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Victoria worms, flies and lice update - November 2014

Hamilton: Andrew Whale, Livestock Logic (

Don’t select for drench resistance during the drought!

Conditions in the South West of Victoria remain dry with plenty of lambs now going onto full grain rations for finishing, probably 6 weeks earlier than the previous year. Dry standing feed levels are well below normal years and we would expect the majority of producers to be feeding large numbers of stock early in the New Year.

Drought conditions do have some benefits from a worm management perspective. The lack of carryover feed means that it is a good opportunity to clean your paddocks of worm levels prior to autumn. But it is also an opportunity to heavily select for worm resistance with unnecessary drenching, so we need to make the correct decisions on whether to drench, how many to drench and what product to use.

Do I Need to Drench?

  • Base on Worm Egg Counts. Where counts aren’t reducing production then it is advantageous to delay drenching a few more weeks.
  • There are lower drench trigger levels in summer, as we are concerned with pasture contamination, not just production loss.

Leave a Proportion of the Mob Un-drenched

  • Unless drenching lambs, skinny sheep (

Get the Right Drench

  • Must avoid any long acting products over summer—capsules or moxidectin
  • Use highly effective drenches—new actives or 3-way combinations

Post drought we can often see the emergence of drench resistance on properties that have previously had effective drenches. This is due to overzealous drenching in the summer when larvae levels on pasture are very low. Ensure that the drench is required this summer before selecting for drench resistance.


Benalla: Tricia Veale (

Very warm and dry weather conditions were evident in this area of North Eastern Victoria.

There was only 13mm of rain for the whole of October but a big sudden downpour eventuated a few days ago giving 38mm so far for November.

The paddocks were rapidly drying off and many crops have been harvested, but fortunately, most dams are still reasonably full.

Worm egg counts appear to be at lower levels and the recent rain will allow the immature worms to survive, depending on the future rainfalls.

The purpose of the first summer drench is to eliminate worms inside sheep, as the pasture dries off. If sheep are not drenched at this time, they will continually pass worms eggs that will contaminate the pasture and become the seeds for problems later on. The timing of this drench is important; in most years it’s usually carried out in early/mid December, but may well be needed in late November.

This is the time to make sure that there are no large numbers of worms inside the sheep, as most of the larvae on the pasture will be soon killed by the ultraviolet light and heat of summer. This helps to bring about a natural break in the worm life cycle. So check the situation by getting some worm egg counts done.

Drenching sheep unnecessarily will not only cost you money but hasten the development of drench resistance on your property. This is because you kill all the susceptible worms, so that worm types that have resistance to certain drenches survive in greater numbers.

This is also the ideal time to get a drench resistance test done on your youngest sheep.

Older sheep with a higher condition score have some tolerance to moderate worm infestations. Knowing your drench resistance status is an essential business strategy.

This test should be carried out about every 2–3 years to keep up with the resistance trends on your place.

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