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South Australia worms, flies and lice update - March 2018

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Significant rainfall in late November has been followed by nearly four months of exceptionally dry warm to hot weather with even Adelaide only recording 6 mm of rainfall to late March, 2018. This would not be considered conducive to worm survival, but worm egg counts across South Australia over the past month indicate two in three mobs have counts exceeding 100 eggs per gram warranting a “late summer” or pre-lambing drench.

These harsh conditions should have stifled the reproductive aspirations of most worms. However, as the cooler evenings and morning dews start to increase in frequency and intensity any worm eggs are more likely to survive desiccation leading to infective larval stages on soil/pasture for unsuspecting grazing ruminants. There is little pasture or ground cover across the State and so infective larvae have little protection in those situations. However, any moisture in the next month will encourage regrowth in perennial plant species or potential germination of annual species assisting the buildup of infective larvae awaiting consumption by hungry stock grazing close to the ground. As a result, unmonitored or undrenched stock could develop significant worm burdens over the next 4-6 weeks.

That begs the question….is a pre-lambing drench warranted? Recent monitoring of ewe condition and pasture feed on offer during Life Time Ewe Management  sessions indicates ewe condition score has been well maintained – admittedly with significant grain supplement inputs. However, the scarcity of autumn feed indicates decisive action on worm control prior to lambing is paramount. The decision whether to drench should be based on egg count monitoring; ewe condition (ideally mob average = 3); feed on offer (preferably > 1,000 kg DM/Ha); and the intended management of the paddock being grazed i.e. are lambing ewes to remain in this paddock or will it be spelled for several months. 

It is difficult to predict weather patterns at this time of year, but if the rain forecast is bleak and worm counts are 100 eggs per gram or more then targeted drenching is indicated. These decisions need to be made on an individual mob basis using local knowledge. However, it is important to remember if drenching at this time of year to make sure you use an effective drench. If you haven’t done a drench trial recently to establish which drenches are effective, consider doing another egg count 10 - 14 days after drenching to see if any worm eggs remain. At least then you will have a retrospective indication of drench efficacy.

Another consideration is the risk of worm pickup associated with high intensity stocking/grazing i.e. there is usually an increased risk of faecal and hence worm larval contamination of feed provided with trail or confinement feeding. Once again worm egg count monitoring will soon indicate whether a pre-existing worm burden needs to be removed before subjecting ewes to these management strategies in the lead up to lambing and/or the season break.

For March 2018 state outlooks, please follow the links below:
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