Tree Fruit Newsletter — September 10, 2024

Maturity Report

Peaches

Peaches we are picking now: Blushingstar, PF23 and Messina

Apples

McIntosh has developed some sweetness and should be good for immediate sales, if you have not already started selling them. At this stage, they should also be good for long-term storage, although susceptible to storage scald. Storage scald is prevented by fogging with diphenylamine and 1-mcp. Contact your chemical rep for more information on how to use these two postharvest materials. The Guide has a section on superficial scald.

Gala at Highmoor Farm is ready to pick for long-term storage. The starch index does not appear to follow ripening in this variety, so go by the Delta Absorbance readings listed below and by peel color change from green to pale yellow or cream color. This variety is not susceptible to storage scald, chilling injury or bitter pit.

Honeycrisp continues to ripen and has developed good flavor. Ripening is very uneven in this variety, so check ground color and look for signs that the peel is turning to a lighter shade of green with some signs of pale yellow-green. When picked too early, it is highly susceptible to bitter pit in cold storage. Unfortunately, the bitter pit prediction test is indicating a greater risk of bitter pit in storage compared to last year in some blocks. The worst block had 46% this year’s test, but several blocks had 0%. I am seeing a wide range in potential susceptibility to bitter pit this year among the various blocks in this test.

Honeycrisp will be developing susceptibility to chilling injury next week and should be conditioned prior to cold storage. To condition, hold apples at 50 to 70 °F for five to seven days before putting into cold storage at 36 to 38 °F. Because of the greater risk for bitter pit this year, I am recommending cold storage at temperatures of 35 to 36 °F, not warmer. Conditioning prior to cold storage substantially reduces the risk of soft scald and soggy breakdown, so storing a few degrees colder can reduce bitter pit incidence.

Reminder: Honeycrisp is sensitive to the elevated carbon dioxide that occurs in controlled atmosphere storage. Be sure to include enough lime in your CA rooms. This is also true of any variety treated with 1-MCP (Hazel, SmartFresh). Diphenylamine fogging helps to protect fruit against toxic levels of carbon dioxide.

If you have purchased Honeycrisp apples from another grower, there is a good chance that they have not been conditioned and are susceptible to chilling injury (soft scald and soggy breakdown). Honeycrisp can develop soft, brown spots on the surface in as little as three weeks in cold storage if they have not been conditioned first.

The following is a rough guide to what the starch index numbers mean for apple ripening:

1 – 2 indicates lack of starch breakdown and generally unripe.

3 – 4 indicates some sweetness developing and generally partially ripe.

5 – 6 indicates good flavor and ready for general harvest.

7 – 8 indicates fully ripe.

*A measure of chlorophyll breakdown in the peel and change in ground color from green to yellow. Numbers decrease as fruits ripen. Gala and Honeycrisp readings between 0.8 and 0.3 indicate sufficient maturity for storage. Standards for other varieties have not been determined.

Starch index and Delta absorbance readings indicate a more advanced stage of maturity this year compared with last year. The temperature models predicted a Sept. 7 start of harvest for McIntosh, but apparently the model is off by a few days this year.

 

 

Renae Moran

University of Maine Cooperative Extension: Tree Fruits

PO Box 179

Monmouth, ME 04259

(207) 933-2100

rmoran@maine.edu

 

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