Helping you get the Best Results this Spring:  Tackling Lice, Flystrike and Worms in Sheep

We know spring is a busy season for sheep farmers.

As a result, below we present some quick and easy recommendations for products that will allow you to achieve optimum results in managing lice and worms and in preventing flystrike.

Firstly, we recommend taking a comprehensive look at all the chemicals you are using for all three different issues this year so that you are minimising the chance of resistance developing and maximising the effectiveness of all products used.

Then we recommend the following:

  • Lousicides
    • To prevent resistance, rotate to a different lousicide product on an annual basis. There has been a heavy reliance on Avenge (imidacloprid) and Extinosad Pour On (spinosad) in recent years which creates a high risk of resistance developing in your flock.  So you could swap to Avenge or Viper this year if you have been using Extinosad Pour On, or swap to Extinosad Pour On if you’ve been using neonicotinoids, macrocyclic lactones or organophosphates (see the reference below).  If you prefer the neonicotinoids, Viper is a great product to swap for Avenge this year because it contains thiacloprid which under can be up to six times more potent against sheep lice than imidacloprid.


NeonicotinoidsSpinosynsMacrocyclic lactonesOrganophosphates
imidacloprid (e.g. Avenge)

spinosad (e.g. Extinosad Pour On)


ivermectin (e.g. Coopers Blowfly and Lice)

diazinon (e.g. Eureka Gold)


thiacloprid (e.g. Viper) abamectin (e.g. Coopers Maverick) 


  • If you can’t rotate to a different product this year for any reason, work toward eradicating lice to prevent a resistant lice population developing. Sheep that are treated with a long wool lousicide e.g. Extinosad Lice, Fly & Maggot Eliminator of course must also be backlined with an off-shears lousicide straight after shearing to help achieve eradication.
  • While not an issue at the current time due to the widespread use of dicyclanil (Clik) to prevent flystrike, it is important to note that the same chemical should never be used as a lousicide and as a flystrike preventative in the same wool growing season. This is because lice are present and active on sheep over their entire life cycle, so are present for both louse treatment and any further flystrike preventative treatments later on.  This greatly increases the chance of resistance developing.


  • Worm treatments/drenching
    • Always carry out a Worm Egg Count first to see if worm burdens warrant drenching.
    • If drenching is required, always use a combination “fully effective” drench.
    • There is significant resistance to older chemicals used for the purposes of drenching, including macrocyclic lactones like abamectin (e.g. Coopers Maverick, Virbamec Oral LV, Raiden) and ivermectin (e.g. Ausmectin).
    • Use long-acting worm treatments and use a primer as well as an exit drench during conditions of high worm risk. Primer drenches are a combination product given at the same time as the long-acting drench treatment and contain different chemicals to the long-acting treatment.  Exit drenches are again a combination product using different chemicals to the long-acting treatment.  They are administered two weeks after the end of the long-acting drench treatment period to kill larvae that have survived and developed into adult worms.
    • As usual, quarantine drench all new or returning sheep with a quality fully effective combination drench with preferably four active ingredients including monepantel (e.g. Zolvix Plus) or derquantel (e.g. Startect). Monepantel and derquantel come from different classes of chemical and as a result offer another “string to your bow” in protecting against worms.
  • Flystrike preventatives
    • Dicyclanil products (Clik) are still currently the preferred option for flystrike, however there has been some resistance to this chemical seen in other states, and the widespread resistance to cyromazine (e.g. Vetrazin) is a serious concern.
    • Apply dicyclanil products e.g. (Clik that provides protection for up to 29 weeks) early in the season and as it suits you depending on shearing/crutching times.
    • Don’t use cyromazine products such as Vetrazin.

Finally, always apply each product as recommended on the label to maximise the benefit of each chemical.  Other on farm and grazing management strategies also of course have a significant positive effect in reducing the incidence of flystrike, worms and lice over the longer term.

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