Northwest Michigan apple maturity report – September 23, 2015

Honeycrisp and McIntosh developed fairly quickly in recent extended, summer-like weather.

A cool and wet early September gave the northwest a taste of autumn; however, these conditions have transitioned into a warm and pleasant harvest season. This is our fourth week of apple maturity testing at the Northwest Michigan Horticultural Research Center (NWMHRC), and maturity has progressed fairly quickly since last week. Most apple varieties tested last week were not mature, and this week a few blocks of McIntosh and Honeycrisp are close or ready for harvest. Of McIntosh, the Linda Mac apples that we sampled had the highest average starch indices between 4 and 5, while other McIntosh varieties, including Red Max and MacSpur, were very close to mature with a starch index of about 3.

As mentioned in our previous report, the northwest has been behind this year’s McIntosh predicted harvest date of Sept. 20. Some growers are planning to start the first picking of Honeycrisp this week; sorting through fruit to find marketable apples has been a challenge in hail-damaged blocks. We have found low incidences of bitter pit in Honeycrisp; however, there have been reports of some orchards with bitter pit concerns.

Color continues to look good in all varieties. In particular, many Golden Delicious apples are beginning to take on a nice pink cheek. Overall size also looks good for most varieties with the exception of Gala that are usually on the small side in our region, particularly in blocks where optimal thinning was not achieved. Firmness of McIntosh has continued to decrease, but Honeycrisp has been holding steady since last week, which is promising, considering the fast transition in starch indices of this variety in other regions of the state.

Brix levels of most varieties have risen in the last week, and the predicted weather forecast should continue to favor sugar development. Although Jonagold are not yet testing in the mature range, brix levels are high in contrast to the low starch index readings. We have also observed some varieties with moldy core during this season’s apple testing.

Summary of northwest Michigan apple maturity samples taken Sept. 21, 2015


Color % (range)

Firmness lbs. pressure (range)

Starch (range)

Brix (range)


77.5 (63.0-92.5)

20.2 (20.1-20.5)

1.7 (1.3-2.3)

10.7 (10.2-11.1)


86.0 (61.5-99.0)

16.9 (15.8-19.3)

2.9 (1-4.8)

12.3 (11.2-12.8)


76.0 (71.0-86.0)

16.3 (16.1-16.7)

3.5 (1.5-5.1)

12.0 (10.5-13.2)

Golden Delicious

13.5 (11.5-15.5)

17.4 (17.4-17.4)

2.3 (2.1-2.4)

11.8 (11.6-11.9)


56.5 (53.0-60.0)

18.4 (18.2-18.5)

1.1 (1.0-1.1)

13.2 (13.1-13.3)

Gala (three samples). Galas have held firmness, and brix levels and starch indices have remained similar to last week. Color has continued to improve this week. Although these apples are not yet mature, warm conditions could hasten Gala development in the coming week.

McIntosh (four samples). Some McIntosh blocks are mature while others are very close to maturity based on results from brix and starch tests.

Honeycrisp (three samples). Maturity is variable within trees, and spot-picking of Honeycrisp will likely begin this week in northwest Michigan.

Golden Delicious (two samples). Golden Delicious are approaching maturity with an average starch index of 2.3 and brix level of 11.8.

Jonagold (two samples). This variety is not yet mature. While starch levels are low, brix levels are higher than expected.

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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