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South Australia worms, flies and lice update - October 2019

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Below average spring rainfall following an exceptionally dry start has limited pasture growth and sheep numbers in much of the State—the South East being an exception. The pastoral region has been particularly hard hit with two poor years resulting in extensive destocking and few if any lambs born. Harvesting feral goats has at least provided a supplementary income for some pastoralists.

Worm egg counts are understandably modest with only the occasional weaner mob or late lambing ewes with significant worm burdens. Not a good year for doing drench resistance trials, but it still pays to check drench efficacy by doing a follow-up egg count 10 days after drenching to see if any worms have survived.

In these enlightened times of recommending the use of double and triple active drenches exclusively, the likelihood of worms surviving a drench is limited. However, the adoption of refugia tactics will ensure the maintenance of a susceptible worm population on your farm and minimise the risk of drench resistance developing.

Refugia involves either not drenching the healthiest 20% of a mob, or returning the mob post-drenching to the paddock they had been grazing for a further week before moving to the next paddock. Either tactic will ensure they take worm larvae or adult worms to the next paddock that have not been exposed to the current drench chemicals. A little worm contamination in the fresh paddock is a good outcome as long as they are mostly “drench sensitive” worms.

The modest worm egg counts during the last month indicate the need for a summer drench in adult sheep may be reduced. All age groups should be checked for worm burdens before deciding on the need for a drench going into summer.

Drier seasonal conditions don’t impact flies and lice so much, and so, vigilant detection of these is always important. Spring shearing provides a good opportunity to monitor for lice and decide whether treatment is necessary. It is better to check 20 sheep periodically in a mob than go to the expense of treating clean sheep.


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