Tree Fruit Newsletter — September 16, 2024
Maturity Report and Storage Reminders
Peaches
Peaches ready this week: 2nd picking for Messina and 1st for Autumnstar. Both are good varieties.
We are also picking Castleton plums.
I am finding much less brown rot now that the weather has turned dry. The quality of peaches after a week in cold storage is also better than I expected considering the chilling sensitivity of this fruit. We store our peaches at 38 °F which is above what is recommended.
Apples
McIntosh has continued to ripen, but still seems ok for long-term storage. This is based on starch index and the lack of fruit drop when I shake limbs. However, one of our blocks of spur type Macs had a small amount of fruit drop after limb shaking. This indicates that McIntosh will soon be too ripe for long-term storage.
Gala at Highmoor Farm is almost fully ripe. 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, but will develop some internal browning if stored longer than six months.
Honeycrisp has been behind McIntosh in its ripening this year. Some blocks have reached a stage of maturity where they are suitable for long-term storage. The risk of bitter pit decreases when the starch index passes 5 and the Delta Absorbance readings decrease below 0.8. Most blocks are not past this yet at Highmoor Farm. 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.
In some blocks, Honeycrisp has reached the stage where they are highly susceptible to chilling injury in storage, so conditioning is critical now. To condition, hold apples at 50 to 70 °F for five days before putting into cold storage at 36 to 38 °F. You could also do a stepwise decrease in temperature during the first week of storage to lessen the risk of chilling injury after a shorter conditioning period. Don’t skip the conditioning. Because of the greater risk for bitter pit this year, I am recommending cold storage at temperatures of 36 °F with properly conditioned Honeycrisp. 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: When conditioning Honeycrisp in an enclosed room, the oxygen concentration can decrease to the point where human suffocation can occur. Ventilate these rooms before entering.
Cortland is starting to ripen in some blocks but has not reached a stage that is best for long-term storage. This variety is prone to superficial scald and bitter pit, both of which are more severe when fruit are harvested too soon. It’s ok to harvest for immediate sale if your customers find the quality acceptable.
| Variety | August 26 | August 30 | September 5 | September 10 | September 16 |
|---|---|---|---|---|---|
| Zestar! | 3.4 | 4.8 | — | — | — |
| Gala (Fulford) | — | — | 2.2 | 3.2 | 3.0 |
| McIntosh (Roger’s) | 2.4 | 3.1 | 3.6 | 4.5 | 4.7 |
| Macspur | — | — | 3.9 | 4.5 | 4.8 |
| Honeycrisp | 1.0 | 1.2 | 2.8 | 4.2 | 4.8 |
| Cortland | — | — | — | — | 1.5 |
| Royal Red Cortland | — | — | — | — | 1.2 |
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.
| Variety | September 5 | September 10 | September 16 |
|---|---|---|---|
| Gala (Fulford) | 0.76 | 0.70 | 0.55 |
| Honeycrisp | 1.12 | 0.88 | 1.04* |
*Honeycrisp blocks at Highmoor Farm were harvested once so remaining fruit are less mature than last week’s average.
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.
Renae Moran
University of Maine Cooperative Extension: Tree Fruits
PO Box 179
Monmouth, ME 04259
(207) 933-2100
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