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Western Australia worms, flies and lice update - January 2019

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Across Western Australia

Whether or not you managed a summer holiday away from the farm, on most properties, there will still be a holiday from drenching sheep.

Unless there is significant summer rainfall, this is the time of year when sheep should have their lowest worm burdens. Even if sheep carry some worms, the vast majority of any worm eggs dropped onto dry pastures will die quickly, and never reach the larval stage that can infect sheep (or goats).

By this time of year:

  • Lambs (2018 drop, orange tags) and hoggets (2017 drop, white tags) should have received a summer drench, either when on dry pasture or as they went onto crop stubbles.
  • Adult sheep (black tags and older) are due for a drench in March or early April, or if given a summer drench, a percentage should have been left undrenched. Both approaches ensure that some non-resistant worms remain in the flocks, to dilute any resistant worms that survive in sheep given a summer drench.

However, there are a few boxes to be ticked to ensure the best possible worm control:

  • Were summer drenches fully effective? These need to be close to 100% effective, to ensure a good worm kill, and to reduce the survival of any drench resistant worms. Drench resistance is alive and well in Western Australia, and in general, the older the drench type, the less likely it is to do the job.
  • Were summer drenches given at the right time? If some worm larvae were still present on the pasture when drenches were given, sheep will pick up some worms, which may reduce worm control in the longer term. It’s not an issue for sheep drenched onto crop stubbles, but often it is for sheep drenched while on pasture.
  • Are there any green pasture areas? Where perennial pastures survive over summer, worms are a bigger threat than in drier summer regions, and barber’s pole worm is a potential problem. If there’s enough summer rain to freshen up green pastures, there’ll be a bigger risk of summer worm problems.
  • What about summer rainfall? If a germination lasts for even a couple of weeks after summer rains, worm eggs dropped from sheep could develop to the larval stage. It’s not a problem in sheep not carrying worms at present, but you need to be sure. Even small worm burdens can increase and may derail the summer drenching program. Worm larvae die quickly once hot and dry weather resumes, but it’s hard to gauge the risk without checking.

If any of these issues raise queries, the answer is to take worm egg counts to check that worm control is on track. If there is a summer pasture germination, allow 4–5 weeks after the rain before taking dung samples, as it takes time for worms to develop in the sheep.

Hot and dry conditions are bad for worms—but they are survivors, and we need to be sure there are no nasty surprises down the track!


Esperance: Nicole Swan, Swan’s Veterinary Services (

Recently this region experienced some hot weather with more to come over the weekend. Pastures are dry, and the kikuyu could do with some rain. Hopefully, producers have enough summer feed and stubbles available so that weaners and hoggets can be drenched onto them at the summer drench.

Over the next 1–2 months, warm, dry weather will help kill larvae on the pastures. Three months of hot summer weather is needed to classify a spelled paddock as ‘clean’, even perennial pastures (though up to 6 months is needed through winter). Keep this in mind when planning your worm control strategy for the year.

If there is significant rain over the summer months, some scour worm larvae that have been protected from the heat inside the egg shell, inside the faecal pellet, may hatch, but barber's pole worm will barely survive for one week in the facecal pellet. It is recommended that sheep are monitored four weeks after rain to check for worms, especially barber’s pole becasue they favour the warm wet conditions.

Monitoring of worm susceptible sheep—weaners and hoggets and any sheep that are nutritionally stressed—is recommended in late February. These sheep do not always make it through the summer with a low worm burden, and may require drenching before autumn.




For January 2019 state outlooks, please follow the links below:
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