Pasture flies thriving in hot, humid weather
- Published: Monday, July 27, 2020
COLUMBIA, Mo. – University of Missouri Extension dairy veterinarian Scott Poock says three types of flies cause economic damage and discomfort in cattle.
Typically appearing in spring, horn flies, face flies and stable flies carried over to summer this year due to hot, humid weather.
“The warmer it is, the faster the fly goes through its life cycle,” Poock says. “In a given summer, several generations can turn over as they multiply.”
Poock recommends monitoring cattle to make important management decisions. Early control reduces losses and improves overall herd health, he says. Reduced weight gain and diminished milk production result in losses. Other concerns include mastitis and pinkeye.
Adult flies are “just the tip of the iceberg,” Poock says. “When you see adults, there are many, many more at the other stages.”
Knowing where flies lay their eggs will help in their control.
Stable flies feed primarily on blood from the legs of the animal by biting with a sharp proboscis. This causes the animal to stomp its feet and swish its tail. Economic threshold is five flies per leg. After feeding, the adult female flies off to lay eggs in manure, moisture and dirt in feedlots. Keep pastures mowed and feeding sites free of residue to reduce habitats. Trim around hay bales.
Horn flies gather on the back in masses. When it is extremely hot, they travel to the belly. Female flies live most of their lives on the cow, leaving only to lay eggs in fresh manure. Economic damage occurs when there are 100-200 flies on the back of one cow. These bloodsuckers cause great discomfort. They complete their life cycle, egg to adult, in 10-20 days when it is warm.
Face flies are nonbiting flies that cluster around animals’ eyes, mouth and muzzle. They peak in July and August. These annoying flies gather around wounds. They do not stay long on the face. Instead, they spend most of their time on other objects or along waterways. This makes control more difficult.
The most danger comes from the development of highly contagious bovine pinkeye.
Insecticides are most effective in treatment of horn flies. Treatment options include dust bags, back rubbers, pour-ons, insecticide-impregnated ear tags and insect growth regulators. Topical insecticides, usually pyrethroids, may prove effective. Poock recommends rotating treatments to improve efficacy and fight resistance.
He also recommends rotating feeding grounds by moving hay rings to reduce closeness of manure piles.
As always, Poock says, follow label instructions and use safety precautions such as wearing gloves.
For more information, visit with the MU Extension livestock or dairy specialist in your area.
Writer: Linda Geist
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