Earlier this year APAL applied to the Australian Pesticide and Veterinary Medicines Authority (APVMA) for the emergency use permit due to unusual wet weather in some regions which offered ideal conditions for Alternaria infections.

APAL Technical Manager, Angus Crawford, also said the application was made when the apple and pear industry had to surrender the seven-day WHP permit – which should have expired in June 2016. “There was a chance that some growers may not have been aware of this change and the emergency use permit accommodated this. Until further notice, growers must follow the 21 day WHP for all dithianon products.”

Research on the Alternaria disease showed that early fungicide applications during bud-burst, flowering and early fruit development sets up very good control initially. Generally, the regular fungicides that control blackspot are also likely to control Alternaria. Orchard hygiene is essential to reduce inoculum and leaves should be monitored throughout the season for any signs of the disease.

Crawford said, “While growers can set up good, early control the job is far from over and there are certainly no guarantees. Alternaria research shows that under high humidity (>65 per cent), warm temperatures (26-33oC) and summer rains, rapid progression of the disease can occur. Given the right conditions Alternaria can effectively explode leaving growers in difficult situations unable to protect their fruit. This is where dithianon at a seven-day WHP can be particularly useful especially when harvesting varieties requiring multiple picks such as Gala.”

Crawford is currently working with the registrants, CropCare, to determine what residue studies are needed to support this use and reinstate the seven-day WHP. “It looks like four residue studies are needed around the country and a decision on whether or not to proceed with this work is about to happen.”

APAL said it will continue to update industry members as information comes to hand. For more information, contact Angus Crawford, Tel: 03 9329 3511.