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South Australia worms, flies and lice update - January 2020

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (

Consecutive dry years across most of the State (in fact the driest 36 months on record across the southern States) combined with widespread, devastating bushfires through December and January has made conditions unpleasant for farmers, animals and worms alike. The further concern is that there is plenty of summer to come and no rainfall in sight. The Indian Ocean Dipole was at the strongest positive since 2001 (when the BoM’s weekly dataset commenced) and typically, the forecast was for “below average winter–spring rainfall to southern and central Australia” plus, it is “often associated with a more severe fire season for southeast Australia”….surprise, surprise!

Recent worm egg counts indicate 20–25% of mobs of ewes or lambs have had sufficient worm burdens to warrant a summer drench. This is atypical of recent summers, but highlights the impact of little or no topsoil moisture in most regions as well as the importance of monitoring before considering drenching. Those mobs with significant worm burdens have had mixed infections often indicative of an extended period since their last drench.

The seasonal outlook is not encouraging, but ongoing monitoring is important, especially in mobs that have not been drenched for several months. The same applies to livestock being confinement fed as they are more likely to access worm larvae under confined stocking conditions if there is any moisture on the ground from rain or leaky watering points. A drench prior to confinement will usually be warranted unless monitoring indicates negligible worm burdens.

Monitoring during summer is also recommended about 3 weeks after significant rainfall i.e. in excess of 20mm (when the evaporation rate is high and soil moisture is low) as this can precipitate Haemonchus (barber’s pole) infections to emerge leading to rapid escalation of potentially fatal worm burdens.

If there is a silver lining to such dry conditions, flystrike tends to be substantially reduced. Urine stain is always a potential nidus for infection, but scouring is rare and body strike from moisture non-existent. In addition, shearing or crutching during spring through to autumn further reduces the risk. On that cheery note here’s hoping the seasonal conditions take an unexpected upturn.

For January 2020 state outlooks, please follow the links below:
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