MSU Extension Apples

Honeycrisp apple fruit are difficult to store due to a number of postharvest issues. One of the most important problems is the extremely high sensitivity to chilling (Fig. 1). Pre-storage conditioning (five to seven days at 50 - 60 Fahrenheit) provides good protection, but the fruit still need to be stored at temperatures a few degrees above freezing. Our recommended storage temperature is 36 - 38 F; lower temperatures may be successful sometimes if the fruit are conditioned, but we have seen problems following storage of pre-conditioned fruit at 32 F. Prestorage conditioning can enhance the development of bitter pit, so our recommendation is to selectively store fruit with low potential for bitter pit development where possible. Honeycrisp are also sensitive to injury by CO₂ in storage (Fig. 2). The injury due to CO₂ is slightly higher for less mature fruit and it is also dependent upon the O₂ level in the storage in such a way that lower O₂ levels increase injury. We recommend some form of protection from CO₂ injury, and we have previously had very good success for several years with an intense conditioning period of five to seven days at 68 F. A shorter conditioning period (three days) at higher temperatures (75 - 80 F) may be similarly effective. Unfortunately, this form of intensive conditioning can advance ripening and can slightly shorten storability. Treatment with diphenylamine (DPA) as a drench or thermofog is very effective at suppressing CO₂ injury in Honeycrisp and would certainly be able to substitute for a preconditioning treatment in terms of controlling CO₂ injury. DPA has no meaningful suppressive effect on chilling injury. Another alternative to CA storage is the use of 1-MCP to suppress ripening. Results so far have been quite favorable, but there may be a slight enhancement of sensitivity to CO₂ injury. Also, 1-MCP treatment has been known to exacerbate a disorder known as leather blotch (Fig. 3), which is orchard-specific, and little is known about causes of this injury. We strongly recommend monitoring CO₂ levels during room loading and the initial cooling period, venting the room if necessary. That being said, high O₂ levels (e.g., air with 21% O₂) suppress CO₂ injury. The following are our recipes for storage of Honeycrisp with some estimates of storability. These recommendations are drawn from work by MSU, Cornell, Washington State, and Ontario researchers. More information on the harvest and maturity of Honeycrisp and other apple fruit can be found at MSU Extension.

Pre-storage

Color management

Honeycrisp, like most, if not all apple cultivars, typically store better if they are harvested early in the maturation, rather than later. To harvest Honeycrisp on the early side, use available tools (reflective ground covers, pruning for maximizing light penetration, use early coloring cultivars, avoid early ripening cultivars). 

Bitter pit management

Manage crop load and minimize biennial bearing to even out production and reduce the risk of bitter pit. Provide adequate calcium using five to eight sprays beginning shortly after fruit set. Avoid bitter pit promoting rootstocks and orchard sites. Use historical records to identify risky sites and avoid them for long-term storage.

Harvest management

Use of early coloring cultivars (not early ripening cultivars like Premier and others) and growth regulators is encouraged. Use lower rates of ReTain (repeated applications can be OK) or Harvista - with or without NAA to control fruit drop. Better color might be obtained from Harvista-treated blocks since the inhibitory treatment is later in development and can interfere with red coloration less than ReTain.

Air storage

Air storage (no 1-MCP)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees).
3. Store at 36 - 38 F for three to four months, slightly longer if initial maturity was less.

Air storage (with 1-MCP)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Treat with 1-MCP (1 ppm, 24 hr) during preconditioning if possible. Repeat applications of 1-MCP are not helpful if the interval is 1.5 months of greater.
3. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees).
4. Store at 36 - 38 F for up to five months, slightly longer if initial maturity was less.

CA Storage

CA storage (no DPA, no 1-MCP) 

OPTION 1 (mild preconditioning)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees).
3. Store at 36 - 38 F for at least a month with CO₂ levels ~ 0.5 to 1% and O₂ between 1.5 and 3%. Then:
   • Standard CA: Store at 36 - 38 F for an additional ~ five to six months (~ six to seven months total) with CO₂ level 3% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 – 38 F for ~six to seven months (~ seven to eight months total) with CO₂ level of 1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.

OPTION 2 (intense preconditioning to help control CO₂ injury)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Precondition for three to five days at 70 F to suppress chilling and CA injuries (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees). Intense preconditioning will shorten storability somewhat and can enhance bitter pit development. Then:
   • Standard CA: Store at 36 - 38 F for ~ six months with CO₂ level of <1% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 – 38 F for ~ six to seven months with CO₂ level of 1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.

CA storage (no DPA, with 1-MCP) 

OPTION 1 (mild preconditioning)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Treat with 1-MCP (1 ppm, 24 hr - at same time as preconditioning).
3. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees).
4. Store at 36 - 38 F for up to a month with CO₂ levels below 1% and O₂ between 1.5 and 3%. Then:
   • Standard CA: Store at 36 - 38 F for ~ six to seven months (~ seven to eight months total) with CO₂ level less than 1%% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 - 38 F for ~ seven to eight months (~ eight to nine months total) with CO₂ level of less than 1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.

OPTION 2 (intense preconditioning)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Treat with 1-MCP (1 ppm, 24 hr - at same time as preconditioning).
3. Condition for three to five days at 70 F to suppress chilling and CA injuries (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees). Intense preconditioning will shorten storability somewhat and can enhance bitter pit development. Then:
   • Standard CA: Store at 36 - 38 F for ~ six to seven months with CO₂ level less than 1%% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 - 38 F for ~ seven to eight months with CO₂ level of <1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.

CA storage (with DPA, no 1-MCP)

1. Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed 1% - this is especially important for fruit from young trees). Then:
   • Standard CA: Store at 36 - 38 F for ~ six to seven months with CO₂ level less than 1% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 - 38 F for ~ seven to eight months with CO₂ level of ~1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.

CA storage (with DPA, with 1-MCP)

1.  Harvest at optimal maturity - prior to 60% starch clearing (Starch Index less than 6 on Cornell Starch Chart) and ground color change from green to yellow.
2. Treat with 1-MCP (1 ppm, 24 hr - at same time as preconditioning).
3. Precondition for five to seven days at 50 F to suppress chilling injury (make sure CO₂ levels do not exceed  1% - this is especially important for fruit from young trees).
   • Standard CA: Store at 36 - 38 F for ~ eight months with CO₂ level of 3% and O₂ between 1.5 and 3%. Fruit can be held longer if initial maturity was less.
   • Low O₂ CA: Store at 36 - 38F for ~ nine to ten months with CO₂ level of ~1% and O₂ level of 0.5 to 1% (use DCA technology if available). Fruit can be held longer if initial maturity was less.