After researching this temperamental apple variety for several years, Dr. Randy Beaudry has developed a set of guidelines for harvesting and storing Honeycrisp apples.
Beaudry is the post-harvest physiologist at Michigan State University. Pressure has been building, slowly, for him and other storage experts to figure out how to store this much-demanded variety longer to accommodate an increase in production and a lengthening marketing season.
Beaudry’s protocols, developed with his Ph.D. students Carolina Contreras and Diep Tran, now extend storage up to nine months, maybe a tad longer. The protocols vary depending on whether storage will be in regular air storage or modified atmosphere, and whether or not the apples will be treated with diphenylamine (DPA) or 1-MCP (1-methylcyclopropene or SmartFresh).
Honeycrisp has shown itself to be very sensitive to carbon dioxide injury and chilling injury, and apple quality after storage very much depends on the maturity of the apples at harvest. The storage protocols start in the orchard.
And that’s where Beaudry spoke to growers about it—standing in the sun in Ridgeview Orchards, operated by Joe, Al, Dan, and Ryan Dietrich, in Conklin, Michigan, during the Michigan Pomesters fourth annual RidgeFest fruit grower tour this summer.
Each of the storage protocols starts with the same trio of admonitions:
—First, don’t try to store apples that are not properly mature. “Harvest at optimal maturity,” Beaudry said.
That means using the Cornell Starch Chart and harvesting before apples reach 60 percent starch clearing, or read less than 6 on the starch index chart. Apple background color should not have entirely changed from green to yellow.
—Second, Honeycrisp apples need to be preconditioned before they are moved into storage. There is still some variation in the practice, between “mild preconditioning” and “intense preconditioning,” but each involves holding apples at warmer temperatures for a few days before moving them into colder air or CA storage.
The mild form is to hold the apples from five to seven days at a temperature of 50° to 68°F to suppress chilling injury for either air or controlled atmosphere storage conditions and CA injury in controlled atmosphere storage.
During that period, the fruit should be stored in conditions—vented if necessary—where carbon dioxide levels can’t build above 1 percent. “This is especially important for fruit from young trees,” Beaudry said.
The intense form of preconditioning is to hold the apples at a higher temperature, 70° to 77°F, for a shorter time, three to five days. “This more intense form of conditioning will help protect the fruit from injury caused by low oxygen and high carbon dioxide levels found in CA storage,” Beaudry said.
—The third essential element is storage temperature. For all storage conditions—air or CA—and durations, storage temperature should be held preferably at 38°F and certainly not lower than 36°F.
Packers can use either 1-MCP or DPA, or both together.
In air storage, Honeycrisp can be held up to four months with no chemical treatments. If 1-MCP is used, it should be applied at 1 part per million for 24 hours at the time of preconditioning. The 1-MCP will extend the storage life to six to seven months.
Drenching with DPA is not recommended before short-term air storage.
For CA storage without treatment with either DPA or 1-MCP, the recommended procedure is, after preconditioning, to store at 36°F to 38°F for a least a month with the carbon dioxide level below 1 percent and oxygen level between 1.5 and 3 percent. Then, the carbon dioxide and oxygen levels can be raised to 3 percent each and the apples stored for an additional six to eight months.
If the intense preconditioning program is used, the month of storage at lower carbon dioxide may not be necessary. Beaudry is still studying the intense program.
If 1-MCP is used alone, the treatment protocol for CA storage is the same as for air storage, but the CA conditions will extend the storage life to about nine months. “Fruit can be held longer if initial apple maturity was less,” Beaudry added.
He recommends use of a DPA drench at 250 to 1,000 ppm (if your intended market allows this use) before preconditioning on apples that go into CA storage.
“DPA is very effective at suppressing CA injury in Honeycrisp and would certainly be able to substitute for a preconditioning treatment in terms of controlling CA injury,” he said. “However, since DPA has only a slight suppressive effect on chilling injury, a minimal prestorage conditioning program (five to seven days at 50°F) is still advisable in air or CA storage.”
No matter how the Honeycrisp will be stored, a critical step is having a good preharvest decay control program, Beaudry said.
Honeycrisp apples are prone to storage rots as well as injury from carbon dioxide and chilling. •