Production and pest update brought to you by the OMAFRA Apple Team: 

Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

Apple harvest has kicked off across the province with Sunrise, Paulared, Gingergold and Zestar being picked. Premier Honeycrisp harvest will begin shortly, with discussions of Gala harvest beginning in early region before the end of the month.

Continue to protect the maturing fruit from late-season insects (such as apple maggot and codling moth) and disease (such as scab, black rot and bitter rot). Pest management will be especially important during wet weather like what is predicted in the coming days. Be mindful of preharvest intervals for all pest control products applied.

Predicted Harvest Timings

Generally speaking, apples in Ontario seem to be roughly 14 days ahead in the early regions. The predictions proposed by Michigan State University seem to demonstrate that trend as well. For more variety specific predicted timings based on regions in Michigan, please check the links below.

The following information was provided by Jennifer DeEll, OMAFA Horticulture Fresh Market Quality Specialist. Stay tuned for the next issue of ONCore Newsletter coming soon which dives deeper into preharvest considerations for this year’s crop.

For successful long-term storage, apples must be harvested when they are physiologically mature but not fully ripe. Each cultivar must be harvested at the proper maturity to achieve maximum storage life and marketing season, while minimizing postharvest losses. 

Methods to Determine Harvest Dates

Days After Full Bloom

Days after full bloom is overall somewhat constant but can vary in a year with weather extremes. Therefore, days after full bloom should be used as a general reference to indicate the approximate date when apples might reach harvest maturity, which is then confirmed using tests such as internal ethylene concentration (IEC), starch-iodine staining, flesh firmness, and soluble solids content (sugars). 

Internal Ethylene Concentration (IEC)

In general, and especially for older cultivars, IEC of 1 ppm is considered to be the ultimate threshold above which fruit ripening and flesh softening are initiated and progress rapidly. Harvest for long-term storage should be completed before 20% of the apples have an IEC higher than 0.2 ppm. More recent cultivars, such as ‘Honeycrisp’, do not always follow that rule. ‘Ambrosia’ is low producer of ethylene, so the presence of ethylene is more important than exact concentration.

Starch-Iodine Test

Using the starch-iodine test, most apples destined for long-term storage should have 100% of the core tissue starch degraded (no stain) with greater than 60% of the flesh tissue still having starch present (stain). Again, recent cultivars do not always follow that rule, such as ‘Honeycrisp’. It is also important to note that not all apples mature and ripen in the same manner each year, and often there will be a need to compromise between correct maturity and the required firmness and sugar levels for market. 

Table 1 represents harvest guidelines for apples destined for long-term CA storage. Extreme weather during the growing season can influence fruit maturity, so actual values may vary during such seasons. Of course, you also need proper color to market the fruit. 

Table 1. Starch index values, firmness and internal ethylene concentration at harvest for apples going into long-term storage.

Cultivar	Starch Index (1-8)*	Firmness (lb)	Internal Ethylene (ppm)
Ambrosia	2.5 – 4	> 17	less than 1
Cortland	2.5 – 3.5	> 15	> 0.2 in
Crispin / Mutsu	3.5 – 4.5	> 17	> 0.2 in
Delicious (Red)	2.5 – 3.5	> 17	> 0.2 in
Empire	2.5 – 3.5	> 17	> 0.2 in
Gala	2.5 – 3	> 18	less than 1
Golden Delicious	3 – 4	> 16	> 0.2 in
Honeycrisp	~ 5	> 15	Not useful
Idared	3 – 4	> 15	Not useful
McIntosh	2.5 – 3.5	> 15	> 0.2 in
Northern Spy	2.5 – 3.5	> 18	>0.2 in

Common Controlled Atmosphere Storage Regimes for Apples

Table 2 summarizes the oxygen, carbon dioxide and temperature regimes for controlled atmosphere storage of common cultivars.

Table 2. Common controlled atmosphere storage regimes for apples

Cultivar	O2 (%)	CO2 (%)	Temp (oC)	Comments
Ambrosia	1.2-1.7	1-1.5%	0.5-1	less than 1% O2 with fruit monitoring (SafePod, etc..); slow cooling with 1-MCP
Cortland	1.5-2.5	1.5-2	0.5-2	Highest temp with 1-MCP; sensitive to CO2
Crispin / Mutsu	1.5-2.5	1.5-2.5	0-0.5	–
Delicious (Red)	1-2	1-2	0-0.5	less than 1% O2 fruit monitoring (SafePod, etc..)
Empire	1.5-2.5	1-2	2	Extremely sensitive to CO2; if  not treated with DPA keep CO2 st month
Fuji	1.5-2	0.5-1	0-1	Sensitive to CO2; delay CA with 1-MCP
Gala	1-2	0.5-1.5	0.5-2	Highest temp with 1-MCP; less than 1% O2 with fruit monitoring (SafePod, etc..)
Golden Delicious	1-2	1-2	0-1	less than 1% O2 with fruit monitoring (SafePod, etc..); slow stepwise cooling with 1-MCP
Granny Smith	1.5-2	0.5-2	0-1	less than 1% O2 with fruit monitoring (SafePod, etc..)
Honeycrisp	2-3	1-3	3 (after conditioning at 10oC for 7 days)	Delay CA for 1st month
Idared	1.5-2.5	1.5-2.5	0-1	–
Jonagold	1.5-2.5	1.5-2	0-1	Highest temp with 1-MCP
McIntosh	2.5	2 for 1st month, then 4.5	3	Sensitive to CO2 with 1-MCP
Northern Spy	1.5-2.5	1.5-2	0-0.5	Sensitive to CO2
Spartan	2-3	2-2.5	0.5-1	–