Battling Flies

 By Heather Smith Thomas

 Flies are a continual problem during warm weather, but there are several ways to reduce these pests.  Different flies have different habits and behavior, so a combination of tactics is most effective if you are trying to control several types of flies.  Stable flies breed in rotting organic matter such as old hay, silage and bedding.  Horn flies breed in fresh cattle manure but spend all their adult life on cattle.  Horseflies/deerflies breed in wet areas, often many miles away—impossible to control them at their breeding sites.

Sanitation And Physical Removal Of Breeding Sites
Stable flies can be controlled effectively by cleaning up old organic debris, like wasted hay around bale feeders.  About 95% of the stable flies develop in less than 5% of the area where cattle are located.  If you can clean up those areas and rotting material before fly season starts, spreading the piles so they can dry out, or composting them, this debris won’t propagate flies.  If you put black plastic over compost piles you can bake the maggots.

Biologic Strategies     
These tactics include use of other insects or animals to feed on fly eggs, larvae or adults.
Parasitic wasps - These tiny wasps lay their eggs in fly pupae in manure and debris, and the developing wasp eats the fly pupae before they hatch into flies.  The key is to start using them early in the season before the fly population grows large, sprinkling them around the barnyard and adding additional wasps every 4 weeks.  These can help control manure-breeding flies in a small area like a barnyard or dairy but won’t work in a big pasture.
Dung beetles – These beetles reduce horn fly numbers dramatically by disrupting the manure pat.  These insects spend their lives in manure.  Adults use liquid components as nourishment and lay eggs in the manure pat.  Hatching larvae consume manure.  Some species remove and bury balls of manure containing their eggs.  An active population of dung beetles can bury or destroy 95% of horn fly eggs and larvae and about 90% of other cattle parasites that are passed in or depend on manure.  Even if fly eggs hatch, they can’t get back up to ground surface after dung beetles bury the manure.  Birds are attracted to manure containing dung beetles, and tear the pats apart to eat them—which helps spread manure and disrupt fly larvae development.  A single manure pat without dung beetles can generate 60 to 80 adult horn flies.
Chickens or ducks - Some stockmen with small herds augment fly control with free-range chickens or ducks.  In conjunction with intensive rotational grazing, they follow the cattle, scratch through manure pats to eat the “bugs” and destroy these breeding sites for horn flies.  Muscovy ducks eat insects and don’t need commercial feed.  The ducks follow cattle around, searching through manure and scattering the piles--and no fly larvae survive.  It takes about 4 ducks per cow to adequately control the fly population. The ducks also eat adult flies and pick flies off cattle when they are lying down chewing their cuds.  

Fly Traps
There are several kinds of fly traps and some work best for different types of flies.  Some are effective for horse flies and deer flies, and there are also traps for stable flies (sticky traps they land on).  The only trap that removes horn flies is a cow vacuum, in an enclosed area the cows walk through; it blows the flies off the animals and sucks them into a bag.  It’s expensive and used mainly in dairies--set up somewhere  the animals have to go through it.  It also utilizes.
    
Chemical Control With Pesticides
There are many kinds of sprays, pour-ons, injectables, etc. for killing flies.  
Dust bags and oilers - Back rubbers, oilers and dust bags are helpful in situations where cattle must go through a gate, or learn how to use them in a small area.  Cattle enjoy rubbing on these because it gives some relief from horn flies.  The dusts and liquid products (for oilers/rubbers) work well, as long as flies have not developed resistance to these chemicals, and you keep the applicators filled.
Pour-on products – There are numerous types of pour-ons containing various chemicals including pyrethroids, permethrins, and the avermectins that target both internal and external parasites.  Some of these are affective against horn flies for several weeks.
Insecticide ear tags – These are probably the most popular control method for beef cattle and non-lactating dairy cattle because the tags can be installed in early summer and possibly control horn flies and face flies through most of the fly season.  There are numerous brands, containing pyrethroid, organophospate, and avermectin insecticides. Depending on the product, one or two tags are installed per animal.  Horn flies in some regions and on some farms have developed resistance to these chemicals, however.  
Feed-through products – There are several kinds of feed-through products that are added to feed or mineral mixes.  They end up in manure and affect the flies that lay eggs in fresh manure.  Some of these products contain a larvicide that kills the fly larvae, while other products contain insect growth regulators which affect the larvae, and they don’t mature to become flies.
Injectable parasiticides – These products contain macrocyclic lactones that mainly target internal parasites but can also kill external parasites that feed on blood (such as horn flies).  
Space sprays – These are concentrated products you add to several gallons of water, for spraying around a barnyard or in a barn.  It provides quick knockdown and long-lasting control of most biting flies and mosquitoes.

Resistant Flies
Nancy Hinkle, PhD, Professor of Veterinary Entomology, University of Georgia says the cattle industry unfortunately has become dependent on insecticides and is faced with generations of flies that are resistant to these weapons. “We need new methodology for cattle, especially to control horn flies.  Any chemical control program for horn flies must alternate/rotate different chemical classes as the flies become resistant to whatever is being used,” she says.

Breeding Resistant Cattle
A few people are developing lines of beef cattle that are less attractive to horn flies; some breeds and some individuals within breeds are resistant to these flies.  With selective breeding a person can utilize genetically resistant animals and select for that trait.  “It is doable, but something a person must commit to.  Today, with more knowledge of genetics, we can probably cut down the time it would actually take to produce fly-resistant cattle,” says Hinkle.