Southwest Michigan apple maturity report – September 18, 2013

Recent, cool weather has improved red coloring of Gala, Honeycrisp and Jonagold. Tests this week show Golden Delicious and Red Delicious are generally not ready for picking in southwest Michigan.

General comments

Early Fuji, Honeycrisp and Gala in the area are testing mature and being harvested as labor and fruit coloring permits. Most area Jonathans and Empires have been harvested for taffy apples. Marmorated stink bug numbers continue to be low and are being found primarily associated with Russian olive trees in the Stevensville, Mich., area.

Summary of Berrien County apple maturity samples taken Sept 16-17, 2013.


Date sampled

Firmness lb. pressure (range)

Starch conversion (range)

Brix (range)


Sept. 16-17

16.9 (15.8 - 17.5)

5.6 (4.6 - 6.8)

13.6 (12.6 - 14.8)

Golden Delicious

Sept. 16-17

17.4 (15.7 - 19.4)

1.7 (1 - 4)

13.5 (12.1 - 14.4)

Red Delicious

Sept. 16-17

17.6 (16.9 - 19)

2.0 (1.8 - 2.2)

10.6 (9.9 - 11.1)

Jonagold (three sites sampled Sept. 16-17)

This variety has moved quickly over the past week. Firmness this week is averaging 16.9 pounds (15.8-17.5) compared to last week’s value of 18.7 pounds. Starch conversion this week is 5.6 (4.6-6.8) compared to last week’s 3.3, and brix is 13.6 (12.6-14.8) compared to last week’s 13.2. Blush has improved greatly with the recent cool weather, but background is still mostly green.

Predicted peak harvest date for 2013 for mid-Berrien County is Sept. 22. The target fruit conditions for long-term CA storage is 17 pounds and a starch conversion index of 3.5. Internal ripening (pressure and starch conversion) of this variety is ahead of the predicted date with all three sites testing mature according to the starch conversion index, but some growers will wait for sufficient skin color for their markets.

Golden Delicious (six sites sampled Sept. 16-17)

We are seeing nice quality fruit in the area with pretty blush developing on Smoothee. Readings this week are firmness of 17.4 pounds (15.7-19.4), starch conversion of 1.7 (1-4) and brix of 13.5 (12.1-14.4). For this variety, the target fruit conditions for long-term CA storage are 17 pounds firmness and minimum of 3.0 on the starch conversion.

Predicted harvest date for central Berrien County is Sept. 25. A few Golden Delicious blocks have reached sufficient maturity for long-term CA for the most mature fruit in the orchards, but most blocks are not quite mature.

Red Delicious (seven sites sampled Sept. 16-17)

Red Delicious have nice appearance this year with a classic lobed shape. This week’s tests show firmness of 17.6 pounds (16.9-19), starch conversion of 2.0 (1.8-2.2) and brix of 10.6 (9.9-11.1). Predicted harvest date for central Berrien County is October 3, 2013. For this variety, the target fruit conditions for long-term CA are fruit firmness of 18 pounds and minimum of 2.5 for the starch conversion index. The samples indicate that Red Delicious are immature according to the starch conversion index.

Pressure and starch conversion target indices for apple maturity for selected varieties




Short CA*


Long CA


Over mature







Golden Delicious






Red Delicious






*CA = controlled atmosphere storage

The Southwest Michigan Apple Maturity Report is produced by: Bill Shane, MSU district Extension educator for fruit and marketing, Benton Harbor, 269-944-1477 ext. 205, fax 269-944-310; Diane Brown, Berrien County Extension educator, Benton Harbor, 269-944-4126; and Mark Longstroth, district Extension educator for fruit and marketing, Paw Paw.

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

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