Back to State Outlooks

South Australia worms, flies and lice update - May 2021

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

A state of contrasts where much of the far north pastoral country is green following weather incursions from the north, the cereal growing areas are dry sowing in hope, while parts of the south east have received 50 mm in May on top of good rain through April.

Recent worm egg counts (WEC) indicate a quarter of mobs have needed a drench and some with WEC in the 1000s indicative of Haemonchus burdens. Notably, many of the 200+ WEC were in mixed age pregnant ewes in the sheep cereal zone ie 400 – 500 mm annual rainfall. These pre-lambing WEC are possibly elevated due to the peri-parturient reduction in immunity that occurs in later pregnancy associated with protein being primarily used for lamb growth and milk formation. They also coincide with the moist cooler conditions in autumn conducive to worm larval survival following on from worm egg contamination on pasture during summer. This highlights the need to plan six months in advance when preparing paddocks for the most worm susceptible sheep - lambing ewes and weaners. These paddocks should only be grazed by low worm risk sheep in the preceding six months ie mature sheep with negligible WEC or cattle.

It is easy to opt for administering drench capsules pre-lambing to control worms through lambing to weaning, but this is relying entirely on chemicals to achieve outcomes. Anyone who is farming for the long term will know this is not a sustainable practice as all chemicals eventually fail due to the development of resistance – especially those which stay in the body longest. Sustainable parasite control incorporates a combination of grazing management, frequent monitoring of parasite burdens and strategic use of chemical combinations in rotation. Astute graziers will be aware of the worm risk of various paddocks based on worm monitoring and by keeping a record of their grazing history.  Future grazing can then be planned accordingly.

For May 2021 state outlooks, please follow the links below:
Back to State Outlooks