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South Australia worms, flies and lice update - October 2015

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

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

Very dry and unusually hot conditions have prevailed in much of South Australia during October and the latter part of September as predicted due to the warm sea surface temperatures off the west coast of Western Australia and corresponding strengthening El Niño.

The early and sustained rainfall in the mid and upper north has enabled a finish to the season despite the hot dry spring, while other parts of the state and especially the mid and upper south east have been less fortunate. A lot of hay has been cut north of Adelaide and there will be plenty required south of highway one. 

Worms generally pay little attention to seasonal conditions at this time of year and counts have been quite variable ranging from zero to 2,000 eggs per gram. If any trend is apparent, generally, the higher counts have been in the higher rainfall areas, but not necessarily related to age or sex. This is to be expected as worm egg counts in spring are largely a result of worm control (or lack thereof) practices over winter. 

It is generally expected that better nutrition in spring will have a moderating or suppressive impact on worm populations and may encourage a drop in worm egg output. However, this can vary from mob to mob and so monitoring is always the best option in deciding the need for and type of worm control strategy. Drench tests are usually completed by now as lambs are weaned and so the choice of the most effective drench is made easy. 

A first summer drench is recommended if counts are above 150–200 epg, but condition score, drenching history, age and intended paddock use are all factors that need to be assessed before deciding on a strategy. 

The need to retain refugia over summer is also an important strategy to maintain a susceptible worm population on the property. This can be achieved by not drenching the healthier looking 10% of the mob if a spring / first summer drench is required, or continuing to graze the paddock of origin for another week after drenching and before moving the mob to a new pasture. If this sounds confusing, please discuss further with your local worm control expert. 

Remember, it is best to monitor instead of assuming a summer drench is required. The plan should always be to minimize summer drenching, but use it if needed. 

Flies were also encouraged by the warm late winter / spring and fly strike caught many producers by surprise during September. The predominance of spring shearing should reduce fly worry as well as jetting, as producers prepare for harvest. 

For October 2015 state outlooks, please follow the links below:
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