STRIKE CONTROL

The pattern of strike
Strike risk
The effects of control on strike

THE PATTERN OF STRIKE

The pattern of strike expected in an average year. Variation in this pattern may be caused by differences in weather, patterns parasitic worm burdens or husbandry practices, such as shearing.

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STRIKE RISK

Strike risk is increased by:

warm weather
high humidity (summer rain)
undocked tails (in lowland flocks)
faecal soiling (daggy sheep)
lowland flocks
high blowfly numbers
foot rot
head wounds in rams
thick fleeced breeds
lack of preventitive insecticide use

Strike risk can be reduced by:

good parasitic worm control
tail docking (in lowland flocks)
dagging & crutching
foot rot management
shearing
frequent flock inspection especially at high risk times
appropriate insecticide use

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THE EFFECTS OF CONTROL ON STRIKE

The model can be used to give advance warning of approaching strike problems over the blowfly season and predict the efficacy of various control techniques and husbandry practices.

The model can show the effects of different timing of insecticide treatments. In the figures the model shows the expected impact of applying an insecticide against fly strike under typical husbandry and weather conditions. The insecticide is assumed to be 99% effective when applied and to have a half-life of about 6 weeks and residual activity of about 8 weeks. In figure A, the treatment is applied to both ewes and lambs once, following typical practice, when the blowfly challenge is at its peak at the end of July.

FIGURE A

Treatment is applied to both ewes and lambs once, following typical practice, when the blowfly challenge is at its peak at the end of July

In B, treatment is applied to both ewes and lambs once, in early May, before the blowfly population can increase in abundance.

FIGURE B

In C the insecticide is applied twice, once at the start of May, and once in late July.

FIGURE C

The model clearly shows that the appropriate timing of treatment can have a major impact on the level of flystrike. Treating for strike later in the season, once blowfly numbers have already peaked makes the disease more difficult to control. Early season application, before the blowfly population can increase substantially in numbers, is particularly important. But, with the type of treatment modelled here, two applications are required to maintain a low strike risk throughout the year. The strikewise model is able to pinpoint the correct timing of these applications with accuracy.

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