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South Australia worms, flies and lice update - December 2016

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Summer has arrived with a few hot days interspersed with mild conditions and so shearing and harvesting have progressed with few interruptions. Occasional rainfall has meant that some green still exists in paddock feed in the 500 mm and above rainfall areas. Abundant dry feed following a good spring has a corresponding high grass seed content, as evidenced in the eyes, ears and skin of sheep across the State.


Worm egg counts (WEC) during November/December have generally been high enough to warrant summer drenching, and so relatively independent of the amount of dry feed available to grazing livestock. Individual counts exceeding 20,000 eggs per gram of faeces have been recorded with Haemonchus (barber’s pole worm) evident in some mobs on lighter soils. While such high counts are usually associated with Haemonchus infestations, it is important to use larval culture on the dung samples to confirm the type of worm present. This is essential to determine the optimum treatment chemical as well as the relative risk of production loss and future preventative measures.

High WECs have also enabled drench resistance tests to be conducted. These have revealed resistance to most of the commonly used chemicals including moxidectin and highlighting their value in determining which chemicals are going to provide the best worm control in respective flocks. Triple-active drenches are a preferred option for worm control, with rotation between effective chemical groups used in specific situations. This is an essential resistance control strategy that all sheep graziers should be incorporating into their worm control program.


The late spring/summer rain and associated warm to hot conditions have also created an ideal environment for flystrike. Scours associated with elevated worm burdens have further promoted fly activity and strike risk. Most adult sheep and replacement weaners are jetted during spring to minimise the risk of flystrike, but prime lambs remain a susceptible class of stock that need to be monitored.

Monitoring worm burdens should continue in January/February to ensure there are no surprises in the New Year. Let’s hope seasonal conditions and red meat prices remain favourable in 2017.

For December 2016 state outlooks, please follow the links below:
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