Managing flystrike in sheep

Page last updated: Tuesday, 19 October 2021 - 9:08am

Please note: This content may be out of date and is currently under review.

Strategic chemical application

Blowfly prevention chemicals should be used to manage the risk of blowfly strike when environmental conditions are conducive to fly development and sheep are likely to be attractive to flies. Effective chemical use in the prevention or treatment of flystrike depends on understanding the biology of the blowfly, appropriate choice of chemical and correct application.

All registered products used to treat blowflies in a mob scenario (flock treatment) belong to one of three groups:

  • insect growth regulators (IGR) affect growth of immature stages by preventing external skeleton formation, does not kill adults and takes a couple of days to kill maggots, for example cyromazine, dicyclinil etc
  • macrocyclic lactones (ML) — affect the nervous system of insects (kill on contact) for example ivermectin
  • spinosyns — affect the nervous system of insects (kill on contact) for example Extinosad.

Applying chemicals

Of primary importance when applying chemicals is the need to ensure that the correct dosage for weight of the animal is applied by calculating the dose according to the heaviest animals in the mob.

It is important to consider wool withholding periods for shearing and meat and export slaughter intervals when applying a chemical.

The period of protection will depend on what chemical product is used. For more information on specific chemicals please download the chemical table for flystrike control document in the side menu.

Chemical treatment at marking

Applying a chemical application to the breech of lambs at marking may be beneficial in reducing breech strike incidence when wound healing from marking is taking place and through until weaning or first shearing.

Diazinon (OP) is no longer registered for flock treatment but can still be used for individual animal treatment of struck sheep. (Be aware that widespread resistance has been reported in blowflies.)  Extinosad® gives a limited period of protection on lambs as it relies on lanolin for binding and retention. As lambs have less lanolin compared to adults, binding is reduced. Breakdown of applied chemical is also aided by the open hairy nature of lamb fleece as it allows greater exposure of chemical to sunlight resulting in quicker breakdown.

When mulesing with pain relief consider using a preventative fly chemical that has a low volume dose required to avoid or minimise any wash-off or dilution effect that might occur when it is applied over the pain relief chemical.

Chemical treatments for flies can be applied using jetting equipment, hand-wand or by a spray-on method. Traditionally, either an automatic jetting race (AJR) or hand-jetting have been the more commonly used methods of application of preventative fly treatments. However, some IGR products are available as a spray-on application such as Vetrazin Spray-on® and Clik®.

Occupational health and safety

It is important that the product safety label is read and followed. You should also obtain the Safety Data Sheet (SDS, previously called a Material Safety Data Sheet) from your reseller for all chemicals that you use. Due to the likelihood of spray and splash occurring when jetting, wear waterproof long pants, steel capped gumboots and long sleeved waterproof gauntlets. Thin, inexpensive cotton gloves worn inside the gauntlets make the gauntlets easier to put on and take off.

When using concentrates to prepare the jetting fluid, wear a respirator and face shield for protection from fumes and splash. After use, this equipment should be washed, dried and stored safely. Soap, water and a towel should be available to wash off pesticide splashes, as well as clean clothes to change into at the end of jetting or during jetting if contamination occurs.

Withholding periods

Withholding periods require consideration when choosing a chemical and these include the wool and meat withholding periods and the export slaughter interval. The wool withholding period is the time between application of the chemical and when wool is harvested from the animal. The meat withholding period is the time between application of the chemical and slaughter for meat products. The export slaughter interval (ESI) is the period that must elapse between chemical application to livestock and their slaughter for export.

Do not misuse chemicals

Misuse of chemicals can have serious consequences. An unregistered chemical may be ineffective with their use encouraging the resistance development, causing residues and adverse side effects on livestock. Chemicals should only be applied according to label instructions. Using a firefighter to apply chemical is an example of misuse of chemical. With such an application there is little control of how much chemical is applied to individual animals.  Some animals may receive insufficient chemical resulting in ineffective treatment, while others receive substantially more chemical that will result in wool residues present at wool harvesting.

Blowfly chemical table

Choice of chemical will depend on whether treatment or prevention is required, withholding period restrictions, protective period, cost and compatibility with pain relief chemical applications where these are required.

The blowfly chemical table document, in the side menu, outlines details of the current registered products for mob treatment that have no reported resistance to blowfly.

Contact information

Julia Smith
+61 (0)8 9368 3449