Southwest Michigan apple maturity report – Sept. 5, 2018

William Shane<shane@msu.edu> - September 05, 2018

Apple ripening is proceeding rapidly in part due to recent heat.

Gala apples — Brookfield Gala. Photo by Bill Shane, MSU Extension.

General apple harvest comments

The relatively warm conditions have pushed apple maturation forward ahead of predictions. Other areas of the state with less rainfall have even earlier ripening than predicted.

Please be aware that samples we collect for this report are from the central Berrien County region, targeting more mature fruit on the outside of the tree canopy. Fruit in the interior of the tree will be less advanced than shown here. Sites with heavier soils and greater crop loads will generally be less mature.

Brown marmorated stink bug is damaging fruit in some area orchards, especially orchard sides close to woods, soybean fields, ravines and where natural hosts such as buckthorn, tree of heaven and mulberry have served as food sources.

Oriental fruit moth, codling moth, obliquebanded leafroller, apple maggot and San Jose scale are additional pests of concern at this time of year. Sooty blotch and flyspeck diseases are favored by the warm, wet conditions we have had in recent days. A few apples, especially light colored varieties, are infected by the fungal disease bitter rot, which appears as circular, dark fruit spots with salmon-orange, slimy spores most visible under rainy conditions.

Apple maturity in southwest Michigan for apples harvested Sept. 4
Variety	Firmness lbs. (range)	Starch (range)	Brix %
Gala	23.0 (21.3-25.0)	3.3 (1.8-4.6)	11.8
Honeycrisp	17.7 (16.2-19.0)	2.9 (1.6-2.9)	11.6
Jonathan	19.4 (18.2-20.0)	3.1 (3.0-3.2)	10.3

Individual variety results

Gala was sampled for the second week. Five of eight Gala sites tested starch conversion of 3 or greater. Target starch index for maturity for this variety is 3 and the predicted peak harvest date for central Berrien County is Sept. 10. Fruit firmness for all sites were well above the minimum firmness of 18 pounds recommended for long-term controlled atmosphere (CA) storage.

Last week starch readings averaged 1.5, so apple maturation has proceeded rapidly. Excellent firmness will allow harvesting to be delayed to wait for better size and color, however internal maturity for most sites is sufficient to allow harvesting.

Gala maturity sampling for the harvest season
Sample date	Firmness lbs. (range)	Starch (range)	Brix %
Aug. 28	25.4 ( 22.0-28.0)	1.5 (1.4-1.6)	11.8
Sept. 4	23.0 (21.3-25.0)	3.3 (1.8-4.6)	11.8

Honeycrisp was sampled for the second week. Starch conversion moved from an average of 1.8 last week to 2.9 for this week, with a few sites testing above the target mature starch index of 3.5 for this variety. The predicted peak harvest date is Sept. 18 for central Berrien County, which seems to indicate that some sites are maturing slightly ahead of prediction.

Brix for this week is 11.6, about the same as last week. Fruit firmness is averaging 17.7 pounds this week, with the general guideline of 17 pounds for best long-term CA storage. Watch this variety closely as both the firmness and internal starch conversion seems to be moving rapidly toward maturity.

Honeycrisp maturity sampling for the harvest season
Sample date	Firmness lbs. (range)	Starch (range)	Brix %
Aug. 28	20.0 (17.0-23.1)	1.8 (1.6-1.8)	12.0
Sept. 4	17.7 (16.2-19.0)	2.9 (1.6-4.8)	11.6

Jonathan was sampled for the first time this week. Target starch index for this variety this week is 3.5 and the predicted peak harvest date for central Berrien County is Sept. 26. Growers are rapidly harvesting this variety for taffy apples.

Jonathan maturity sampling for the harvest season
Sample date	Firmness lbs. (range)	Starch (range)	Brix %
Sept. 4	19.4 (18.2-20.0)	3.1 (3.0-3.2)	10.3

For additional comments from Randy Beaudry, MSU Department of Horticulture, read his general observations from MSU Apple Maturity Lab for 2018.

Normal and predicted 2018 peak harvest dates for apple varieties in southwest Michigan based on weather data at the Southwest Michigan Research and Extension Center, Benton Harbor, MI.
Variety	Normal date	2018 Predicted peak harvest date
Paula Red	Aug. 22	Aug. 20
Zestar	Aug. 22	Aug. 20
Gingergold	Aug. 20	Aug 18
McIntosh	Sept. 10	Sept 8
Gala	Sept. 8	Sept 6.
Early Fuji	Sept. 3	Sept. 1
Honeycrisp	Sept. 13	Sept. 13
Empire	Sept. 19	Sept. 23
Jonathan	Sept. 22	Sept. 24
Jonagold	Sept. 22	Sept. 24
Golden Delicious	Sept. 25	Sept. 27
Red Delicious	Sept. 28	Oct. 1
Ida Red	Oct. 5	Oct. 8
Rome	Oct. 5	Oct. 8
Fuji	Oct. 20	Oct. 22
Braeburn	Oct. 20	Oct. 22
Goldrush	Oct. 26	Oct. 28

Suggested firmness and starch index levels for long-term and shorter-term controlled atmosphere (CA) storage by variety.
Variety	Firmness (pounds)*			Starch Index*
Variety	Short CA	Mid-CA	Long CA	Mature	Over mature
McIntosh	14	15	16	5	7
Gala	16	17	18	3	6
Honeycrisp	15	16	17	3.5	7
Empire	14	15	16	3.5	6
Early Fuji	16	17	18	3	7
Jonagold	15	16	17	3.5	5.5
Jonathan	14	15	16	3.5	5.5
Golden Delicious	15	16	17	3	6.5
Red Delicious	16	17	18	2.5	6
Idared	14	15	16	3.5	6
Fuji	16	17	18	3	7
Rome	15	16	18	3	5.5

*Firmness is measured with a mechanical 11-millimeter wide probe inserted into the pared flesh of a fruit to a distance of 8 millimeters. Starch index is measured on equatorial cross section of an apple stained with iodine solution and rated using the Cornell University starch-iodine index chart for apples on a 1-8 scale (Predicting Harvest Date Window for Apples by Blanpied and Silsbey, Cornell Extension Bulletin 221.)

Looking for more? View Michigan State University Extension’s Apple Maturity page for regional reports throughout the state and additional resources.

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