Summer, Fall Cattle Flies: Pesky But Treatable

FAYETTEVILLE, ARK.
   Pasture flies that are irritating to cattle and painful to producers’ account ledgers have been abundant this year, said Kelly Loftin, extension entomologist with the University of Arkansas Division of Agriculture.
   “We’re talking about face flies and horn flies,” Loftin said. “We call them pasture flies because they breed only in fresh cattle feces that are less than 10 minutes old.”
   Though face flies seldom cause infestation problems in central or southern Arkansas, the state had substantial face fly populations between late May and early June.
   “Face flies are the ones you see feeding around the eyes and nostrils of cattle,” Loftin said. “They can potentially transmit pinkeye to your livestock.”
   Horn flies create other problems for cattle and cattle producers.
   “Horn flies are the most economically important arthropod pest in cattle” for the damage they inflict, Loftin said.
   “Significant reduction in calf weaning weights is well documented,” said Tom Troxel, associate director of Animal Science with the division. “This loss is related to a decline in milk production as a result of horn fly feeding or annoyance.
   “Studies have shown that effective horn fly management can result in a 15- to 30-pound increase in weight in stocker calves during the growing season,” he said. “In today’s market, that’s $15 to $30 per head.”
   University of Arkansas researchers noted a 17-pound reduction in calf weaning weights for every 100 flies feeding on the cow, Troxel said. That comes out to a $20 loss in today’s market.
   Horn flies have long been implicated in the spread of summer mastitis in some cows. The flies can also spread a nematode that creates “an exposed lesion between the navel and brisket,” Loftin said. “The nematode occurs throughout the U.S. but is more prevalent in the west and southwest U.S.”
   Insecticide treatment is advised when there are more than 10 flies per cow. Insecticide-impregnated ear tags also aid in warding off pasture flies, especially when each ear is tagged.
   “Producers have also had good luck using selftreatment or back-rubber devices that apply an oil-insecticide solution to the back and face of animals when they pass under the device on their way to food or water.”
   Loftin said livestock owners can plan on dealing with horn flies every year.
   “Horn flies are blood-feeding flies,” he said. “Their numbers peak in June, decline and then re-emerge in the fall.”
   However, some monitored herds have not seen the usual decline in horn flies in late summer.
   “We saw some animals with more than 1,000 horn flies per side,” Loftin said. “Fortunately, not all producers have experienced this degree of infestation on their cattle.”
   Horn fly control is recommended when there are 200 flies per head. Control methods include walk-through traps with no insecticides, backrubbers and dust bags, insecticide sprays, pour-on insecticides, insecticide-impregnated ear tags and feed-through insecticides that kill or regulate larvae.
   “Producers can expect horn fly populations to begin rising for the fall population peak,” Loftin said. Δ