Middle of summer, rain, and flies are everywhere. Flies are a major cause of discomfort and diseases of cattle and horses. The biting flies are especially troublesome. Other non-biting flies around the face contribute to pink eye problems as pink eye is caused by a bacteria, moraxella bovis.

First we need to understand the life cycle of a fly. They have four stages: Adult, eggs, larva (maggot) and the puparium. The adult fly will lay eggs in rotting wet organic material such as manure, rotting hay or silage and rotting compost. The eggs hatch in this medium and grow into the puparium. This is like the cocoon in which they metamorphose into an adult size fly. The pupa is a non-feeding stage which later grow into adults. There are no baby fl ies which later grow into adults; the smaller flies are just different species.

Ok, by now you have figured out the less manure and wet organic matter there is around the dairy the fewer flies there will be. Manure management is important. Fly larva has to be in a material of 40-60% moisture. Manure in a lagoon is one system where flies cannot reproduce under water. Make sure you do not let a solid cap build on top or you have just created a “fly factory” If manure is to be piled, make one large stack and try to locate a ¼ mile from the livestock as stable flies are reluctant to travel very far. The other option is to dry manure. Composting will result in heating which results in a dry material so flies will not lay eggs in it. If there is more rain, there will be more flies. A single female can lay up to 900 eggs. Normally only 2-4% make it to adults. Remember, one pound of manure can produce 500 flies!

Weed control around the building is important. Flies need a place to rest and get out of the heat. Controlling weeds near the free stall barn will keep the fly population lower in the barn. We need to understand a little bit about types of flies.

1. Horn Fly. The horn fly is a pest that came from Europe in the late 1800s. It is now populated throughout Mexico, the United States and the southern half of Canada. The fly is less than ¼ inch in length, similar in color to a house fly and has a needle like beak. This fly will have 20-40 blood sucking events each day. They spend most of their life on the back and shoulders of cattle moving to the underside during periods of hot weather. The female leaves the cow briefly to lay the eggs in a fresh undisturbed pile of manure. Eggs hatch in 24-30 hours and begin to migrate through the manure paddy. The real economic loss is from the constant biting of the cow. The constant aggravation will cause cattle to bunch, stand in water and shady areas. Substantial losses in weight gain or milk yield is experienced. The horn fl y is associated with teat end scabs on young heifers and an intramammary infection developing before the heifer calves. Treating heifers and cows is essential in controlling these pests. Treatment options include a larvacide which is put in the feed, pour-on with residual control, cattle oilers which allow for self application and placement of fly predators.

Threshold level for treatment is 200 flies per animal. Be sure to read the label if the insecticide/larvacide is to be used on lactating cows.

2. Deer and Horse flies. Horse flies are the big noisy pests which cause a real pain when they bite. Horse flies are blood feeders of both livestock and humans. Only the females bite. They lay their eggs around ponds and wet areas. The larva can live in the mud and water up to several years. Then they pupate and emerge as adults ready to complete the cycle. The flies are day time feeders. Treatment of livestock with insecticides have limited effect in keeping the pest off an animal. Traps can reduce the fly populations.

Deer flies are strong fliers capable of traveling many miles. They are found around moist areas like the shallow areas around a pond. The male deer flies are found around flowers where the female circles your head, zooms in for a bite and leaves quickly. Like the horse fly , there is limited control of this pest.

3. Face flies. Face flies are pests of cattle in pastures. They are about ¼ inch long; feeding on secretions from the eyes, nostrils and mouth of pasture cattle. They lay their eggs in fresh cow manure. They are annoying and can cause pink eye in cattle. They are strong fliers and do not like dark and shady areas.

They can be controlled with baits and repellants although have developed resistance to many insecticides. Disruption of cow pies will interrupt their reproduction cycle.

4. Stable flies. Unlike house flies, stable flies bite mainly on the lower front legs causing cattle to bunch. The stable fly is dark and about ¾ inch long. The females lay about 400 eggs in wet decaying organic matter and manure mixed with hay, feed, silage and straw. Stable flies rest in shade after feeding. Control starts with cleanliness around the dairy facilities. They can be controlled with insecticides, baits and biological control (release of other insects that lay eggs in the fl y pupae) When using insecticides one should remember only about 15% of the fl y population exists as adults. Be sure to check that the product used is approved for lactating dairy cows if used in the free stall barn. Missouri cows welcome the first frost in reducing these pests.

Source: Barry Steevens, Dairy Specialist, University of Missouri