Sound familiar? If this is our reaction, can you imagine how your horse feels – even worse if the flies are of the biting variety! I'm going to talk about the impact that flies have on any yard – regardless of the number of horses. I will place emphasis on not only addressing the problem of the adult flies, but also the immature stages, which is the source of all of the problems.

At the outset I'd also like to appeal to you, the horse owner, to do the same, if you are serious about getting to the base of your fly problem, because integrated fly control is not a once-off exercise that is tackled half-heartedly.
The word "integrated" in "integrated fly control", refers to using various methods and tactics to address each stage of the fly's life-cycle with the intention of reducing overall fly numbers. A question that I often pose is: "What would you say if the local police only arrested drug users and not the drug dealers?" In the case of a fly problem – you must reduce the fly breeding areas, and you must target control measures at the immature stages of flies!
The most common flies associated with horses and stables, are the house fly (Musca domestica), the stable fly (Stomoxys calcitrans), which is a biting fly, and the horse fly (the Tabanids), which is also a biting fly and occurs in areas where there are other large grazing wild mammals (antelope and zebra).

Here are some good reasons to protect horses from flies:
• The painful bite of a stable or a horse fly, may cause the horse to jump or react in a way that may be dangerous for a mounted rider. The impact of fly-worry has been demonstrated in many field trials, not lab trials, that the pure physical irritation of flies causes livestock (cattle) to lose between 25 min and 4,5 hours of eating time per day! If this is the effect on cattle, that have thicker skins and don't sweat, can you imagine the effect on a horse?
• The physical pain or irritation of a bite would fall under the above reason, but often insect bites stimulate an intense secondary allergic skin reaction which causes the horse to itch and scratch long after the pain of the actual bite has gone.
• Flies, especially biting flies, also have the potential to transmit various diseases – although midges are probably more guilty because of their role in transmitting African Horsesickness (AHS). Often the measures taken to control flies (such as fly fringes/nets; daily application of a pyrethroid or repellent), also help to limit the impact that midges may have.
• Very importantly, flies serve as an intermediate host or actual transmitter of certain worms and their immature stages (such as bots, Habronema spp, etc).
• Not forgetting of course the secondary infestation of a wound with blow-fly maggots and screw worm!

Essentially there are three ways to control flies in an integrated way.

Cultural methods
Essentially this refers to reducing the breeding areas of flies as well as factors or situations that would attract flies. Flies are attracted to warmth, moisture and organic matter, where they can feed and lay their eggs. Common sense should tell you that areas where feed has been spilt, manure heaps (even if manure is in bags), compost heaps and stable bedding are ideal places for eggs to hatch into maggots!

If you aren't sure, scratch around until you find the area where there are maggots and pupae. It is worth knowing that a horse, depending on its diet of course, can "produce" up to 16 kg of manure a day, and only 1 kg of manure is all that is needed to sustain the survival of 5 000 larvae (maggots) which will then develop into pupae and then into adult flies.

Biological methods
This involves the use of natural predators of flies and their immature stages. There are certain mites and beetles that love feeding on fly eggs and larvae. There are also a number of wasp species who lay their eggs in the fly pupae, which leads to the death of that pupae.

Even though I want to stress the uses of certain chemicals to control flies, I would be lying if I said that encouraging biological control was not a good idea. It is a very good idea to introduce batches of these wasps 2-3 times a year.
The only downfall is that the effect, and results, are occasionally inconsistent – through no fault of the company that sold you the wasps or the wasps themselves. It is a simple case of the fact that you are dealing with biology, and there will never be enough wasps, beetles or mites to cope with the sheer volume of flies, especially on a property housing many horses, for the whole year or season.

If I was an intensive farmer (dairy, feedlot, pig or poultry) or horse stable owner, there is absolutely no doubt in my mind that I would make use of parasitic wasps and encourage certain beetles types. Unfortunately, there aren't many properties with an issue with flies, that can get away with not using chemicals at all.

Chemical methods
If applied correctly, chemicals are arguably the most effective method of reducing fly numbers. I'm not talking about enviro-unfriendly organophosphates or DDT – I'm talking about using modern, safe and effective chemicals. These can be broken up into adulticides and larvicides – the former kills the adult fly, and the latter affects the larvae.
Probably the most commonly used adulticides are the members of the pyrethroid group, such as cypermethrin and deltamethrin. These provide a very effective knock-down effect for application on the animals themselves, as well as walls and ceilings.

Depending on the fly load and the risk (near low-lying areas or in AHS risk areas), they would probably need to be applied every week, but I would strongly suggest that, especially in summer, you apply (sponging or spraying) these pyrethroids daily or even twice daily. Remember, pyrethroids (all members of this group) are deactivated and broken down by sunlight, especially direct sunlight, thus my reasoning behind recommending daily application.
Another adulticide, completely unrelated chemically to the above-mentioned chemical groups, is thiamethoxam (e.g. Agita fly bait). Agita kills flies when they ingest some of the bait, and also kills them when they come into contact with the bait. It is formulated with pheromones and a sugary substance, thus attracting the flies. These fly baits can be sprinkled strategically as a dry bait or painted on. And because of its formulation, not only can it be very effective, but a very little also goes a long way! Bear this in mind when you get to the till!
But because your mindset has changed and your approach has become an integrated one, you will soon see (within 2-4 weeks) that once you use a safe and effective larvicide as well, adult numbers will drop and the amount of adulticides needed will lessen.

A larvicide such as cyromazine (e.g. Neporex) is formulated as granules that can be sprinkled, or as a powder that is mixed with water and then sprayed wherever the larvae occur. Have a scratch around for breeding sites or any other organic, warm and moist area. Apply the cyromazine to these areas. It will prevent larvae from progressing to the next stage (pupae) by preventing chitin synthesis. In this way you are eliminating about two thirds of the problem.

Depending on the fly numbers and the season, cyromazine should be applied every two weeks until the numbers have reduced dramatically. Speaking of which, it works best to use a larvicide before you notice many adults, i.e. before the "season" (in September) although it's never too late to make an impact. This will reduce the number of viable pupae before they moult to become egg-laying adults.
The other important advantage of cyromazine is that it has minimal effect on the natural predators, e.g. the wasps that we spoke about or the birds that feed on the maggots. Cyromazine also has no negative effect on fish. Another aspect to bear in mind is that some of other larvicides on the market kill the fly larvae indeed, but they kill the "friendly" insects as well!

You will notice a difference in the adult fly numbers within a few weeks of using larvicides such as cyromazine – and as long as an integrated approach is used, i.e. reduce breeding areas, make use of biological methods as well, and the use of effective adulticides and larvicides, the only thing that could throw a spanner in the works, is if all of your neighbours are not as progressive as you are.

For more information, contact Dr Barry Coates on 082 901 5810.