Flystrike season usually runs from December to March but in warm, humid weather can go right through to June. Flies lay their eggs in wool and the maggots that hatch begin to eat the sheeps flesh. This can happen very quickly in warm weather so sheep need to be checked daily. Signs to look for include dark patches of wool, itchy or irritable sheep that get up and down a lot, nibble their wool and stamp their feet. In the late stages the sheep become depressed, stop eating and seek shade. The secretions of the maggots can cause ammonia poisoning days after the first maggots hatched.
Prevention
Shearing will prevent flystrike for a few weeks, although any shearing cuts will attract flies. Keeping the wool short over the summer months, especially the back end is important as long wool easily stays damp and dirty attracting flies. Good worm control is also important to prevent soiled wool attracting flies. Shearing in November/December will ensure wool is short coming into the risk period. Chemical prevention can then be used 4-6 weeks later so the wool is long enough to hold the insecticide.
Insect growth regulators are an excellent long term preventative. They kill the maggots, interrupting the lifecycle which eliminates the adults eventually.
Cyrex is a concentrate that can be diluted in a backpack sprayer and applied to all the wool liberally to saturate the fleece to skin level. This gives up to 12 weeks protection. It can also be used to treat existing strike.
Clik is a spray on that is applied to the high risk areas (crutch and back line) and gives up to 18 weeks protection.
Treatment
It is important to clip any affected areas down to about 5mm and protect exposed skin with sunscreen like Filtabac. After this, an insecticide can be used such as Cyrex, Strike powder or Maggo.