Tree Fruit Maturity Report — September 2, 2025

September 3, 2025 Tree Fruit Newsletter

Maturity Report

Peaches

Peaches we are picking this week: Coralstar, PF17

Ripening of varieties has been out of the normal sequence this summer. Check varieties ahead of schedule because some seem to be ready to pick before expected.

Apples

McIntosh harvest indices are listed in the table below. Consider these values as the baseline because Macs are not yet ready to pick for storage. In years past, McIntosh has had a starch index of 3.0 a few weeks ahead of harvest.

Honeycrisp is showing signs of ripening in some fruits, but this is a sign of internal water soaking of the outer cortex. These apples are turning red, but have not developed an appropriate flavor or texture. Delta Absorbance (IAD) readings also indicate that Honeycrisp is not yet ready to pick for storage (see table below).

Paualred and Zestar! at Highmoor Farm have been picked.

Starch Index and Delta Absorbance collected on September 2, 2025 at University of Maine’s Highmoor Farm.
Variety Starch Index Delta Absorbance* (IAD)
Gala (Fulford) 1.4 1.13
Honeycrisp 2.0 1.21
McIntosh (standard) 3.0 2.02
McIntosh (spur type) 2.9 1.89
Cortland 1.0 1.87

* IAD is a measure of chlorophyll breakdown in the peel which parallels ripening. Numbers decrease as fruits ripen. Gala and Honeycrisp readings between 0.8 and 0.3 indicate sufficient maturity for storage. Mac and Cortland generally have much higher numbers than Honeycrisp and show a small decrease in IAD as they ripen.

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: partially ripe, but prone to disorders in long-term storage.

4: typically ready to pick for long-term storage.

5 – 6: indicates good flavor and ready for general harvest or harvest for short-term storage.

7 – 8: indicates fully ripe, too ripe for long-term storage.

 

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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