Blowfly Strike Control Calendar for Sheep Farms

A seasonal approach to blowfly strike prevention aligned with fly activity patterns provides the most effective protection for sheep welfare.

Key Facts

Lucilia sericata fly activity in the UK peaks between April and October
First strike of the season typically follows warm, humid weather in April or May
Prevention should begin before the first high-risk period, not in response to first cases
Chemical preventives have different durations: 8 weeks (cypermethrin), 16 weeks (dicyclanil), 19-24 weeks (cyromazine)
Monitoring trap catches of green bottle flies predicts risk periods before strikes occur
Dagging (removing soiled wool) in spring reduces strike risk significantly
High-risk individual animals (wrinkly skin, high worm burden) warrant targeted monitoring

Welfare Considerations

A calendar-based prevention program eliminates the reactive approach that allows welfare emergencies to occur before action is taken. Waiting for the first strike of the season to apply preventives means one or more sheep have already suffered. Prevention applied before risk begins - based on seasonal fly activity patterns rather than first cases - eliminates suffering rather than treating it. Combining chemical prevention with management strategies (dagging, wool removal from high-risk areas) provides the most comprehensive welfare protection.

What You Can Do

Apply preventive treatments before the start of the fly season in your region
Use trap monitoring to predict fly activity peaks and time preventive applications accordingly
Dag all ewes in spring to remove soiled wool before fly activity begins
Inspect all sheep daily during the peak risk period (April-October in temperate regions)
Record strike cases to identify high-risk individuals for priority monitoring in future seasons