GREG Richards dipped Merino wethers through his automated cage plunge dipping system, near Glenthompson in Victoria.

The recent announcement by the Australian Pesticides and Veterinary Medicines Authority (APVMA) of the suspension of the registration of five diazinon-based sheep jetting and dipping products will come as no shock to most people involved with the Australian sheep industry.

The problem is the danger to the people dipping the sheep, at least by conventional plunge and shower dipping.

Dealing with lice in the immediate future will not be easy.

Diazinon-based products for jetting and dipping sheep have been under a cloud since comprehensively failing Operator Exposure trials in 2004.

APVMA’s suspension of the jetting and dipping registrations for Di-Jet from Coopers; Di-Shield – Jurox; Diazinon – Western Stock Distributors; Jetdip – Virbac and Diprite from Captec will not affect producers’ use of stocks of these products currently on retailers’ shelves.

There is a two year grace period during which stock can be sold and used in accordance with the current label.

A rush to stockpile product by users will see stocks disappear even more quickly.

Out in the sheep yards, the loss of diazinon will have almost no effect on protecting sheep from sheep blowfly (Lucillia cuprina) strike.

This is because ‘Lucy’ has developed resistance to diazinon to such a high degree that in some instances, maggot offspring are largely capable of surviving the recommended dose of diazinon.

In the isolated populations of flies where diazinon still has some effect on these maggots, it may still be available for treating struck sheep.

It appears that diazinon-based products will still be registered for use for hand dressing individually affected animals.

Commercial availability is another question but there are more effective chemicals available.

Diazinon’s sole remaining useful role has been as a chemical of last resort in treating sheep for body lice (Bovicola ovis).

Diazinon is still highly effective against sheep body lice: there is no known field resistance. When used at recommended rates in effective wet dips it is the cheapest method of lice eradication, by a mile.

Lice resistance to the synthetic pyrethroid (SP) chemicals is already widespread, and is emerging to the insect growth regulator (IGR) family as well.

Sheep and wool producers with infected flocks should first aim to determine the reason for, if not the source of, the infestation.

Past surveys have shown approximately 70 per cent of lice infestations are a result of ‘carry-overs’ (failure to eradicate), not introductions from neighbours, travelling stock or other sources.

Eradicate – don’t control – lice by shearing all sheep at the same time – ewes, lambs, weaners, rams (often forgotten), and stragglers.

Then treat all sheep in an effective wet dip.

This means plunge dipping. In the short term diazinon will be the chemical of choice, but producers may need to be quick to take advantage of the remaining opportunity.

Dip all breeds; lice might not prosper on some of the newer ‘less woolly’ breeds but they may well survive.

Then quarantine the place; spend the money you used to spend on ‘backliners’ at shearing, on the boundary fence, if that is a concern.

Take particular care with all introductions.

Quarantine them initially if possible: better still shear and treat them immediately on arrival and once again, don’t forget the rams.

Lice detection tests are still a futuristic hope, so the best thing to do is put your specs on and look for lice at every available opportunity.

Contact Ian Evans (03) 5881 9920, 0427 102 287.