager says.
Face flies are known to travel more from animal to animal and from farm to farm.
"If neighbors aren't controlling face fly populations, you will get more flies bothering your herd," Lemenager says.
Non-biting face flies are about twice the size of horn flies and similar in size to houseflies.
Face flies feed on the secretions around the eyes and heads of cattle. In addition to irritating the skin, they can spread pink eye, Lemenager says.
Pink eye, also known as conjunctivitis, can rapidly spread through a herd and reduce weight gain and milk production. But the face fly spreading the Moraxella family of bacteria isn't the only contributing factor of the infection.
Lemenager said pink eye requires three basic elements: flies transmitting the bacteria, ultraviolet radiation from the sun and mechanical injury to the eye. Dust, seed heads, pollen, fescue leaves or sharp points on grass can all irritate an animal's eye. So in addition to fly control, farmers should knock down or clip pastures before turning the herd into a new pasture or paddock.
Producers have a few options for controlling flies in their herds. One option, a newer technology, is to use insecticide-impregnated ear tags. The tags contain the pyrethroid or organophosphate class of insecticides and are effective in reducing face fly populations for several months.
Lemenager recommended rotating pyrethroid and organophosphate products so flies don't build up resistance.
Farmers also can control fly populations for several weeks by using insecticides in dust bags, oilers, pour-ons and sprays. Feed-through larvacides in a mineral supplement form also have efficacy in disrupting fly life cycles.
Source: Purdue Extension