THE PROPOSED national ban on sheep lice chemical diazinon could spell disaster for Australian sheep producers with lice-affected sheep.
The Australian Pesticides and Veterinary Medicines Authority (APVMA) remains firm on deregistering and limiting the use of products containing diazinon despite 30pc of the nation's sheep flock remaining lice-affected.
Diazinon is a broad-spectrum organophosphorous insecticide used widely for external parasite control in wool and has historically been used in the sheep-dipping process to control lice.
Most woolgrowers use a backline to control lice in their flocks but diazinon is regarded as the most effective way of treating lice and breaking chemical resistance patterns.
The APVMA has reviewed diazinon use five times in the past 10 years after scientific research suggested organophosphates could be carcinogenic to humans.
The current review found diazinon posed unacceptable risks to rural workers and could leave chemical residues on horticultural products.
Australian Wool Innovation (AWI) animal health project manager Scott Williams said a diazinon ban would not increase flock lice populations immediately but if growers were forced to rely heavily on insect growth regulator (IGR) backlines it could lead to a rapid increase of resistant lice in the national flock.
Synthetic pyrethroid backlines are considered almost useless for lice control due to high levels of resistance.
Dr Williams said there was further anecdotal evidence of some IGR's showing signs of resistance.
"Going into the future, if we are taking out one of the chemical groups for lice control, it only leaves a couple that are still effective," he said.
"And that places pressure on parasite resistance and residues in the Australian clip."
Immediate contact with diazinon can potentially be harmful to humans but it does break down rapidly when exposed to sunshine and water over a 12-month period.
Wool treated with diazinon 11 months prior to shearing will show little if any signs of chemical residue.
Dr Williams said there was scarcely any resistance to diazinon in lice.
He said about 30pc of the national sheep flock had lice and about 60pc of the entire flock were treated for it.
The diazinon review provided growers with an opportunity to introduce on-farm biosecurity plans instead of unnecessarily treating for lice, Dr Williams said.
WAFarmers is considering a petition for the continued availability of diazinon under special permits for the treatment of lice in sheep.
WAFarmers wool council passed a motion last month to approach CSIRO to establish an Australian Standards guideline for chemical residues in wool, in consultation with wool processors.
The European Union has already established comprehensive guidelines and standards for residues for wool imported into Europe.