Even though it's springtime and dog days of summer still seem light years away, it's never too early to get a jump-start on the war against summer flies. There's even a new weapon to add to your arsenal, and it works best starting now.
Before you have to drag out the sprays, smelly traps and fly masks, consider using some feed supplements that "pass through" your horse to help control flies the moment the weather warms up. These feed-through insecticides are made by several companies that also sell basic fly sprays, and can be a good way to keep the fly population down around your barn.
Dress this stuff on your horse's grain and it will do its job in his manure, killing adult flies and larvae on contact. The active ingredient is usually a chemical called tetrachlorvinphos, which destroys an insect's nervous system.
Tetrachlorvinphos inhibits cholinesterase, which is essential for transmission of nerve impulses. It's an organophosphate pesticide that is chemically related to the nerve gasses developed during World War II. There is some debate over whether it is absorbed by the horse or passes through quickly enough to not get into the horse's bloodstream. Signs of absorption in a horse would include abdominal pain, lethargy, sweating, tearing, and excessive salivation.
This product is designed to pass through the digestive system too quickly to be absorbed. Regardless, it is a neurotoxin and, three years ago, the EPA published a notice advising horse owners to consult veterinarians if using these feed-through pesticides on old or debilitated horses, or pregnant or nursing animals.
Farnam's Equitrol keeps larvae from hatching via its main ingredient, Rabon (tetrachlorvinphos). It takes one ounce of Farnam's Equitrol daily to do the trick (you can buy 3.75 pounds for $17, up to 20 pounds for $65). Crystalx also offers Rabon in a block supplement called Rolyx Pro, which adds additional protein supplementation. The company claims the block availability offers more consistent intake, and this would save you the time of feeding it.
Something New
A new component in feed-through options is IGR, or Insect Growth Regulator. It doesn't affect adult flies, but prevents fly larvae from developing into biting adults. The active ingredient is not an insecticide, but rather an agent to keep larvae from reaching adulthood.
The 2.12 percent cyramazine in Pfizer's Solitude IGR is not an organophosphate. The cyramazine interferes with a fly's production of chitin, a compound that makes up an insect's exoskeleton, or hard outer shell. Flies lay their eggs in manure, but because of this product, the larvae is unable to produce chitin. That means it can't properly form a protective outer shell as it grows, so the immature fly dies without ever reaching adulthood. Rather than being outright toxic to the fly, this product breaks its life cycle.
"Solitude IGR has been proven to help significantly reduce the number of flies that plague horses without creating toxicity issues for humans, horses, other animals, plants, or water supplies," said Pfizer's senior veterinarian, Jay Donecker, VMD.
Farnam's Equitrol II uses Dimilin as its main ingredient, and it works the same way. To administer Solitude IGR (formerly Serene Feed-Through Fly Control), mix a half-ounce in a horse's daily feed ration. It costs $32 for 2 pounds (64 doses); or 6 pounds for $87; 20 pounds for $250. Equitrol II contains 0.24 percent diflubenzuron (Dimilin). Four pounds of it will cost you $17.50; 20 pounds runs $66.
