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South Australia worms, flies and lice update - September 2014

Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (trengovet@icloud.com)

Spring has arrived all too early with additional rain required statewide to assist crop and pasture yield. The mild sunny conditions through August/September will not have harmed worm contamination on pastures, but lack of pasture growth will have resulted in closer grazing and so enhanced larval pick up for this time of year. In addition, the SOI indicates that we are experiencing the predicted El Niño and so additional rainfall is likely to be diminished.

As per usual there is more variation in worm egg counts within districts than between districts/regions i.e. WECs have had a similar range of 0 to 850 recorded over the last month regardless of whether from Eyre Peninsula, Adelaide Hills or the south east. There are no particular trends at this time of year i.e. egg counts are not reflective of age, sex or pregnancy/lactation status, but more indicative of local grazing and drenching history. The majority of recent WECs have exceeded 200 eggs per gram and so drenching decisions need to be weighed against the condition of the sheep as well as intentions for the paddock currently grazed and those yet to be grazed. 

It is normal for the rising quality and quantity of pasture in spring to naturally limit worm burdens and worm egg output diminishes as spring advances. Frequent WEC monitoring assists decision making about the need for drenches at this time of year i.e. instead of giving a "salvage" drench now it may be preferable to delay drenching and give a "strategic" first summer drench when recontamination of paddocks is much less likely. This strategy would be enhanced by a drier than normal spring/summer if indeed El Niño does persist.