When Will Apples Be Ready to Harvest?

Will wet soils bring the crop on sooner? What effect will cloudy skies have on maturity? Are we ahead or behind last year? One way to monitor the maturity development and answer these questions is using the starch-iodine test.

What you need: Assemble a testing kit to carry with you to evaluate your apples. You will need:

A shallow dish to hold the iodine solution
A sharp knife to cut apples
A squirt bottle of water to rinse off treated apples
Starch-sugar conversion charts for each cultivar (see below)
Paper towels and garbage bag
Paper and pen to record dates and results

Prepare the iodine solution: Contact your pharmacy to prepare a fresh batch - it's best to make fresh solution each harvest season. Store the solution in a dark coloured (or foil-wrapped) bottle, away from light.

Caution: Remember that iodine is poisonous. Correctly label the bottle and keep away from children and pets. Consider treated apples poisonous - do not feed to animals or use in composting. Prevent pets from licking the treated fruit.

Recipe to give to the pharmacist:

1. Dissolve 8.8 grams of potassium iodide in approximately 30 ml of warm water. Gently stir the solution until the potassium odide is dissolved.
2. When it is properly dissolved, add 2.2 grams of iodine crystals. Shake the mixture until the crystals are thoroughly dissolved.
3. Dilute this mixture with water to make 1.0 litre of test solution. Mix well.Starch-iodine chart: The most useful starch chart is the Generic Starch-Iodine Index Chart for Apples from Cornell University. This chart uses 1 to 8 values, as follows -

1 = 100% core stain and 100% flesh stain
2 = 50% core stain and 100% flesh stain
3 = 0% core stain and 100% flesh stain
4 = 0% core stain and 80% flesh stain
5 = 0% core stain and 60% flesh stain
6 = 0% core stain and 40% flesh stain
7 = 0% core stain and 20% flesh stain
8 = 0% core stain and 0% flesh stain

It is can be used for all apple cultivars and it is important to note that this starch chart is the one that all maturity recommendations for the use of SmartFresh (1-MCP) are based on. Copies may be obtained from AgroFresh directly, or through Jennifer DeEll at Jennifer.DeEll@ontario.ca.

The original chart can be found online on p. 9 to 11: http://ecommons.library.cornell.edu/bitstream/1813/3299/2/Predicting%20Harvest%20Date%20Window%20for%20Apples.pdf

How to do the test: Select representative trees in crop load and vigour, and avoid the use of end trees and outer rows. Sample from different sides of the trees and select apples of typical size and color. Test apples soon after collection and no longer than 12 hours after collection. Cut apples in half through the equator, dip the cut edges in the iodine solution, wait at least one minute, rinse with water, and compare to the chart.

This is a simple test to determine how much starch has changed to sugar - and if the apples are ready to harvest. In general, values just over 2-3 are optimum for harvesting apples destined for long-term storage, whereas slightly higher values are optimum for short-term storage or immediate consumption.

Honeycrisp is unique, in that starch index values of 6+ are best.