Honeycrisp is a unique apple and will present new challenges for fruit packers as commercial production increases.The variety is susceptible to a number of disorders, including soft scald and soggy breakdown, as well as bitter pit.
It can also develop off flavors, Dr. Chris Watkins, horticulturist at Cornell University, Geneva, New York, reported at an Apple Fruit Quality seminar organized by Washington State University Extension in Yakima this summer.
Honeycrisp is a popular apple, and brings high returns for growers. But as volume increases and the variety is stored longer, storage issues will need to be addressed. New York doesn’t store the apple in controlled-atmosphere storage, Watkins said.
“Whenever we’ve tried Honeycrisp in CA in Michigan and Ontario, we have a disaster. It doesn’t respond well to standard CA conditions. Nova Scotia has used CA apparently successfully, but I’m not sure why that should be.
“It’s not been an urgent issue for us because there aren’t enough apples to supply the demand,” he added. “But it’s going to be a major issue in Washington very soon with the volumes that are coming on stream.”
Soft scald
The storage disorder soft scald (deep scald) is more prevalent on late-harvested fruit, though there are wide variations from orchard to orchard that researchers don’t yet understand. Symptoms of soft scald are sharply defined brown lesions on the skin of the apple that can extend into the flesh.
Soggy breakdown is an internal disorder, which can result in a complete ring of soft, brown spongy tissue. It is often, but not always, associated with soft scald, and can be a nasty surprise for the unsuspecting consumer who bites into an affected apple, Watkins said.
Another problem related to fruit maturity is stem-end cracking, which is worse with later harvests and can provide opportunities for decay to develop in storage. Alcoholic off flavors in the fruit are also related to maturity. To reduce the potential for these disorders, the fruit should be picked before it is overmature, Watkins said, but there’s a danger that growers will harvest the variety too early, and destroy the reputation of the apple for good flavor.
Maturity
Most of the usual maturity indices for apples do not apply to Honeycrisp. In most apple varieties, once the apple begins to produce internal ethylene, the level rises autocatalytically and they produce more and more ethylene. In contrast, Honeycrisp has a very limited ability to produce ethylene, Watkins said, and the internal ethylene concentration can go down during the ripening period.
For that reason, the ethylene concentration is not a good indicator of maturity in Honeycrisp. The variety does not respond well to preharvest ethylene inhibitors Retain (aminoethoxyvinylglycine) or Ethrel (ethephon). Neither is starch a good indicator of maturity because usually when Honeycrisp harvest begins, starch hydrolysis is well advanced.
In some cases, the fruit can be in optimal condition when there is no starch left in the apple, Watkins said. Honeycrisp is also unusual in that the soluble solids levels do not increase over the harvest period. “People hang on to Honeycrisp to get higher soluble solids, but it doesn’t work as a strategy,” he warned.
Although firmness declines during the harvest period, it does so at a much slower rate than other varieties do, so pressure is not a useful maturity indicator, either. And, a pressure tester does not really measure the crisp texture and unique characteristics of the apple, Watkins said. Lacking the usual maturity indicators, growers have to spot-pick Honeycrisp when the fruit looks like it’s ready to be harvested, he said.
However, a proportion of the fruit will not develop sufficient color. Watkins said there’s a two-week harvest window for the best long-term quality, even through there’s a four-week period when the fruit will look very similar. A factor that should be considered is the change in background color from green to cream yellow.
Storage temperature
At the usual storage temperatures, Honeycrisp has a relatively short shipping window, Watkins said. When the fruit is held at 32°F, it might start to develop an undesirable alcohol flavor after six weeks. Soft scald symptoms will become visible in 10 to 12 weeks.
But there are storages in Washington that are storing Honeycrisp at 32°F and have never had a problem with scald, Watkins noted. “You never know in this business whether that’s just lucky.” Researchers in New York have found that incidence of soft scald and soggy breakdown is lower when the storage temperature is raised to 38°F.
Though with other varieties there would be a concern about loss of firmness in the apples, with Honeycrisp that is not an issue because of its good storability. In tests where the storage temperature was raised to 41°, there was even less soft scald, but there was a tremendous amount of decay. Watkins and his colleagues found that holding the fruit at 50°F for a week before cold storage reduced soft scald even further.
Decay
They found that treatment with MCP (1-methylcyclopropene) had only a small effect on soft scald, and DPA had very little effect. Watkins said he strongly recommends that packers don’t treat Honeycrisp with DPA because of the risk of inoculating the fruit with decay organisms.
Honeycrisp is prone to stem punctures, which provide entry points for disease organisms. The apples have rigid, thick stems that can puncture other fruit. Fruit can also be punctured in the stem bowl area by the sharp buds on the spurs.
Bitter pit
While scald and soggy breakdown can be reduced markedly with the delayed storage treatment, there is a risk of increased bitter pit, to which the variety is particularly susceptible. “If the fruit is susceptible to bitter pit, it’s goodbye soft scald, hello bitter pit,” Watkins warned.
“You have to do a topnotch job in the orchard to reduce bitter pit before the fruit is harvested.” He recommends applying 6 to 14 pounds of calcium per season, in six or more foliar applications and stressed that it’s also important to keep the crop load in balance.
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