cows in field

Fly Control on Organic Dairies

Added February 3, 2011. Fly control is one of the top issues facing organic dairy farmers. Summer brings warmer weather, longer days, pasture growth and grazing – things that we all look forward to during the long, cold and dark time of winter. The explosion of life in spring also
brings with it the perennial and unwelcome problem of flies. Flies cause both irritation and serious economic losses to dairy farmers by spreading disease, feeding on animals (causing blood loss) and greatly decreasing productivity in grazing cattle by triggering them to crowd together and stop feeding. Pinkeye, mastitis and other diseases such as bovine leukosis are spread between cattle by the actions of flies feeding on them. Economic losses are difficult to quantify but USDA has estimated that flies often cause a 5 to 20% loss of production for dairy cows. A 10% decrease in milk production (assuming 50# milk/day average) represents about $1.50 per cow daily ($45/cow/month) for an organic dairy. Animal welfare is also an area of concern for all of animal agriculture; a lack of good fly control has the potential to cause serious image problems regarding animal welfare on organic dairy farms.

When one visits organic dairies during the summer it soon becomes apparent that some herds have a much greater problem dealing with fly control than others. The differences are often striking even for farms within a region sharing the same climate and physical features. Organic dairies with good fly control practice a "multi-systems" approach to managing this problem. The managers on these farms work to reduce fly breeding areas, employ multiple tools and strategies to physically trap or deter flies and they also support or augment biological systems that keep fly populations in check. Natural pesticides and repellents that are approved for organic production are sometimes used but the emphasis is on a holistic approach that promotes balance in the farm ecosystem and does not allow fly populations to expand disproportionately.


The number one priority of a fly control program is good sanitation. Many flies such as house and stable flies breed in moist, decaying organic matter. Manure, wet hay, spilled silage, and
soaked grain are examples of things that should be cleaned up regularly. Weekly removal of these materials during the summer months will limit fly reproduction as most flies need from 7-21 days to complete their life cycle. Wet weather can make the cleanup of organic material difficult – covering feed (hay bales, etc.) stored outside and keeping it in a well drained area are important. Organic bedding in the form of straw or hay will support fly breeding when it becomes wet and soiled with animal waste. Prompt removal of dirty bedding and the addition
of lime, gypsum or diatomaceous earth to bedding will limit fly numbers. Some farmers have moved to using washed sand as the sole bedding material for calf hutches during the summer and the result has been lower fly pressure on young calves. Turning compost piles will kill
fly larvae that are in the outside areas of the pile by exposing them to the heating action in the middle. Remember, it's much easier to prevent a buildup of flies through good hygiene than to try and control a fly population once it gets out of hand.

Mechanical Controls

Sticky traps such as fly tapes, ribbons and strings as well as sheets of sticky paper can be used to catch flies inside barns. A large wide tape called the Spider Web™ (~ 1' x 24') is colored and has a scent added to it to attract flies – it can catch thousands of flies before needing to be replaced. Sticky traps should be placed in high areas out of the wind where flies tend to land and rest. Sticky strings sometimes catch birds or bats accidentally – they should not be used in barns with nesting barn swallows.

Fly traps come in a variety of types and sizes. Many are based on the design of jar traps – containers that include bait and allow flies to enter through a one way opening. Organic dairy farmer Kevin Jahnke (from WI) has devised a homemade trap that uses a 55 gallon barrel
and PVC pipe for materials. (See description and figures by clicking here.). For the large biting flies (horse and deer flies) there are specialized traps like the Epps and Horse Pal ® traps. The Alsynite trap consists of a cylinder of clear fiberglass with clear sticky tape on the outside surface.

Walk-through traps have been in use on cattle farms since the early 1900s. The University of Missouri trap contains a double layered screen design that traps flies between screens when flies leave the cows as the cattle pass through the trap. Adding a water spray jet (both above and from the sides below) increases the trap's effectiveness greatly. This design works well for horn flies – a serious pest that feeds on cows by sucking blood many times a day. Horn flies
become active in hot weather and are a tough problem to deal with. Last summer's hot weather extended the time and geographic range of horn fly problems – we saw them farther North for a longer time than has been typical in the past.

North Carolina State University has devised a walk-through fly trap that includes a vacuum that sucks flies off of the cows. This trap has been shown to be very effective against horn flies in the South where horn fly pressure is extreme.

Biological Controls

Parasitic wasps (aka fly predators or parasitoids) are available for purchase in the form of pupae. Immature wasps are periodically placed in fly breeding areas throughout the summer. The tiny wasps lay their eggs on fly pupae after killing them. The newly hatched wasp larvae then consume the rest of the fly pupae. Since flies multiply faster than the wasps the parasitoids must be released at least weekly during the fly season. Research has shown that weekly release of 200 parasitoids per cow
(or 1,000 per calf) can be effective for control of house and stable flies. Fly predators work better in and around buildings than out on open pastures. All farms are different and the results with parasitoids vary depending on factors such as farm cleanliness, weather, neighbor fly populations, etc.

A healthy and vibrant ecosystem with diverse plant and animal species contains checks and balances that limit any one species or group from becoming dominant. Insects such as the yellow dung fly, predaceous beetles and dung beetles are natural predators or competition for fly eggs and larvae. Predaceous mites also consume fly offspring.

Birds are excellent for helping to control fly populations. Swallows and purple martins are very active predators of flies. Encourage these species by placing and maintaining nesting boxes for their use. Poultry are also helpful. Chickens disturb manure pats and consume fly larvae. Ducks (especially Muscovy) consume adult flies and larvae as they forage around the farm.

Natural Repellents and insecticides

These should only be used as supplements to a comprehensive fly control program. The most popular commercially available products include; Ecto-Phyte (Agri-Dynamics) and No-fly (Crystal Creek) based on essential oils; anise, cedar, cinnamon, citronella, clove, eugenol, geranium, geraniol, lemon grass, rosemary, etc. or PyGanic – based on natural pyrethrins. Recently the company US – Agritech has introduced a line of botanical (not essential oil) products (FlyAway, DBX, MiteGard ) for organic fly and pest control – they are available through AgriEnergy dealers.

This article is only a brief overview of fly biology and control. For an in-depth discussion of integrated pest management (IPM) on organic dairies please refer to the comprehensive Cornell IPM guide for organic dairies. It contains detailed information on fly biology and control techniques and strategies.

Further reading

  1. Cornell IPM guide for organic dairies, websites
  2. Walk-Through Trap to Control Horn Flies on Cattle
  3. Purple Martin Conservation Association
  4. The Purple Martin Society

Guy Jodarski, DVM is based in Neillsville, WI and serves as a staff Veterinarian for CROPP Cooperative/Organic Valley. He works in an organic and sustainable livestock practice with an emphasis in dairy cattle herd health. Dr. Jodarski has been in practice for 23 years and enjoys teaching how to keep food animals healthy without the use of antibiotics, synthetic hormones and chemicals.