Sheep producers are being advised to consider their strategies when managing and preventing flystrike as the threat of an arduous fly season lies ahead.
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And industry experts are urging producers to "understand dicyclanil resistance" in order to achieve the longest period of protection possible whilst being proactive rather than reactive.
A recent AWI sponsored study, in conjunction with the NSW Department of Primary Industries (DPR), tested all the major blowfly preventative chemical groups to determine their blowfly resistance profiles.
From all the submissions received across Australia, 73 per cent showed resistance to both dicyclanil and cyromazine, whilst a further 15pc of submissions showed resistance to cyromazine.
But Elanco technical veterinarian, Dr Rick White, said the study has unfortunately caused misconceptions about dicyclanil to producers and dicyclanil, when used properly, is still most likely to be the best form of defence.
"Resistance is a predictable feature of modern farming. But the concern producers may have from the recent study is that when resistance is confirmed, then the active cannot be used in future," Dr White said.
"The main misinterpretations would be that resistance means the product won't work at all, or it will always result in a drastically reduced protection period.
"But that is just not true. What we know about dicyclanil is that it is still the chemical that will provide the longest active prevention for the majority of producers.
"It is critical to understand and manage dicyclanil resistance to ensure effective fly control."
Dr White is urging producers to view the data in "full context" as well as making the move to treat flies early in the season, which means now.
"A lot of work has been done to educate producers to not wait until they have fly pressure to get chemicals on," Dr White said.
"If they allow the fly pressure to build up, they have created a reservoir of flies to continue breeding for the rest of the season.
"Early season treatment, before the flies build up, is key to managing blowfly strike by reducing the fly pressure later in the season.
"It is critical producers get this right."
Blowfly strike is one of the most economically significant endemic diseases in sheep flocks in Australia.
It is estimated blowfly strike costs the Australian sheep and wool industry more than $324 million a year in prevention, treatment and production costs.
Dr White said as the largest supplier of dicyclanil products through its CliK family, Elanco has been at the forefront of monitoring and managing resistance since it was first detected in the 2010/2011 fly season, now over a decade ago.
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And as part of Elanco's routine service, they investigate all reported cases of loss of efficacy including, where appropriate, wool testing of residual chemical levels and resistance testing of collected maggots.
"Any reduced protection period should be investigated," Dr White said.
"Resistance reduces the protection period, but so do many other factors.
What we know about dicyclanil is that it is still the chemical that will provide the longest active prevention for the majority of producers.
- Dr Rick White
"We've found that any reported reduction in protection period is rarely, if ever, caused by one factor alone.
"Resistance does not stop the chemical working. rather it reduces the achieved protection period. If you are getting a reduction in the protection period, for example less than the maximum 29 weeks for CliK Extra, get it investigated and find out why - it may not be resistance."
He said often some combination of high rainfall, fly pressure, complicating skin and wool conditions like lumpy wool, resistance and application error are usually the cause of the so-called loss of efficacy cases.
He said application technique and dosage is vital to optimising the protection period.
"Read the label, make sure the dose is right for the body weight of the sheep, and then get the right pattern - put the right amount of chemical in the right place at the right time," Dr White said.
"This is really important in making sure it is in the place where the sheep are susceptible to being struck.
"We as an industry need to continue to be responsible and monitor for any chemical resistance, but planning well in advance to reduce the susceptibility of sheep through genetic selection and management, selecting appropriate long-acting chemicals and applying them properly early in the season will help to ensure we get through the season."
