Per the manufacturers label for Repel-X pE Emulsifiable Fly Spray:  To protect horses from Horn Flies, House Flies, Gnats and Mosquitoes apply at a 1 to 7 dilution. Each pint of concentrate makes a gallon of finished spray. Repeat application every 3 or 4 days but not more than one treatment a day. Where Horse Flies, Deer Flies (Tabanids), Stable Flies, Ticks, or Deer Ticks, that may transmit Lyme Disease, are a problem, apply 1 to 4 dilution and repeat as often as needed.