Tree Fruit Newsletter — September 13, 2023

A tropical storm or hurricane is expected in the area this weekend. Strong winds will likely knock fruit off trees and cause fruit bruising when the wind blows branches around. Winds could be strong enough to blow over trees. Best of luck to everyone this weekend.

Maturity Report

McIntosh. Starch breakdown continued with a small decrease in Delta reading. Flavor has improved. The spur-type strain appears ready to pick for storage. Limb shaking showed no sign of drop.

Honeycrisp. Starch breakdown continued, and Delta numbers decreased. This variety is showing large block-to-block variation, so check each orchard block when scheduling harvests for storage. Some are ready to pick for storage. When the ground color is green, they have a higher risk of bitter pit. Based on taste tests, stored apples could quickly lose flavor.

Gala. Based on Delta readings, these apples are ok to harvest for storage. Size is still small, but we have substantial freeze damage in this block. Also, odd internal browning.

Cortland. Flavor has improved, but Cortland is not ready to harvest for storage. OK to harvest for immediate sales at farmstands for customers who like them green and sour.

Empire. Starch breakdown continued, and Delta numbers decreased. As with Gala, size is small and does not seem to be increasing.

Variety Testing Results

Variety Starch Index Delta Absorbance meter reading*
Gala 2.6 0.80
McIntosh standard Strain 4.0 1.85
McIntosh spur type 4.5 1.84
Honeycrisp 3.6 1.14
Cortland 1.3 1.54
Empire 1.8 1.53

*Delta reading is 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 0.4 indicate sufficient maturity for storage. Standards for other varieties have not been determined. McIntosh readings will remain higher than other varieties throughout the harvest.

Starch index is a measure of starch breakdown, so the index number increases as fruit ripen.  Macs are generally good for long-term storage when starch index reaches 4.0, but starch index may be off this year. Honeycrisp are usually good for long-term storage when starch index passes 4.5.

Renae Moran
UMaine Cooperative Extension Tree Fruits Program
University of Maine Cooperative Extension
PO Box 179
Monmouth, ME 04259
(207) 933-2100

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