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South Australia worms, flies and lice update - September 2015

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

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

Despite the prolonged threat of El Nino, rain continues to come in dribs and drabs sufficient to keep hopes alive of a good harvest on Eyre and York Peninsulas plus the mid and upper north and Murray Mallee. This follows on from an exceptional early break in the upper north that has that region experiencing a one year in ten season. The season has remained tough in parts of the mid and upper south east where stock feed has not been abundant at any stage this year. However, the reduced rainfall has suited the areas prone to inundation in the lower south east and on Kangaroo Island.

Worm counts have risen over the last month with counts in several mobs across age and breed exceeding 1,000 epg on the Fleurieu peninsula and mid north. In most cases this reflects a combination of an extended period since the last drench and build up on green pastures over the last 6+ months.

Correspondingly, lice and flystrike are becoming more apparent with increasing wool length and the onset of spring temperatures.

As weaning proceeds it is timely to review worm control programs and drench efficacy. A pre-weaning count of 250 epg plus is ideal to check for drench resistance by performing a worm egg count reduction test on lambs around weaning. While time consuming, this process provides an ideal opportunity to establish the optimal worm control program for the next two to three years. Repeated use of any drench chemical inevitably leads to drench resistance and so drench rotation at least annually combined with periodic checks on drench efficacy is prudent to extend the usefulness of these chemicals as long as possible.

Resistance to our most recent new chemical, Zolvix®, has recently been reported and highlights that no chemical can avoid this consequence of frequent use. See your animal health adviser for further details if you haven’t performed a drench test previously.

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