Fly Management in Organic Dairy Production

Fly management can be a serious issue for organic dairy producers, as chemical-based insecticides are not permitted for control of pest flies. Flies not only carry diseases, but can also distract and annoy cattle while they are grazing or inside barns. That means less milk production, less weight gain and an economic loss for farmers.

In pastures, the horn fly, which feeds on the blood of animals and is observed mainly on the backs, and the face fly, which can cause diseases such as pink eye, are the most problematic. Inside buildings, it is the house fly and the biting stable fly that cause the most difficulties.

Fly management must be undertaken using various methods simultaneously. The adult stage is when the fly becomes a pest for the livestock and therefore the goal should be to limit the adult population in barns or in pastures. This is best accomplished by targeting the fly before it reaches adulthood (control of the eggs, the maggots and/or the pupae). The most efficient method is the removal or cleaning of manure and other organic residues where adult flies lay their eggs and where maggots grow. A substrate rich in organic matter and containing about 70% water is ideal for fly breeding. Keeping the bedding dry and removing the bedding from pens at least once every 10-12 days should decrease the number of adult flies emerging. We usually find fewer flies in barns with tunnel ventilation, as the bedding and manure dry up quickly the bedding quality for egg-laying and maggot development decreases. Moreover, the adult fly does not like a windy environment.

The type of bedding may also have an effect on the number of flies. Straw bedding seems to result in a higher number of flies compared to woodchips. Adding lime or diatomaceous earth to the bedding is another practice that seems to help, by decreasing the suitability of the bedding for egg-laying or maggot development.

A large array of sticky traps are available for use in livestock production. Each of them may be well designed for a particular purpose. However, it has been noted that the "clothes line" type of trap is usually the most efficient at capturing flies inside the barn (for example Sticky Roll™, but this type of trap is also sold under other brand names). This system is also easy to install and the rolls are easy to change.

A few trap types are designed to attract and catch adult flies outdoors by using bait. Their efficacy will depend upon the type of bait used and often the species of flies captured may not be the target ones. This type of trap might help slightly, but other methods are more efficient.

A few organic producers are using a mixture of essential oils applied directly to the animals to repel the flies. The efficacy of some essential oils to repel insects has been studied and tests are currently being performed to evaluate repellent properties against the most common pest flies in livestock production. The use of plant extracts shows great potential. However, before using a product to control or repel a pest insect, it must be registered by Health Canada's Pest Management Regulatory Agency (PMRA).

A few commercially available biological control agents, such as, parasitic wasps, nematodes, hister beetles and predatory flies, can be purchased and released in livestock farms. Although they attack the eggs, the maggot or the pupae, ultimately decreasing the number of adult flies in the barn, research has shown highly variable results. Careful selection of the species used, the release rates and the adoption of other management methods are essential. Make sure your provider has expertise in biological control. Parasitic wasps seem to be more effective with horses in stables than with other livestock animals. More research is needed to improve the efficacy of the bio-control agents.

Fly management for organic producers is certainly a challenge and there is no panacea. The first action that should be undertaken is appropriate cleaning and management of organic matter in barns (manure, urine, bedding and feedstuff). Curative methods will prove to be more expensive than preventative measures such as appropriate cleaning.

A research project has been undertaken at the Université de Guelph - Campus d'Alfred to develop reduced risk and biological methods to provide options to organic and conventional dairy producers. Dr. Simon Lachance, from the Centre for Organic Dairy Research at the Université de Guelph - Campus d'Alfred, is leading the project, and participants are organic producers in the area. The parasitic wasps used for this project are reared by IPM Laboratories Inc. in New York State.