STRATEGIC FLY CONTROL IN SHEEP

Why timing of treatment is important

The seasonal nature of fly activity provides unique opportunities for strategic control that can significantly reduce fly pressure and reduce the risk of blowfly strike. Treating sheep early in the season with an effective and long-lasting chemical prevents fly numbers from building up by removing the host environment required for the flies to reproduce. Conversely, treating sheep late in the season reduces the number of flies that can contribute to the fly population in the following season. 

Australian sheep blowfly, Lucilia cuprina lifecycle

The Australian sheep blowfly, Lucilia cuprina, is the primary fly species responsible for initiating flystrike in sheep in Australia. This species is largely dependent on sheep as a breeding resource¹, with female flies laying eggs in moist wool subsequent to a protein meal and mating. After hatching, fly larvae then moult through three larval stages (i.e. maggots) and eventually leave the sheep to pupate in the soil.  

The entire life cycle can be completed in 2.5–3 weeks² – with variation depending on exact environmental and soil temperatures.  Fly numbers can therefore build up very rapidly under suitable environmental conditions, assuming susceptible sheep are available as a breeding resource. In cooler conditions at the end of the fly season, development is inhibited or ‘arrested’ at the prepupae stage and development is not resumed until conditions are again suitable.

The increase in soil temperature in spring in south-eastern Australia has been shown to trigger the synchronous emergence of the first generation of flies for the new season,³ regardless of when the larvae were deposited.  

Lucilia cuprina therefore has the ability to adapt to the environment and changing seasonal conditions.  Flies will keep developing well into the “colder” months if temperatures remain relatively mild – and the re-emergence of flies at the start of the fly season will vary depending on the actual temperatures experienced.⁴

Advantages of early season application

If chemical treatment is applied to sheep before flies emerge at the start of the fly season, sheep are essentially removed as a resource for the propagation of the fly population when the first generation appear. As emergence is relatively synchronous and the first generation is typically small, this can have a significant effect in reducing fly numbers and the risk of flystrike for the rest of the fly season. 

This strategy has been demonstrated to work very effectively on commercial sheep farms in different regions and over a number of years with varying seasonal conditions⁵. 

 Flies are not capable of moving long distances, so the success of early season treatment can be even further enhanced if all sheep on a farm are treated, if neighbours treat as well and/or if flocks are physically isolated.⁵ 

If chemical treatment is applied (or still active) on sheep in late summer and autumn, sheep are again removed as a breeding resource for the fly population. At this time, this has the effect of reducing the number of larvae that enter arrested development and therefore the size of the first generation of flies that will emerge the following fly season.³ 

Farm management practices

Optimum fly control will also depend on farm management practices. Integrating early or late season treatment with shearing and crutching of sheep during spring, early summer and autumn will further reduce susceptibility to flystrike and contribute to reducing fly numbers.⁵ 

 Depending on the length of the fly season and the product used, a single treatment may provide both early and late season strategic fly control. In areas with a longer fly season, one or the other may be preferable depending on time of shearing – remembering to be conscious of wool withholding periods. In years with a late or delayed start to the fly season due to seasonal conditions, late season treatment is even more crucial. 

CLiK™ Extra

Australian sheep and wool producers have relied on CLiK™ Spray-On to provide season-long protection (18–24 weeks) against blowfly strike for over 20 years. CLiK Extra sets an even higher benchmark by protecting sheep from flystrike for up to 29 weeks in a single application.  

CLiK Extra contains 30% more dicyclanil than CLiK Spray On.  Dicyclanil is the same proven active ingredient in CLiK Spray-On.⁶ Dicyclanil is a potent insect growth regulator that interrupts the lifecycle of blowflies.⁷ It prevents emerging larvae from moulting into damaging second stage maggots, thereby preventing flystrike.  

CLiK Extra protects against blowfly strike for up to 29 weeks, as well as protecting mulesing and marking wounds against flystrike.⁶ CLiK Extra is ideal for strategic application early in the season. Australian research confirms that early season treatment can reduce the build-up of the blowfly population and reduce the risk of blowfly strike later in the season.^1,5 

CLiK Extra’s two-band application technique for sheep >30 kg liveweight improves coverage and protection against breech strike, the most common site of blowfly strike in typical years.^8,9 

CLiK Extra will help reduce selection pressure for resistance where it remains above the minimum effective concentration (MEC) throughout the entire season and until flies are no longer active. This will also reduce the need for repeat treatments within the same fly season.¹⁰ 

CLiK Extra gives you extra peace of mind that your sheep have the longest protection available against flystrike, particularly with unpredictable fly seasons. Always read and follow label directions.