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Fogging fungicides offer drench-free future

Quality Management

Fogging with post-harvest fungicides promises to slash the handling of fruit heading into storage, reducing labour costs, fruit damage, cross contamination risk and environmental waste while also lifting the quality of room outturns. 

Pros 

  • Fruit goes straight to coolroom – less forklift handling. 
  • No late-night drenching or wet floors. 
  • No wet fruit into coolrooms. 
  • Fruit can be rapidly cooled earlier (improving storage outcomes). 
  • Eliminates risk of cross contamination. 

Requires 

  • Dry fruit. 
  • A well-sealed room. 
  • Specialist equipment. 
  • A trained operator to carry out fogging.  
  • A door with ports in it to either take the fog in, or to take the cables powering machinery inside the room out. 

In contrast to drenching or dipping fruit for common rots and moulds and to control superficial scald prior to moving into storage, new foggable formulations of fungicides and diphenylamine (DPA) can be applied in the coolroom or controlled-atmosphere room and, in the case of Actimist, can be applied in tandem with AgroFresh’s storage management tool 1-MCP (SmartFresh™). 

Removing a step in the process also allows for earlier cooling of fruit for better quality outcomes. 

Both AgroFresh’s ActiMist™ and Colin Campbell Chemicals’ ecoFOG® products are now registered by the Australian Pests and Veterinary Medicine Authority (APVMA), commercially available in Australia and have had a few seasons to identify any issues and fine-tune processes. 

Colin Campbell Chemicals’ Research and Development Manager Geoff Derrick and Technical Development Manager at AgroFresh Amrit Pannu were at the recent APAL Tech Symposium to provide an overview of how fogging differs from traditional post-harvest drenching, how the two processes differ from each other and what is required for those considering ditching drenching. 

Geoff said ecoFOG was ‘a game changer’ that, as well as being highly effective, reduced labour requirements and eliminated the need to dispose of drench solutions. 

“It seems very, very silly to actually have to go and drench fruit and then put it in a room to treat it with 1-MCP,” he said. “Why not do 1-MCP and fungicides and DPA, if necessary, at the same time? 

“We now have a situation where we can take fruit straight from the orchard and unload it straight into the room ready for post-harvest operations, reducing orchard-to-store time. I think thermofogging, with its ease of use and efficacy, will take over from drench in the next few years.” 

Colin Campbell Chemicals started ecoFOG trials in Australia in 2015 after seeing the process in the United States and in 2022 treated over 100,000 bins. 

AgroFresh launched ActiMist in 2022 across a number of regions and expanded in the 2023 season to treat 65,000 bins. Amrit said AgroFresh had had very promising results from 2022, with good control of rots and significantly improved packouts. 

Both products use the active ingredient pyrimethanil (160g/litre), which is registered in Australia for control of mould caused by Penicillium and Botrytis spp and bull’s eye rots caused by Neofabraea spp within 15 days of harvest. 

“It has been used on grapes for some time, but it’s a new chemistry on apples, which means it’s really a major tool to manage resistance,” Amrit said. 

But both said they were looking at developing alternative fungicides for fogging to spread the risk of resistance. 

The MRL for pyrimethanil in Australia at 15mg/kg is consistent with most global MRLs including that for CODEX. 

Rolling out the fog 

Both products deliver fog with a droplet size of around a micron, which disperses well throughout even a tightly packed room penetrating bins to reach all the fruit, even that in the middle and bottom of the stacks. 

Both Amrit and Geoff presented data demonstrating consistent levels of pyrimethanil throughout the stacks and bins (Figures 1 and 2).

 

Figure 1: The smaller droplet size of ActiMist™ improves distribution throughout the room, allowing for better penetration in the stacks, including middle and bottom bins, which increases shelf life of fruit.

 

Figure 2: After ecoFOG® treatment, data demonstrates consistent levels of pyrimethanil throughout the stacks and bins, particularly when the top layer of bins are covered.

 

Field heat needs to be removed to avoid condensation. Fruit directly in front of the fogging equipment should be covered to avoid potential higher residues at the entry point of the fog into the room. In the case of ecoFog, bin caps should also be placed on the top bins to ensure this more exposed fruit does not receive excess treatment. However, this step is not required when using ActiMist due to the smaller droplet size. 

While ecoFOG and Actmist are both fogging applications of fungicide, there are a few differences between the two product applications. Both require a well-sealed room, specialist machinery, a trained operator and an access door or port into/out of the room. Fans are turned off during the application. 

For ecoFOG, all the machinery sits outside the room, with fog delivered through a pipe into the room and a waste pipe (with a filter) required to manage room pressure.

“The reason being is that we’re actually pumping air in with our fog so we have to equalise the pressure inside the room, so we don’t pop the room,” Geoff said. “We do that with a hose coming out through a regulator so that we know what the pressure differences are. It then goes through a filter, so only clean air is released into the rest of the area. 

“It is a thermo fog. It goes into the room at a high temperature, it rises, rolls across the top of the bins and then, as it cools, it settles down through all the fruit and all the bins. It is a true fog and it gets around all the fruit in all the bins.” 

Geoff said the fungicide could be fogged onto the fruit before or after a 1-MCP application. 

It took approximately an hour to fog a 500-bin room with both fungicide and DPA with a large machine – small machines take a little longer. Rooms were then left for 5–6 hours for the fog to fully settle. 

“In a day and a half, fogging just fungicide, we did 6,000 bins in 11 rooms,” Geoff said. 

Although ventilation of the room is not required, Geoff said due to the CO2 build-up from fruit respiration, pumping air in before restarting CO2 scrubbers was recommended in order to remove as much CO2 build-up as possible. 

In terms of cost, Geoff said fogging was charged by the bin, and estimated it was comparable to the total costs involved in drenching. 

“If you compared the cost of ecoFOG with the cost of drench fungicides only, ecoFOG is more expensive,” he said. “But where it balances out is the huge reduction in labour and moving bins about.”

 

ActiMist is applied using a compact machine that is placed inside the room, with a port needed in the door for a power cable. The unit is also connected to the internet to allow remote monitoring and control of the application.

 

It can be applied simultaneously with SmartFresh, using the same SmartFresh ProTab technology that has been established for years in Australia. As there is no air introduced into the room, condensation is eliminated and there is no venting required from the room.  

Amrit showed a video of a room filling with ActiMist in just 10 minutes. Treating a 500-bin room with ActiMist would take approximately 3 hours. When treating simultaneously with SmartFresh the room needs to be closed for 24 hours as required for the SmartFresh treatment. However, as the application is monitored remotely, a staff member is not required to stay for the duration. 

AgroFresh recommends leaving the room sealed for 8 hours for the fungicide to fully disperse. Refer to the label for the instructions regarding re-entry into the treated area. 

Other considerations

Although thermofogging has been in use in Europe for over 20 years and the United States for at least 10, it is still relatively new in Australia. 

As both require specialist machinery and operators, availability of the technology when it is needed will be key in the early years of uptake. The units are very expensive and technical expertise is required to prepare and set up the equipment for application and it’s a stepwise process to follow all checklists for correct dosage and application. A dashboard is used to monitor flow rate, product applied, and heating block temperature to ensure the application operates to specification. Should there be issues with the equipment, the operator will need to resolve them immediately.  

If there is an issue with the ecoFOG machine, application can be shut down, the machine replaced and then fogging continued without reopening the room. 

AgroFresh has been intentionally slowly ramping up this service to the industry to ensure that the logistics are smooth and that customers have a positive experience.  

Fruit needs to be dry. Geoff said there had been some issues with wet fruit with fogging DPA. “We like to have dry fruit going into the room if we are fogging DPA, otherwise you can start getting issues. But, properly managed, it’s not a problem.” 

Grower experience 

Early adopters of both ActiMist and ecoFOG, Goulburn Valley grower Andrew Plunkett, Plunkett Orchards, and Bill Parker, manager of fruit storage coordination, Jeftomson, shared their experiences of fogging fungicides over the past few seasons. Both said they now fogged 100 per cent of their fruit and would not be going back. 

“It’s changed the way we handle fruit,” Bill said. “When fruit is coming in, we are getting about 1,000 bins/day. Before, it would be off the truck onto the ground, up onto the drench, through the drench down onto the concrete, let it drip dry, pick it up again to take it to the room, and then it’s away. It’s so labour intensive and all the movement is damaging the fruit. This other way, we are just off the truck straight into the room and then we fog with either DPA or DPA and fungicide. Just on labour, it saves a heap.” 

Andrew said the labour-saving had been a saviour when facing Covid-related labour shortages. 

“I don’t think we could go back to doing it the way we were doing it in terms of finding extra people to work at nights and the extra equipment,” he said. “We’ve got used to this being the new way and we only want to handle fruit once.” 

Andrew said they had started with doing a few rooms, building up over a couple of seasons to 100 per cent. 

An additional benefit, Bill said, was eliminating the risk of DPA contamination of fruit moved between sites for drenching. 

“We’ve got two sites that are DPA-free,” he said. “We can actually just fungicide the fruit in the room and don’t have to take to another site to fungicide it over the drench and then take it back. It’s been a blessing in that regard.” 

It’s early days, and rooms of hail damaged fruit from last season are yet to be opened, but early results have been promising. 

“From what we’ve opened up over last few seasons, we’ve been happy with the results,” Andrew said. “There’s still rot that comes up in some lines, but it’s definitely mild, and as good a result as we would expect from drenching.” 

Further reading 

“Thermofogging fungicides into coolrooms”, AFG winter 2022, https://apal.org.au/thermofogging-fungicides-into-coolrooms/  

 

For ecoFOG®, all the machinery sits outside the room, with fog delivered through a pipe into the room and a waste pipe to manage room pressure. 

 

This article was first published in the Spring 2023 edition of AFG.

 

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