A new CA control system supplied by Storage Control Systems, Sparta, Michigan, was installed at Michigan State University in 2008. Employee Dan Boozer is pictured. The new lab contains individual cabinets in which small lots of fruit can be held under tightly controlled conditions.
As more and more Honeycrisp apples come to market each year, growers need to store more of them and sell them over a longer season. Increasingly, they’ll have to come to grips with this fact: Honeycrisp do not store well.
For several years, postharvest physiologists have anticipated this growing need and have tried to develop a storage protocol for this finicky apple.
“Although the variety was bred as part of a breeding program to develop winter-hardy cultivars, the fruit have proven to be quite sensitive to low temperatures encountered in storage,” said Michigan State University postharvest physiologist Randy Beaudry. “Low temperature injury symptoms include soggy breakdown and soft scald. There appears to be a marked sensitivity to injury from low oxygen and elevated carbon dioxide.” That injury appears as internal browning.
“To date, no satisfactory method for the controlled atmosphere storage of Honeycrisp apple has been determined here in Michigan. Honeycrisp is the most profitable apple on a per-fruit basis grown in our state, and the number of bearing acres is increasing dramatically each year. The increased production will require storage for longer durations than previously needed in order to market the crop before value is lost due to the deterioration of the fruit. If we do not develop a means to store this fruit satisfactorily, our growers and storage operators will suffer excessive storage losses and be at a marked disadvantage in the marketplace.”
To meet the needs of Michigan growers, Beaudry conducts his own research and has collaborated with postharvest physiologists in other regions to see how they handle Honeycrisp. The protocol is somewhat different depending on where the apple is grown.
Moreover, the protocols are evolving. Last year, Beaudry successfully used DPA to reduce CA storage injury. Jennifer DeEll in Ontario, Canada, was able to suppress storage disorders with 1-MCP. But these results are not yet ready to incorporate into recommendations, Beaudry said.
Last year, Beaudry surveyed his fellow apple storage researchers across the continent and compiled current region-by-region storage recommendations for Honeycrisp, recognizing that these recommendations may change as we learn more.
Luckily for growers in Washington State, where growing apples for a long marketing period is very important, Honeycrisp grown there can be held in controlled atmosphere storage. In Minnesota, where this apple was born, CA storage is not recommended. And it is also not recommended in Michigan, New York, and Ontario, where the variety is very desirable and is widely planted. Growers in Nova Scotia, who, like Washington growers, grow for distant markets, also can store the apple in CA storage—the only two areas where it is recommended.
In three of the states and provinces—Michigan, Ontario, and Washington—Honeycrisp responds well to treatments with SmartFresh (1-MCP), but in Minnesota, New York, and Nova Scotia, SmartFresh is not recommended for use with Honeycrisp.
In every region, a preconditioning period is recommended before putting the apples into either air or CA storage. Each state or province has its own recommendation, but generally it is to hold the apples at 50°F or higher for from five to seven days before putting them into storage.
Recommended air storage conditions vary somewhat by region as, ranging from as low as 34°F to as high as 41°F.
CA storage conditions recommended in Nova Scotia and Washington are quite similar—2 percent oxygen, 1 percent carbon dioxide—but temperature recommended is lower for Washington, 35°F, compared to 37° to 41°F in Nova Scotia.
The recommended storage conditions and protocols are summarized in the table “Storage recommendations for Honeycrisp” on page 17.
Dr. Gene Kupferman, Washington State University postharvest specialist, and Dr. Jim Mattheis with the U.S. Department of Agriculture’s Agricultural Research Service, said that Honeycrisp is likely the most challenging apple variety grown commercially in Washington State.
“We recommend that storage operators set up their own trials on maturity, drenching, prestorage conditioning, and storage to gain firsthand experience,” they said. “It is critical to be aware that this is a very chilling-sensitive apple.”
Judging maturity on Honeycrisp is not simple, they said. Fruit firmness does not change during the maturation stage, and, in most locations, when starch is only moderately cleared the fruit are not commercially acceptable.
Research in Washington and New York has shown success when Honeycrisp is held at or about 50°F for seven days prior to being placed in cold storage. The delay in temperature reduction has been effective in reducing storage disorders.
However, when bitter pit-susceptible fruit are held at these warm temperatures, this disorder can become a big problem. Minimization of bitter pit risk in the orchard is important. There has been little success in increasing calcium in apples through the use of postharvest calcium drenches.
The most important harvest maturity indices include starch index (4-6), red coloration, and change in background color from green to yellow, Beaudry reports. Most growers pick their blocks three or four times.
Typical preconditioning temperatures and durations are 50°F for five to seven days before cold storage. “We are still evaluating CA storage,” he said.
SmartFresh (1-MCP) application is recommended, especially for long-term (5-7 months) air storage. DPA application is not advised as a dip because of the risk of spreading fungal spores. DPA provides only a marginal benefit in the prevention of soft scald. Thermofogging needs to be investigated. Calcium dips are not advised for same reason as for DPA, unless growers have not been spraying calcium in orchard preharvest.
Although CA storage is not currently advised, some success has been achieved experimentally and at some storage facilities in Michigan, Beaudry said.
Dr. Cindy Tong, University of Minnesota, noted that a Web site on Honeycrisp research results has been developed. The address is: http://smfarm.cfans.umn.edu/ Honeycrisp.htm.
Dr. Jennifer DeEll, Ontario Ministry of Agriculture, Food and Rural Affairs, Simcoe, Ontario, is one of the leading figures in the research. 1-MCP applications can reduce greasiness but have little effect on firmness or disorders, she has found. Avoid drenching of any kind, and use lots of calcium sprays in the orchard.