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South Australia worms, flies and lice update - February 2021

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

The state has been fortunate to experience relatively mild weather in recent weeks and 20–30 mms of rain in late January germinated some green feed across agricultural regions — albeit often only annoying summer weeds in crop stubbles.

Recent monitoring has revealed significant worm burdens up to 3000+ eggs per gram in lambs in the south east, as well as Haemonchus burdens in the Murray Mallee and Fleurieu peninsula. The latter infestations in adult ewes most likely triggered by the rainfall in January. Haemonchosis in summer seems to be a more regular occurrence as unexpected rainfall events, especially incursions from northern Australia, sporadically drop in during our dry period. The ability of lighter, sandier soils to hold this moisture in the topsoil is also advantageous to developing barber’s pole worm larvae. Regular monitoring is the only way to be sure to detect these issues before they cause production loss and so complacency about worm control is an ever-present risk.

Confinement feeding is another worm risk, as confinement means stress combined with concentrated soil contamination and potential close grazing of that soil, even if out of boredom. A worm egg count (WEC or WormTest) check prior to confinement is recommended and a clean-out drench if a significant count is detected.

Questions are already being asked about pre-lambing strategies, such as the use of drench capsules and the need for a primer. The use of capsules pre-lambing is not part of the WormBoss strategy, but since it has been the practice for some years and is gaining popularity, especially in the south east, it cannot be ignored. Anecdotally some producers have used capsules pre-lambing for many years without a significant impact on drench resistance. Superficially this seems the equivalent of hitting a tack with a sledgehammer, but if it removes worm risk during lambing and the lambs and ewes go on to weaning with good growth rates and no dags it is a compelling argument. WEC monitoring should ideally be used to assess the need for a pre-lambing drench and preferably short-acting combination drenches used where indicated. If capsules are used, then a priming dose with a combination drench (and different chemical actives to that in the capsule) is recommended to minimise the risk of drench resistance being encouraged. Otherwise, the risk is of putting too much reliance on the chemical(s) in the capsule to eliminate worm burdens and maintain low WECs for the duration of the capsule activity. It is always important to note the withholding period (WHP), commonly 125 days, for the capsule as well.

The other consideration at this time of year is the importance of planning your paddocks for lambs to be weaned into. We know that worm larval pasture contamination that contributes to the winter worm build-up begins in later summer/autumn and so preparing low-worm risk paddocks begins now. Ensure minimal pasture larval contamination by either shutting up weaner paddocks for three to six months before weaning or only grazing livestock on the paddocks that will not deposit significant worm egg burdens. These criteria restrict grazing to either adult cattle or adult dry sheep that have been drenched prior to grazing with a cocktail of effective drench chemicals. Three months is sufficient if the preparation time falls in hot regions over summer, but for cold areas through winter, six months is needed as worm larvae die more slowly when it is cool.

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