A summary of this article appeared in the August, 2010, issue of the Good Fruit Grower.
Honeycrisp with CA-storage damage.
Randy Beaudry, Michigan State University
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,” says 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. Jenifer DeEll in Ontario 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.
Here are some of the findings from his report:
Luckily for growers in Washington, 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 to treatments with SmartFresh (1-MCP), but in Minnesota, New York, and Nova Scotia, it is not recommended.
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, ranging from 34° to as high as 41°.
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°, compared to 37-41° in Nova Scotia.
The recommended storage conditions and protocols are summarized in the table Beaudry compiled.
Here’s some of what the respondents had to say about Honeycrisp storage in their area:
Dr. Gene Kupferman, Washington State University, and Dr. Jim Mattheis, USDA Agricultural Research Service, responded to the survey.
Honeycrisp is likely the most challenging apple variety grown commercially in Washington State. Research undertaken in recent years by scientists at the Tree Fruit Research Laboratory in Wenatchee confirms the challenges facing the industry in judging maturity and storage.
We recommend that storage operators set up their own trials on maturity, drenching, pre-storage conditioning, and storage to gain firsthand experience. It is critical to be aware that this is a very chilling-sensitive apple. The disorders that can develop from rapid cooling or excessively cold storage temperatures include soft scald and soggy breakdown.
Judging maturity on Honeycrisp is not simple. 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.
Most commercial experience has been to use the change in ground color from green to white to time the harvest, providing commercial red color has been reached. Typically, when maturity is judged using background color little starch remains in the fruit, thus the life of the fruit in long-term storage is shortened. Research from scientists in the eastern United States has shown that the risk of soft scald increases in early-harvested fruit even when caution is taken to avoid chilling after harvest.
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 shown to be effective in reducing storage disorders whether fruit are to be placed in controlled atmosphere or air storage.
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.
Honeycrisp has a high potential for decay. Therefore, the postharvest application of a fungicide drench or preharvest fungicide spray should be considered. In research trials, the application of SmartFresh has shown to reduce acidity loss, greasiness, and internal radial browning. SmartFresh has not been identified as affecting the risk of soft scald or soggy breakdown.
Research with Washington-grown Honeycrisp has shown that when the fruit have been stored in the upper 30s, over time they become greasy, the skin color changes, and acidity is lost. Limited storage trials at 35 to 36° F have given a better balance of quality and reduction of storage disorders. Temperatures in the lower 30s have resulted in an increase of storage disorders.
This apple has not easily lost firmness after harvest, but there has been little work on the effect of storage on the retention of the special characteristics of aroma, flavor and texture.
CA storage at 35° F has given good results with oxygen levels at 2% and carbon dioxide levels at 1%.
Researchers in the eastern United States report that the use of wax on Honeycrisp could lead to severe internal breakdown in as little as 5 to 10 days in storage.
Beaudry said the most important harvest maturity indices include starch index (4-6), red coloration, and change in background color from green to yellow. Most growers pick their blocks three or four times.
Typical preconditioning temperatures and durations are 50° F. for 5 to 7 days before cold storage. CA storage is still being evaluated.
SmartFresh (1-MCP) application is recommended, especially for long-term (5-7 months) air storage. DPA application is not advised as a dip to avoid spread of fungal spores. DPA provides only a marginal benefit in the prevention of soft scald. Impact on internal CO2 injury is being evaluated. 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.
Air storage at 38° F can hold Honeycrisp for 3 to 4 months. CO2 levels should remain below 1% during loading. In experiments 3% oxygen yielded less CA injury than 1.5%. Early research results on carbon dioxide levels suggest maintaining CO2 levels below 1% for at least the first 30 days of storage.
Although CA storage is not currently advised, some success has been achieved experimentally and at some storage facilities in Michigan. Marked differences in susceptibility to CA injury were detected between growers and growing regions. Temperatures in CA will likely have to be greater than 36° F due to sensitivity to chilling injury.
Dr. Cindy Tong, University of Minnesota, said the most important harvest maturity indicator is change in background color from green to yellow. Growers typically pick each block 2 or 3 times.
Typical preconditioning temperatures and durations for air storage are 55° F for 5-7 days, with storage at 34-36°F, usually done by the end of January. CA storage is not recommended, but some success has been achieved at some commercial storage facilities.
A web site on Honeycrisp Apple research results has been developed. The address is: http://smfarm.cfans.umn.edu/honeycrisp.htm
Dr. Christopher Watkins, Cornell University, responded with these thoughts, among others.
Most important harvest maturity indices are color and flavor. Growers pick 3-6 times.
CA storage is not recommended, though several folk have had mixed success.
I discourage postharvest drenches of any sort because of decay risk. The apple is
easily damaged and even with fungicides it’s not worth the risk.
Dr. Robert Prange, Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre, Kentville, replied.
Clip fruit stems to control decay. When considering harvest, the change of fruit starch to sugar is a reliable initial indicator of Honeycrisp readiness. The change in background color from green to cream is a good visual indicator of when to begin harvest. Growers repeat spot-pick for size and color.
Delaying cooling and preconditioning is essential to control disorders. During delay-cooling treatment, O2 and CO2 should be monitored to avoid the occurrence of unsafe levels for both human activity and the fruit.
SmartFresh application is not recommended and may cause CO2-like disorders even in air storage. Drenches of any kind are not recommended.
Retention of constant firmness throughout the refrigerated air storage period may cause one to question the necessity for CA for Honeycrisp apples. Controlled atmosphere storage reduces the incidences of fruit decay and greasiness and maintains juiciness and flavor when compared with cold stored apples. Storage operators must ensure that the desired storage temperature of the fruit is obtained prior to applying CA conditions to the sealed storage room.
For CA storage of 6 to 12 months, we recommend oxygen levels of 0.5%-0.8%, up to 2%. We have observed experimental evidence of CO2-related injury. CO2 should initially be scrubbed to less than 1% for 3 to 4 weeks prior to allowing it to accumulate up to, but not exceeding 1%.
Our research has demonstrated that Honeycrisp fruit harvested during the optimum harvest window and delayed cool-treated results in superior fruit quality after storage. Honeycrisp fruit do not have ultra low oxygen sensitivity and fruit have been stored experimentally in Dynamic Controlled Atmosphere (DCA) at 0.7% O2 without injury for 9 months. Waxing should be done with caution as excessively thick wax can cause total deterioration of the fruit within 2-4 days.
Dr. Jennifer DeEll, Ontario Ministry of Agriculture, Food and Rural Affairs, Simcoe, Ontario, is one of the leading figures in the research. She added this thought, among others.
1-MCP application can reduce greasiness but has little effect on firmness or disorders. Avoid drenching of any kind, and use lots of calcium sprays in the orchard.