Tree Fruit Newsletter — August 22, 2024

In this newsletter:

• Maturity Report
• ReTain Instructions

Maturity Report

Peaches

Peaches we are picking now: Lucky 13, PF15A

Peaches we will pick next: Blazingstar, Starfire

Apples

Paulared starch index is 3.5. Ready for a general harvest at Highmoor Farm. Pay attention to preharvest intervals for recently applied materials.

Starch index is measured on a scale of 1 to 8 and is an indicator of fruit ripening. However, it can be influenced by variety, weather and crop load. Starch breakdown begins in the core and progresses to the outer flesh as fruit ripen, and this can be seen with an iodine stain.

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.

ReTain with NAA for Extended Fruit Drop Control

ReTain can be combined with NAA to prolong fruit drop control. For McIntosh, apply Retain at the full rate with an NAA product (Fruitone, PoMaxa) at 10 ppm (4 fl. oz. per 100 gals. dilute equivalent) three weeks before first harvest. A second application may be needed to prolong drop control of McIntosh.

Honeycrisp is less prone to early fruit drop and does not require as much ReTain for fruit drop control, and does not need the addition of NAA.

General use guidelines for ReTain include:

• Application timing will depend on how you want to manage the harvest. Application 4 weeks before the start of harvest will delay ripening in the “first pick” apples, but will wear off by the end of harvest. Application at 7 days before harvest will have little impact on ripening in the “first pick”, but will slow ripening in the apples that would be harvested last.
• Apply 21 to 7 days before anticipated harvest (7-day PHI). REI is 12 hours.
• Use one pouch (or less) per application; two applications are allowed.
• On Honeycrisp and Gala, consider using reduced rates — early application of ReTain can inhibit color development on these varieties.
• Use an organosilicone surfactant at a concentration of 0.05 to 0.1% (6.4 to 12.8 oz surfactant per 100 gallons water) with ReTain, do not apply when temperature exceeds 85 degrees F.
• Dilute applications are recommended, up to 2 X concentration.
• Avoid application when rain is expected within 12 hours.
• Do not apply to stressed trees.
• Avoid application with calcium chloride as phytotoxicity has been observed.

 

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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