Tuesday, 18 December 2018

Foiling the fly


While the warm, humid conditions we have been experiencing lately are great for grass growth and thunderstorms, the bad news is they aren’t so good for your sheep flock.

Being prepared for flystrike whatever the weather may bring is a smart move. With flystrike costing New Zealand farmers millions of dollars in lost productivity each year, fly can strike a significant blow (no pun intended) to the health and production of your sheep flock. Prevention is better than the cure – so having a plan in place is key in winning any fight against the fly.

What’s the best way to prepare for battle?

  1. As the great war strategist Sun Tzu is quoted as saying, one must know the enemy: This means understanding the life cycle of the fly and recognising the conditions they thrive under.

The first wave of attack comes from pupae that have wintered in the soil. They hatch and commence searching for a high-protein food source – aka carcasses or daggy sheep. Each female has the capacity to produce up to 600 eggs in her lifetime, which means when conditions are right, it’s on! Eggs can hatch, mature to maggots, pupate and hatch new flies within 12-20 days.

  1. Know your environment: Dispose of sheep and cattle carcasses by burning or burying. Small mammal and bird carcasses can also become breeding sites and should be disposed of as well. Using fly traps will allow you to better predictor the flystrike risk. Paddocks with scrub and thistles attract flies so try to avoid them where possible. When fly pressure is high avoid ‘hot spots’ where flies congregate such as sheep camps, scrubby gullies and bush margins. Use more exposed, windy spots for grazing if possible.
  2. Prepare your stock: Without food, flies can’t prosper, so the first line of defense is to make your animals unattractive for flystrike. Employ an effective drench programme to reduce parasite burden, regular crutching and preemptive application of flystrike treatments. Ensure poorer or vulnerable animals (those suffering from ailments) are treated and monitored accordingly.
  3. Prevention is better than the cure: Strategic application of chemicals (dips) is critical for flystrike prevention. Just as important as the product is the application method, which needs to ensure a good coverage of the chemical down to skin level over the areas of the sheep most prone to strike, including the shoulders and back, rump and pizzle on rams. The gold-standard is saturation dipping, but jetting can be very effective if a sufficient volume of dipwash is applied. Pour-on and spray-on products are also widely used. The most commonly used chemicals are insect growth regulators (IGRs), namely diflubenzuron, cyromazine, triflumuron and dicyclanil, as these will generally ensure flystrike prevention for up to 12 weeks or more. Other chemicals include the synthetic pyrethroids (SPs), spinosad, imidacloprid and organophosphates (OPs).
  4. Two pests, one product: Many of these chemicals also control lice and it is becoming more common to use combination products, both for fly and lice control. Most combination products include an IGR with another IGR, an SP, spinosad, imidacloprid or an OP. IGR-resistant fly strains do exist, so using combinations will control these and delay the development of resistance in susceptible strains.

If in doubt, seek expert advice on the appropriate dip chemicals to use, along with the correct application method and timing.


Chemical Group

Active Ingredient

Application method/s

Meat, Milk Wool WHP days

Cyromazine Spray On IGR Cyromazine Spray On 7,35,60
Cyromazine Liquid IGR Cyromazine Plunge, CR, Jetting 7,35,60
Saturate® Gold


Plunge, CR, Jetting 10,35,60
Saturate® Classic IGR Diflubenzuron Plunge, CR, Jetting 7,35,60


Diflubenzuron Pour On Nil,35,60

IGR=insect growth regulator, SP=synthetic pyrethroid, CR=constant replenishment shower dip