As Washington growers have ramped up production of organic apples, the volume of apples going into storage has also increased, and with it, the need to for longer storage. With few postharvest tools available for organic fruit, more research is needed to find ways to improve organic fruit storage, says a Stemilt Growers representative.
Jake Gutzwiler of Wenatchee, Washington’s Stemilt Growers, Inc., has studied Stemilt packout data for the last five years of both conventional and organic apples. Stemilt has had a large volume of organic Golden Delicious apples for many years, he noted, but also has experience storing other organic varieties.
Although there is a steady decline in packouts as fruit age in both conventional and organic categories, there is a much more precipitous decline in organic packouts after late winter-early spring, he said. “From February on, in organic Golden Delicious, we see a rapid decline. The same thing happens in organic Red Delicious.”
Postharvest problems include decay and bull’s-eye rot on Golden Delicious, scald on Granny Smith, and decay towards the end of the storage season on Red Delicious. With Reds, once decay starts popping up, fruit need to be packed and shipped quickly, he said.
“Why can’t we hold organic apples like we can hold conventional apples?” he asked.
Although organic and conventional apples are physiologically the same and picked at the same maturity levels, there are few tools in the organic grower’s arsenal of preharvest fungicides to apply, he said during the Washington State Horticultural Association’s annual meeting in Wenatchee.
At the warehouse level, the only tools available to stave off scald and decay include controlled atmosphere, dynamic controlled atmosphere (ultra-low oxygen levels), and ozone, Gutzwiler said.
“It’s like bringing a knife to a gun fight,” he said, referring to the organic postharvest tools available. “There are not a lot of options for organics.”
Successes and failures
Stemilt has had success for many years in postponing scald development and reducing firmness decline in Granny Smith and Red Delicious apples by implementing dynamic controlled atmosphere, known as DCA, Gutzwiler said. The ultra-low oxygen storage technique brings fruit down to oxygen levels lower than typical storage programs by using sensors to monitor their fruits’ respiration.
“But in order to do this, we’re taking fruit to the brink of death, slowing down respiration and metabolism a little more than standard controlled atmosphere,” he said. “How low can we go? What are the limits?”
Two years ago, Stemilt’s organic production increased dramatically. The successful DCA technique was applied to other varieties. But one of Stemilt’s flagship organic varieties had low-oxygen injury from the DCA, he said, causing the company to question how much benefit they really are getting for the improvement in firmness and decay.
They are now wondering if the risk is worth the benefit of stretching out storage just a little longer.
Back to basics
Gutzwiler encourages organic growers and warehouses to go back to the basics of doing everything possible in the orchard to deliver clean fruit to the warehouse.
For growers, that means implementing sound cultural practices and picking fruit at the right time. For warehouses, it means putting fruit in the proper storage rooms, watching the maturity indices, and storing fruit in optimum conditions.
He believes that researchers have yet to determine the optimum temperature, oxygen, and carbon dioxide levels, and timing for each variety. He advocates for more research into the storage of organic fruit, at both the individual warehouse level and collectively as an industry.