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Tasmania worms, flies and lice update - August 2018

Tasmania WormBoss Worm Control Programs

Tasmania WormBoss Drench Decision Guides





Perth: Paul Nilon, Nilon Farm Health (

Since the last missive it’s been wet, cold and miserable, except for the East Coast, which has just been cold and miserable.  I wonder if Darwin needs a sheep vet? Given that the rivers have been too high and dirty to fish, and venturing to the lakes would be like a polar expedition, the tropical option is tempting.

Egg counts submitted in the last month have been almost universally high.  Merino hoggets have been at 500–1000 eggs per gram. Although I often suggest that counts in young sheep be allowed to run out a bit to promote immune resistance, most paddocks these sheep are on are too short to take the risk. Moreover, with water lying everywhere there is a real risk of late winter black scour worm. Apart from knocking the stuffing out of the hoggets, high levels of contamination will reduce the efficacy of the first summer drench in November–December.

Merino ewes are also on the up and up (worm egg count wise). So, as with last month, it may be the year to consider a long acting treatment.

Cross-bred (XB) ewes are for the most part looking robust.

What’s New 1: Name Dropping:  The biennial Paraboss Conference was held in Melbourne on August 17, 2018. A review of worm control A–Z by the brains trust (Brown Besier, Lewis Kahn and Angry Webb-Ware) showed there is really nothing new, but they highlighted a few things that I tend to bang on about till I am tired and you are sick of hearing. These include, but are not limited to:

  • Use long acting drenches sparingly. They promote resistance.  When you do have to use them consider both priming and tail-cutter drenches to reduce the chance of additional resistance.
  • Use Integrated Parasite Management (IPM): use a number of control strategies together, including reducing contamination on paddocks by appropriate spelling or alternative grazing. This means that all Merino producers should consider smart grazing to provide low-worm winter grazing on perennial pastures.
  • Monitor diligently to reduce the need for drenching, and importantly, to drench before everything goes to shit (literally). This means monitoring Merino weaners every 3 weeks.  Otherwise, talk to me about plan B.
  • Use combinations (of drench actives), particularly if all of the components are working OK (greater than 80%).

If you need more information spend some time on the Wormboss website.

What’s New 2:  Computer Models: I’ve had an ambivalent relationship with models ever since Elle left me standing at the altar. Notwithstanding, they are increasingly a part of our decision making.

Complex models are a bit like a junk-food diet:  if you put rubbish in, what comes out may be a powerful class of ugly. Further, it becomes harder to intuitively verify the results with your experience.

Tasmania’s own Brian Horton presented on two flystrike models of which he is the chief author. Although the modelling algorithms must be immensely complex, the inputs and outputs are simple enough to give a deal of confidence.

The FlyBoss Tools use historical weather data to predict your flystrike risk in an average year given various shearing and treatment times.  The tools are simple to use and are a good starting point to plan your annual fly control strategy. Sometimes simple tweaks (e.g. moving shearing time or treatment time by a few weeks) can make an enormous difference to strike risk.

The flystrike component of AskBill is a corker. AskBill is an enormous undertaking by the Sheep CRC. With quite limited inputs you can get a series of predictive results on nutrition, and the risk of flystrike and weather losses. The flystrike component uses Bureau of Meteorology (BOM) weather predictions out to 6 months to plot the risk of fly events compared with the risk against long-term weather data. If you think that the BOM's long term forecasts are wobbly, Brian demonstrated that at 1–2 months they are very robust, and even at 6 months they are more robust than using average historical data. Importantly, AskBill will send alerts if the fly season looks like being difficult. AskBill is currently being commercialised, so check out the cheap subscription price and give it a go.

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