The advent of controlled atmosphere storage has extended the apple and pear marketing season to a 12-month affair. This, of course, requires good control of superficial scald and fungous disease.

These operations have historically been applied by plunge dips or drenchers, with the problems of additional forklift handling with potential damage to fruit, wet floors, late nights spent drenching, wet fruit into store, additional labour costs, risk of contamination of fruit by bacteria that can build up in drench tanks, and, of course, the perennial problem and expense of disposing of the waste drench solution.

Colin Campbell Chemicals (CCC) have supplied DPA and fungicides to drenchers since 1990 but have been determined to find an easier method to apply these products.

Product development manager for CCC, Geoff Derrick says from now on these problems do not need to occur. “Just pick the fruit, stack the bins directly into the cold rooms and ring our operators to come and fog DPA and/or fungicide directly into the rooms.”

Over the last six years, Colin Campbell Chemicals has adopted the US technique of fogging from leading postharvest company Pace International LLC, using specialised fogging equipment and dedicated formulations, including a molecule that is new to postharvest fungus control in pome fruit.

“This equipment uses the thermal fogging principle instead of a combustion principle as it does not introduce excess carbon dioxide (from combustion of LPG) and any other impurities into the room.

“Already we have treated over 60,000 bins of fruit in Australia, and nearly five million bins have been successfully thermofogged in USA, Canada, South Africa and Chile since the process started,” Mr Derrick said.

Thermofogging is compatible with 1-MCP (Smartfresh) and can be applied straight after or before an application of 1-MCP. Thermofogging should be carried out within 7–10 days of harvest, and this fits into the timing for 1-MCP which is within seven days of harvest.

As such, 1-MCP and thermofogging are not mutually exclusive and even go hand in hand, with the thermofogging operation following immediately in the 24 hours after the 1-MCP is added to the room, Mr Derrick said.

The process of thermofogging is carried out by trained operators and there is a large checklist to be observed to ensure that fruit is in the best condition to be correctly thermofogged. It requires specialised machinery and specialised formulations of DPA and fungicides.

The pyrimethanil fungicide (Campbell ecoFOG-160 PYR Fungicide) and the DPA (Campbell ecoFOG-170 DPA Scald Inhibitor) are now registered for use. Pyrimethanil fungicide is a very stable fungicide and will persist for the length of the storage period.

“It’s a fungicide that is looked upon favourably by authorities that set maximum residue levels in each country, as shown by the size of the MRL granted. The MRL for pyrimethanil in Australia at 15 mg/kg, is consistent with global MRLs (EU, CODEX and USA). The product is registered in Australia for control of Penicillium spp, grey mould (Botrytis cinerea) and bulls eye rots caused by Neofabraea spp.

“Even with the room tightly packed, the fog is able to penetrate around all the fruit in all the bins, with adequate residues deposited on fruit whether the fruit be in the top, middle or bottom bins of the stack.

“It takes us less than one hour to fog a 500-bin room with DPA and fungicide. We have demonstrated that we can easily keep up with harvest rates, with a rate of fogging far faster than that of drenching,” Mr Derrick said.

“In one facility, we fogged over 6000 bins in 11 rooms with fungicide over one and a half easy days. I reckon this will take over from drenching within a few years.”