Tree Fruit Newsletter — September 15, 2026
In this newsletter:
- Maturity Report
Maturity Report
Peaches
We have a few more varieties yet to harvest. Glowingstar was picked late last week. Messina will be ready to harvest later this week.
Apples
Honeycrisp apples taste ready for a ‘first pick’, but are still not ready for long-term storage because the risk of bitter pit is greater in fruit that are less mature. One of the apples we cut open today had water soaked areas in the outer cortex. This is similar to water core which occurs at the end of harvest, but shows up in the apple flesh closer to the peel. Pay attention to the number of fruit with this disorder when you begin picking for storage because apples with severe water soaking will turn brown.
Gala maturity has advanced to the point where harvest for long-term storage should be completed soon.
McIntosh (spur-type) fruit are ready to pick for long-term storage based on starch index. IAD indicates a delay in maturity compared with starch index, but not enough data has been collected for solid conclusions with this relatively new maturity index. Limb shaking caused a small number of fruit to drop, but this is most likely from the prolonged dry spell rather than advanced maturity. The non-spur (Roger’s) strain is also ready to pick for long-term storage. Our Mac blocks have not been treated with ReTain or Harvista.
Starch index for Macoun and Cortland indicate the early stages of starch breakdown.
Starch index is based on iodine staining of starch in apples cut in half. Starch breakdown begins in the core and progresses outward to the peel as apples ripen. Each progressive stage of breakdown is assigned a number from 1 to 8 with 1 indicating none and 8 indicating complete breakdown.
| Variety | Starch Index 9/3/25 | Delta Absorbance* (IAD) 9/3/25 | Starch Index 9/9/25 | Delta Absorbance* (IAD) 9/9/25 | Starch Index 9/14/25 | Delta Absorbance* (IAD) 9/14/25 |
|---|---|---|---|---|---|---|
| Gala | 2.6 | 0.95 | 2.6 | 0.74 | 6.0 | 0.37 |
| Honeycrisp | 1.0 | 1.42 | 2.1 | 1.37 | 5.3 | 0.99 |
| McIntosh, spur-type | 3.0 | 1.95 | 3.7 | 1.89 | 5.0 | 1.88 |
| McIntosh, non-spur | – | – | 3.9 | 2.04 | 4.5 | 1.99 |
| Cortland | – | – | – | – | 1.2 | 1.89 |
| Macoun | – | – | – | – | 2.2 | 1.94 |
* 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 0.4 indicate sufficient maturity for storage. McIntosh IAD is much higher than in other varieties and has dropped below 1.80 at the start of harvest in the last two years.
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
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