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Moos News

Managing Fly Populations in Dairy Barns

Managing fly populations in dairy operations is a constant concern for most producers. High fly populations can cause stress for the animals, and negatively affect dry matter intake and milk production. Flies can also act as disease vectors and can carry pathogens including mastitis causing bacteria. It is therefore important to have a comprehensive approach that uses all available techniques to manage flies. The barns offer flies perfect conditions such as heat, moisture, and plenty of organics (feed and manure).


All flies pass through 4 life stages: egg, larva (maggot), pupa, and adult. Females will deposit eggs on moist manure or any type of moist rotting or decaying organic matter. The eggs hatch in 10-12 hours and the maggots move into the wet organic matter. Fly maggots mature in 4-5 days under warm moist conditions. Pupation occurs in the drier parts of the manure or bedding with the adult flies emerging in 3-5 days. Under ideal conditions, a house fly can complete its life cycle in 9-14 days. It can also be much longer in cooler temperatures.


When spring begins, flies become more active. An early start in spring for fly control is the best strategy. One house fly can lay 2000 eggs in an average 6-8 week lifespan so populations will grow exponentially as the season progresses. A single fly in April, may produce up to 64 million flies by the end of July or August under ideal conditions. In the barn, visible adult flies represent only 15% of the population. Eggs, larvae, and pupae that are hidden in the manure and bedding account for another 85%.


Fly Control Strategies


Building Treatments:


• Fogging

To eliminate adult flies, fog the barn with a fast acting pyrethrin based insecticide (Disvap IV) when the barn is empty. Leave for 2 hours and ventilate before re-entry. Pyrethrin kills insects rapidly but does not have a lasting effect. It is also possible to use spray cans (Disvap Spray or Multivap Spray) for spot treatments such as around windows, lights and the milk house. Make sure to use an approved insecticide for the application intended and follow the directions for use.


• Residual Insecticides

For a long acting effect, apply a residual insecticide (Disvap V or Zap-IT Insecticide) to walls, posts, window ledges and ceilings. This application will have residual activity for several weeks. One can also do external applications and should be repeated at least once per month due to sun and rain breakdown of the insecticide.


• Granular Baits

Use granular bait in low ventilation areas. Bait contains pheromones to attract the flies to feed on them.  In highly ventilated areas, the attractiveness of the bait is diminished. For regulatory reasons, only use baits in bait stations. Spread out the fly bait stations within the barn. One station will cover 1000 cubic feet of air space. They should be placed at the beginning of fly season and renewed once weekly during warm weather



Livestock Treatments:

It is always important to read and follow the label before using any pesticide. Be sure to read the claims for fly control on livestock insecticide product labels- some fly species may not be well controlled by some products. Resistance can also occur which may necessitate rotating products if losing efficacy.

• Non-Systemic Pour Ons:

Vetolice, Lice-Away – are non-systemic pour ons (1%  permethrin) to control biting lice and horn flies on both lactating and non-lactating dairy cattle. Apply by pouring along the back and may also be applied to the face with a cloth (avoiding the eyes, nose and mouth). Apply 15ml per 100lbs up to a maximum of 150 ml per animal. They have residual activity and treatment can be repeated as needed but no more than once every two weeks


Boss Pour On – is similar to above but is 5% permethrin so dose is only 3 ml per 100lbs with a maximum dose of 30 ml per animal.


Cylence Pour On – is a different active ingredient (1%  cyfluthrin) applied 2 ml per 100-200lbs to a maximum dose of 12 ml per animal and only every 3 weeks to a maximum of 3 applications per year.

Saber Pour On – another different active ingredient (1%  lambda-cyhalothrin) approved for non-lactating cattle only and applied at a rate of 10 ml per for less that 600lbs, and 15 ml if greater than 600 lbs.


Zap-It Insecticide – is an aerosol spray which can be used on both lactating and non-lactating dairy cattle. It kills face flies, stable flies, horn flies, and house flies. Spray about 3 seconds on each side being careful to spray the back, withers, and forelegs thoroughly. Avoid spraying the udder and do not spray into the eyes. Zap-It has residual activity and treatment can be repeated as needed.


Disvap IV – is an oil based spray which can be used on dairy cattle to control flies, including horn flies, stable flies, and house flies. It is a quick knock down insecticide without residual activity. Apply 30-60 ml per animal using a sprayer which produces a fine mist. Cover the entire animal lightly without making the hair wet, and avoiding the udder, eyes and mouth. Repeat once or twice daily as required and treat cattle at least 20 min before milking, and wash the udder before milking. 


Control and Monitoring


For continuous protection with animals present, use sticky sheets, rollers or strings (Silvalure) attached to posts, walls, ceilings and milk pipes. They are most effective in high fly traffic areas. Installing them around lights will enhance the effect of these traps as flies are attracted to lights. Use often and early in the season to reduce reproduction.  Fly zappers or electrocutors can also be used in low risk areas for fire such as milk houses. 


Eliminating Flies At The Source


Since flies reproduce in damp areas, manure and bedding management is one of the key elements for fly control. Calf pens or hutches are very common fly breeding areas inside and outside. In the summer with high heat and humidity, their life cycle can be as short as 7- 10 days. Thoroughly scrape stalls and pens weekly to reduce reproduction. Pay attention to corners and edges where manure can accumulate.


At the end of the fly season in the fall, the barn should be washed using an alkaline detergent (Biosolve Plus) to remove stains left by flies. These stains contain bacteria which can cause disease and pheromones that can attract other flies to the barn. Flies can smell up to 750 yards away. A barn full of stains is a magnet for flies.


Increasing ventilation will help drying of reproductive sites. Portable fans can be installed in areas where flies gather. It will also protect the cows from flies when the cows are resting.



Fly control is best accomplished using a multi-pronged approach. Simple spraying for flies will have some immediate and visible effect, however fly control to reduce populations for the long term involves a combination of waste management, barn hygiene and effective insecticide products.

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