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We have been testing starch levels in McIntosh this week. All starch-index values appear much higher than normal (that is, starch levels are lower than normal). The 15-year average suggests that index values of standard McIntosh strains should not reach 3.0 on average until about September 8, and of Marshall McIntosh not until September 5. We have passed these levels, and it is not yet September. Fortunately, maturity is not as advanced as the starch-index values suggest. On Wednesday, August 30, 50 fruit each were harvested from Rogers Red McIntosh and Marshall McIntosh trees. Starch-index values averaged 4.5 for the Rogers and 4.0 for the Marshall, suggesting that the fruit were well into ripening. However, internal ethylene levels did not agree with this assessment, and internal ethylene is much much more accurate than the starch index for assessing maturity. No Rogers fruit was producing detectible ethylene, and only one Marshall fruit (out of 50) was. In most years, about 15% of the fruit will be producing significant amounts of ethylene when the average starch index value is 3.0.
It is well known that a cool, wet, and cloudy month before harvest can alter starch levels in fruit. Specifically, less starch is produced under these conditions, so when fruit begin to mature, starch will disappear sooner than normal. This likely is the reason for the abnormally high index levels (that is, abnormally low levels of starch) this year. Because of the is problem, starch-index values cannot be relied upon to assess maturity this year. Growers should use other methods to make this assessment.
For McIntosh, there appears to be no reason to expect that maturation is much earlier than normal, but pay careful attention to color development, drop, and eating quality.
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Date |
Location |
Starch Index Value |
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8/28 |
Deerfield |
3.2 |
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Shelburne |
3.4 |
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Colrain |
2.4 |
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Hawley |
2.0 |
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8/29 |
Belchertown |
4.1 (Rogers) |
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4.2 (Macspur) |
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8/30 |
Belchertown |
4.5 (Rogers) |
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4.0 (Marshall) |
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Eastern Mass. |
3.5-4.5 |
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, Bill Coli, and Duane Greene except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
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