Our Organisation Search
Quick Links
Toggle: Topics

Put a plan in place to deal with blowfly strike

Put a plan in place to deal with blowfly strike

As we head into June, we are entering a high risk period for blowfly strike with a number of cases appearing on farms, writes Teagasc Sheep Specialist, Ciaran Lynch.

For blowfly, the season starts as early as April as temperatures increase and continues right through to October. It can also occur outside of this window where conditions allow. The level of burden experienced within a flock is influenced by both the prevailing weather and on-farm conditions. It can pose a significant challenge when correct prevention measures are not in place

Strike will typically occur on soiled areas of the fleece first, as the flies are attracted to these areas. This is typically around the tail end, but strike can also occur on the back, shoulders and undercarriage as well as in the feet or anywhere there is any open wound, such as the head. During the initial phase of strike, the animal may be away from the main group and appear agitated often biting or kicking at the affected area.

Blowflies are attracted to organic matter or discharge. Soiled, dirty fleeces from animals with scour, footrot or open wounds that may occur from shearing or rams fighting increase the risk. They are also highly attracted to sheep where strike has already occurred. In damp, humid conditions, this risk is heightened.

  • Have an effective internal parasite programme in place on your farm;
  • Dag/crutch/shear dirty sheep;
  • Treat any incidence of strike promptly.

Treatment options

The aim should always be to prevent blowfly strike from happening in the first place. There are a number of different options that are available to farmers in this regard.

Plunge dipping

The efficacy of this method is dependent on correct dipping procedure, ensuring the dip is made up to the correct strength and replenished periodically following manufacturer’s instructions at specified intervals. Sheep should remain in the solution for a minimum of 60 seconds. The duration of immersion in the dip solution is strongly correlated to the length of time that protection will last for.

Topical applications

This is the most common method used on farm. There are a number of products available offering periods of cover from 7 to 19 weeks.  Correct application method will have an impact on the efficacy. Ensure the gun used is calibrated and delivering the recommended amount, and that it is applied evenly in the designated areas as per manufacturer’s recommendations. Applying to soiled or contaminated areas will greatly reduce product efficacy. The meat withdrawal dates vary from 7 to 40 days for these products, so care needs to be taken to ensure they are suitable for the farming system.  Given the fact that blowfly season is quite long, a repeat application may be required in many cases once the period of cover nears its specified duration.

These common products used can be split into two categories based on their active ingredient and mode of action:

Insecticidal pour-ons

There are a number of pyrethroid based pour-ons (e.g. cypermetrin – Ectofly, Vector etc.) which offer short-term cover (6-8 weeks) from flystrike on the areas where they are applied. These products will also kill maggots if they are applied directly to the larvae.

Insect Growth Regulators (IGRs)

Dicyclanil-based products (e.g. Cliczin, Clik, Clik extra) work by interrupting the life cycle of the larvae. They prevent the stage one larvae, that don’t cause harm, from developing into stage two larvae that have mouthpieces and can cause damage. These products won’t kill stage 2 or 3 larvae (maggots) and therefore must be applied before the blowfly lays eggs. There are a number of different products within this category on the market with varying lengths of cover from 8 weeks up to 19 weeks.


The fleece provides an ideal incubation ground for the fly to lay her eggs and shearing will remove this. However, this protection is only short lived and strike can occur within weeks during high risk periods and, as a result, one of the outlined methods above will need to be incorporated into the control programme for these animals.

Key points to remember for treatment:

  • Have the control method in place before strike occurs;
  • Use products correctly in accordance with manufacturer’s instructions;
  • Be aware of the periods of cover provided by each product and the withdrawal dates when selecting stock for sale.

Put a plan in place to deal with blowfly strike this season, contact your advisor or veterinary surgeon to discuss this further.

In the below video, Michael Gottstein, Head of Sheep Knowledge Transfer Programme at Teagasc, offers key advice on the prevention and control of blowfly strike: