—by Ross Courtney

Postharvest pear practices were on the menu at the Washington State Tree Fruit Association Annual Meeting in December in Yakima, with three of the six speaking slots during the pear session dedicated to decay prevention in stored fruit.
“We’re a little heavy on the postharvest right now, because I believe that it is one of the real keys to success,” said Ed Ing of Mount Adams Fruit, the session moderator. “It’s difficult to keep costs down in the warehouse. So, these speakers are thinking of novel ways to make it all more possible.”
Because postharvest success starts with field practices, Tim Pitz, orchard manager for Mount Adams in White Salmon, shared how to ward off fungal pathogens before fruit reaches storage.
The White Salmon pear orchard sees about 40 inches of rain per year, he said, a lot compared to the more arid Yakima Valley and Wenatchee Valley, Washington’s other large pear production regions.
Much of his advice was common sense but worth repeating, he said.
“Decays come from all kinds of places, and we get to deal with them all,” he said.
Handle fruit with care, he said. Bumps and bruises cause wounds that give decay an opening. Same goes for pest injuries, he said as he showed photos of fungal infections that started with leafroller and brown marmorated stink bug feeding. Sunburn also causes injury that gives decay a foothold.
To avoid resistance, speak to chemical field reps about fungicides with different modes of action, noted by FRAC group labels, he said. Also talk with warehouse managers about the FRAC groups they plan to use, so you don’t use the same.
Organic decay management requires a lot of trial and error. Pitz recommends setting up trials to test biofungicides, because efficacy varies depending on location.
Timing is important, he said. Alternaria rot and gray mold infect fruit at full bloom but won’t show symptoms until storage, according to Washington State University research. Pitz’s crews apply a “tweener” fungicide between the traditional timings of pink and petal fall, especially in wet and cool years, to keep within a 14-day application interval, he said. The time of day matters, too. In White Salmon, trees sometimes drip dew until 10 a.m. Applying in those conditions could cause russeting.
To boost coverage, calibrate sprayers for the canopy size and use paper strips to test the settings. Managing vigor is also important, he said. During nondormant times, Mount Adams hedges and tops trees, and crews remove central branches to improve sun exposure and spray coverage. Plant growth regulators also help, he said.
Don’t rush bins into the orchard, where they will collect moisture and pathogens, he said. Wait until just ahead of picking, if possible. If rain is in the forecast, pick Boscs before Anjous. Boscs seem more susceptible to bull’s-eye rot, in his experience.
In the warehouse
David Rudell, a research plant physiologist with the U.S. Department of Agriculture in Wenatchee, gave the crowd a few best practices for controlling superficial scald on Anjou pears once they hit the warehouse. Superficial scald is a disorder caused by chilling injury that leads to irregular, diffuse browning on the surface of apples and pears.
First off, know how it started, Rudell said. Most likely the damage happened within the first couple of months of cold storage (if the fruit was not protected by controlled atmosphere, 1-methylcyclopropene or ethoxyquin) even if symptoms don’t develop until later. Research indicates that risks are reduced by loading CA rooms and establishing settings within seven days of putting fruit in cold storage.
The oxygen level in those CA rooms matters, Rudell said. In his research, funded by the Fresh and Processed Pear Committee, he found that bringing oxygen down to 0.5 percent at 31 degrees Fahrenheit gave the best control of scald with less of an increase in the risk of internal disorders, such as pithy brown core, compared with higher oxygen levels or storage temperatures.
The ethylene blocker 1-MCP also prevents scald, but it can prevent pears from ripening at all.
“It’s a trade-off,” Rudell said.
Currently, he is researching how to find the right balance of 1-MCP rates, oxygen and carbon dioxide levels, storage duration and temperature to end up with fruit that ripens for the customer with no scald or internal browning.
Meanwhile, ethoxyquin, an antioxidant used as a food preservative, can be applied to pears as a drench or with an impregnated wrap to prevent scald. But its future availability for use in some export markets is uncertain due to anticipated revocation of its Codex tolerance.
David Felicetti of AgroFresh, a postharvest product and technology company, stressed the importance of sanitation and rotating fungicides in the warehouse.
He suggested cleaning and sanitizing bins before putting them in the fields, doing the same to storage rooms as soon as they are empty and adding sanitizer to packing line flume water. Those moves make food safety sense but also could help reduce incidence of decay, he said.
He told growers that resistance to fungicides has been increasing in the past 20 years. In one 2019 study in Washington, Achour Amiri of WSU found a resistance frequency of nearly 25 percent with thiabendazole, one of the industry’s stalwart fungicides since the 1960s. Some pathogens also have been showing resistance to pyrimethanil and some reduced sensitivity to fludioxonil, released in 2004.
To reduce the risk, Felicetti reminds growers to rotate FRAC groups in the warehouse. Use pyrimethanil one year, then switch to a mixture of fludioxonil and thiabendazole. Fludioxonil controls for many species of bull’s-eye rot but not all, so adding thiabendazole broadens the spectrum.
However, this rotation will not control mucor rot, he said.
For that he recommends natamycin, an antimicrobial peptide commonly used as a food preservative. Since the acquisition of Pace International last year, AgroFresh now sells BioSpectra, which uses natamycin as the active ingredient. It’s effective against mucor rot and labeled for organic use, he said. It also is effective on other rots and can be used if resistance is a concern, he said.
He echoed Pitz’ suggestion about communication between warehouse and growers to avoid repeating fungicides.
“You should be talking to your growers, or you should be working with your orchard to make sure that they’re not applying … fungicides that may contradict your plan for the postharvest application,” he said. •
Leave A Comment