—by Kate Prengaman

Several years ago, grower Jason Matson started to wonder if the decay problems Matson Fruit was dealing with could be caused by cross-contamination from the recirculating fungicide drencher at his warehouse.
“The first ones (bins) through are great,” he said. But over 600 bins, the recycled water accumulates bits of soil and sod that the forklifts pick up, as well as any pathogens that might have been lurking on the fruit. “The last ones get all the crap.”
So, he rigged up an alternative approach to use a single pass of water. In the orchard, tractor drivers haul each single-tier bin trailer under a fungicide rain shower station before loading trucks to the warehouse.
Once he dialed it in, he invited researchers from Washington State University to study its performance in terms of coverage, rot control and food safety.
“Our standard is ‘as good as the warehouse drencher,’ otherwise why would we do it?” Matson said.
The research team — pathologist Achour Amiri, extension specialist Gwen Hoheisel, and food safety specialist Claire Murphy — found that indeed, it does outperform the Matson warehouse drencher they used for comparison, particularly on the food safety front. Their work was funded by the Washington Tree Fruit Research Commission.
Perks of single-pass water
Any time recirculated water is used, there is potential for cross-contamination, Murphy said. That’s why the researchers were excited for the opportunity to study Matson’s novel approach.
For the food safety trials, they compared apples before and after treatment, looking for the presence of any coliform bacteria and generic E. coli. While not pathogens themselves, they are indicator species.
“Indicators show that we are creating an environment that could be cross-contaminating those pathogens,” Murphy said.
Across two seasons of trials, they found that most (75 to 95 percent) of the apples harvested were free from coliforms and, after the single-pass application, there was no change, indicating no cross-contamination. On the other hand, after the warehouse drench, coliforms were detected on almost all of the apples tested.
The E.coli findings were similar but less stark. Before treatment, over 96 percent of the apples had no detectable E.coli. After the field application, 98 percent of the apples treated with the single-pass remained free of E.coli, but only 93 percent of those treated with the recirculating drencher were.

So, the findings show significant cross-contamination by the warehouse drencher, but that doesn’t necessarily mean it’s a big risk, Murphy said. The industry’s standard storage practices have been shown to reduce the presence of foodborne pathogens.
Rather, the findings provide insight into the importance of considering the food safety risks throughout the postharvest chain and managing them in ways that will reduce risk, such as regular cleaning of the drencher or incorporating sanitizers into recirculating water, when possible, she said.
That’s the clear takeaway for Matt Miles, the research and development director at Allan Bros. Fruit and a member of the research commission, who is familiar with Matson’s single-pass application design and the research.
“Everyone needs to clean their drenchers between batches. It makes no sense to recharge,” he said. “This is something we should all be doing to lower the risk of a drench. … If we do industry best-practices on how we control our dump tank water and other practices on the packing line, the product is safe.”
Decay pathogen findings
Just like on the food safety front, the research showed that the recirculating drencher can spread more decay pathogens than the single-pass application. But, the study shows differences depending on the fungicide used, Amiri said.
“If the fungicide is effective, we expect that the recirculating drencher should not be spreading spores, but if they have resistant spores, it might be spreading them,” he said.
In 2021 trials, using fludioxonil, they did not see any spores spread. But in 2022, with pyrimethanil, they did.
“What was striking was that blue mold significantly reduced in the fruit treated with the single-pass applicator,” Amiri said. He saw similar findings for mucor rot, the other postharvest pathogen that can spread through water.
Matson’s approach also uses a lot less water overall.
“It’s more like a spray than a drencher,” Amiri said.

The fruit in the trial did not receive a preharvest fungicide application, which Amiri said is a better timing to protect against gray mold, so he recommends both.
When Amiri analyzed decay rates, he found equal or better efficacy from the single-pass approach.
There’s real value in reducing that decay incidence, and it helps to manage the risk of fungicide resistance, Matson and Miles both said. And the approach could be a benefit to organic orchards, Miles and Amiri both added, now that there are few registered postharvest materials available.
“What’s the percentage of organic product that goes to waste because of decay? One way to change your climate footprint is to get more of the food you put inputs into producing into the hands of customers,” Miles said. “For an organic Honeycrisp grower, it would pay for itself all day long.”
Harvest logistics
Matson deployed old spray tanks to hold the postharvest fungicides and bought simple remotes and stopwatches for tractor drivers to control the application. He found the right nozzles to deliver sufficient coverage as the bins pass under the spray and back out, with a 30 second pause in between, which was the key to getting sufficient residue, he said. The platforms — a welded steel catchment tray that the tractors can drive over — are portable.
Well, “pseudo-portable,” Matson said. “You have to level the dirt and gravel out underneath it, so you want it to be out there a couple of weeks.”
A local welding company fabricates the platforms.
The downside to adopting the single-pass application is that it changes the harvest logistics to get the bins through the drencher before they are stacked to await loading, Matson said. Once harvest gets busy, they might have more fruit than one system can handle, so they may have to move two drenchers to the same area.
The other challenge: getting sufficient fresh water to the orchard where the system is set up.
“Let’s say you are doing 1,000 bins a day, and each bin gets 3 gallons, so you need to be cycling through 3,000 gallons,” he said.
Wastewater, on the other hand, does not pose a problem. They pump out the catchment every 200 bins or so and use the water to spray for dust abatement. *
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