Northwest Michigan apple maturity report – September 9, 2015

Recent weather has delayed apple development and estimated picking dates.

Overall, there has been little change in apple maturity of Gala and McIntosh varieties since last week. Our samples of these varieties show a slight decrease in firmness, and starch indices, color and brix levels have increased a little. In contrast, maturity parameters of Honeycrisp indicate that these fruit are ripening faster than the Gala and McIntosh that were tested this week. However, many of the Honeycrisp that were sampled were hail damaged, and damaged fruit have higher ethylene production that likely impacts this week’s maturity readings. Therefore, this Honeycrisp data may not be representative of the maturity of undamaged Honeycrisp apples.

We received 0.83 inches of rain Thursday, Sept. 3, at the Northwest Michigan Horticultural Research Center (NWMRHC) that helped fruit size. Yesterday, Tuesday, Sept. 8, was also wet with the periodic heavy downpours and in total we accumulated 1.58 inches of rain at the station. The forecast is starting to look like typical fall weather in northwest Michigan with cooler temperatures predicted for this week. Cool nights will be good for coloring apples and daytime temperatures should be comfortable for those picking apples as long as the rain holds off. Currently, there is a chance for rain and thunderstorms overnight tonight, Wednesday, Sept. 9, and possibly Thursday.

In the northwest, SweeTango harvest is predicted for this week and Gala harvest typically follows SweeTango by seven to 14 days depending on location and soil type. In other parts of the state, apple harvest is underway and apple development advanced quickly during hot conditions over the holiday weekend.

Summary of northwest Michigan apple maturity samples taken Sept. 9, 2015


Color % (range)

Firmness lbs. pressure (range)

Starch (range)

Brix (range)


51.5 (42-61)

22.1 (21.7-22.5)

1 (1-1)

10.2 (9.8-10.6)


82 (69-95.5)

19.4 (18.8-19.9)

1.2 (1-1.4)

11 (10.3-11.1)


49.4 (20-70.1)

17.5 (17-17.9)

1.6 (1-1.95)

11.5 (9.5-12.8)

Individual variety results

Gala – Not mature (two samples). Although pressure readings have decreased since last week, galas are still very firm at 22 pounds. Brix are on the rise, but starch indices are still low, indicating these fruit are not mature; the target starch index is 3. There has been little color change since last week.

McIntosh – Not mature (two samples). While these apples are still very firm, McIntosh are starting to soften and we are beginning to see higher starch indices. No change in the brix levels and very little change in color this week compared with last week.

Honeycrisp – Not mature (three samples). Compared with the other varieties that were sampled this week, Honeycrisp showed the greatest changes in maturity indicators. Honeycrisp firmness dropped by nearly 2 pounds to 17.5 pounds, starch index increased to 1.6 and brix levels also increased to 11.5. Note that many of the fruit that were sampled were hail damaged, which likely impacted ripeness data.

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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