Recent wet weather will make conditions ideal for flystrike once temperatures start to rise.
Moisture is a critical factor in flystrike, as for eggs to hatch and larvae to establish, they need at least 24 hours of moist conditions in the fleece.
The focus of any flystrike prevention programme is to make sheep as unattractive as possible to the four problem blowfly species (Australian green blowfly, European green blowfly, Brown blowfly and hairy maggot blowfly).
An Integrated Pest Management Approach aims to keep pressure on a pest throughout all stages of its lifecycle and uses both chemical and non-chemical tools.
Chemical options
Chemical options include Insect Growth Regulators (these include Benzyl phenyl ureas and Triazine and pyrimidine derivatives), Macrocyclic lactone, Neonicitinoids, and Spinosyn.
To prevent chemical resistance, it is important to rotate different chemical groups if treating sheep twice in a season and use a different chemical to treat an active flystrike lesion to the one used for flystrike prevention.
If using combination sheep dips for flystrike prevention and lice control, consideration should be given to the efficacy of the products used and their resistance status.
Preventative chemicals should be applied before the risk period.
Heavy continuous rain following treatment may impact on the efficacy of the chemicals used. Information about this should be on the product label.
Monitoring
Anticipation is the key to good flystrike management as this allows farmers to take a proactive rather than reactive approach.
Monitoring flytraps, either homemade or purchased ready-made, are an excellent way to predict the on-set of blowfly activity, provided they are checked regularly for green and golden-brown blowflies. Instructions on how to make a cheap flytrap is in the Managing Flystrike and Lice resource book ( link at the bottom of this article).
Husbandry
Specialist forage crops, especially those that are high in tannin, or clean pastures result in less dags and therefore sheep are less attractive to flies.
Shearing and crutching help by reducing fleece moisture and contaminants such as dags, pizzle rot, urine stain and lumpy wool, but flies are also attracted to footrot and blood.
Tails that are either too short or too long can also increase the risk of footrot.
Carcasses will support a maggot population and because strike flies only attack carcasses in the three days after death, dead animals should be buried, burned or put down an offal pit as soon as they are discovered.
Farm hotspots
Some areas of the farm will be more attractive to flies than others. These include sheltered scrub-lined gullies, thistle patches, bush margins, stock camps and the lee of shelterbelts. When fly pressure is high, ideally stock should be moved to more wind exposed pastures which flies don’t favour.
Genetics
There are genetics tools available to increase a sheep’s resistance to body and breech strike. These include breeding values for dags and reduced wrinkles and resistance to fleece rot in fine wool breeds.
Record keeping
Keeping a record of when stock were treated and local weather conditions along with regular stock checks will provide a guide as to whether a flock may need re-treatment.
For more information
- Managing flystrike (PDF, 672KB)
- Managing flystrike and lice (PDF, 5.0MB)