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South Australia worms, flies and lice update - September 2019

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Recent rainfall has given some hope of a reasonable spring across South Australia, but minimal subsoil moisture means frequent rain will be required to maintain pasture and crop growth into October. Some crops in drier regions have been cut for hay while others showing little potential will be grazed.

Worm egg counts across agricultural areas including the south-east have generally been low with only the occasional ewe mob having counts high enough to warrant drenching. These results highlight the importance and cost-effectiveness of monitoring to determine if drenching is necessary. Even lambs approaching weaning should be monitored to establish if a drench is needed. In addition, monitoring is critical during October/November to decide if a summer drench is required.

These results indicate little prospect for doing drench trials in weaners this spring, but there is still scope to do a worm egg count 10 days after drenching to establish if a drench has been effective. If drenching is indicated, triple-active products should be used to minimise the risk of drench resistance developing. In addition, refugia strategies should be employed to further minimise the risk of resistance i.e. either leave 10–20% of the mob undrenched, or return the mob to the paddock they have been grazing for an additional week before putting into a fresh paddock. This strategy promotes the spread of susceptible worm larvae across the property, and so maintaining a population of worms that may be controlled by drenching if necessary.

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