If you have more rain than normal you will likely see more flies. Since pest fly eggs and larvae need to be in a moist medium, if it’s wetter than normal more breeding areas will stay just perfect longer for producing lots of flies.
Flies have a staggering reproduction potential with each female fly laying up to 900 eggs. Thankfully due to natural predation (from beneficials like Fly Predators, beetles, mites, ants, birds, etc.) plus the need for a moist environment for development, only 2-4% of fly eggs generally make it to adults.
But a small favorable change to factors affecting their survival rate, like more rain (or decimating the beneficials with pesticides) can mean a huge increase in the numbers of flies. This is one of the reasons why there are “good” and “bad” fly years. Also, it only takes one burst of wet weather, in an otherwise dry year, to yield a larger than normal hatch of flies which then can hang around for nearly a month.
If do you have a rainy spell, by reacting quickly and stopping the extra reproduction before the fly population builds up, it will take less effort and cost than waiting until the flies are intolerable.
Surprising as it may seem, flies need a place to rest and get out of the heat or cool temperature. Weeds and tall grasses are perfect for this so if you remove weeds from around buildings you can “encourage” pest flies to hang out elsewhere.
The “perfect storm” location for optimum fly production on many dairies are the calf hutches or pens. In these you have the most productive manure of any bovine (from the calf’s diet), ongoing moisture from the urine, rotting vegetative matter (if you bed with straw) and that whole goopy mess stays that way for 45-60 days, enough for six or more generations of flies.
This super abundance of flies can not only slow calf growth and spread disease but if you combine this with poor ventilation, the ammonia produced from urine can permanently impair your calf’s respiratory system.
The best solution would be to clean these areas at least weekly, but if that is not possible at least change the bedding during warm months.
Studies in the 1980’s showed that within the first six weeks of occupancy, individual calf hutches bedded with straw in the summer produced many more flies than hutches bedded with shavings, sawdust or sand.
A more recent study of different bedding materials in heifer growing pens showed that over 12 weeks of occupancy, straw bedding packs produced many more adult Stable and House Flies than packs formed with shavings or sawdust.
While our Fly Predators will help counteract the excess fly productivity of straw, you will need to use many more of them than if you simply changed bedding in the summer.
Dr. Bill ClymerFort Dodge Animal Health, Dr. Roy EllisPrairie Pest Management, Dr. Kevin FloateAgriculture and Agri-Food Canada, Dr. Robert M. Miller, DVM, Dr. William QuarlesBio-Integral Resource Center. All illustrations 2006 Dr. Roy Ellis.
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