Northwest Michigan apple maturity report – Sept. 16, 2020

Fruit is coloring nicely with the recent cool weather, and growers anticipate harvest of most varieties to begin in earnest this weekend and into next week.

General apple harvest comments

The overall weather pattern over the past week has been cool with some rainfall over the weekend. The weather has felt more like later in October than mid-September. Until yesterday, 15 September, the daytime highs have reached into the low to mid-60s. We have also had cool nights whereas the temperatures dipped into the low 50s degree F. We have had reports of temperatures dropping into the 40s in some lower sites and sites away from the water. Yesterday, temperatures went back up into summer-like temperatures, but are predicted to drop again after today. Thus far for 2020, we have accumulated 3298GDD base 42 and 2217GDD base 50. The degree day accumulations are close to our 30+-year averages: 3359GDD base 42 and 2208GDD base 50. We also had a bit of a soggy weekend. On Saturday, 12 September, the NWMHRC Enviroweather station recorded 0.59” of rainfall. 

Growers are eager to begin apple harvest for some of the key varieties this season. Fruit has good size and excellent color for this time of the year, and it is easy to see why growers are ready to get the ball rolling. However, our maturity testing is suggesting the fruit need more time to ripen. Some of the earlier varieties, such as GingerGold and Zestar, have been picked and are available at markets and stands. Growers are still waiting on color development and starch removal indices to rise before they begin to move into Gala and Honeycrisp blocks. Growers that grow SweeTango are harvesting this variety at this time.

There seems to be considerable variability in maturity in Gala blocks depending on the Gala strain. Some blocks we tested have excellent color, near 100%, while some older strains are at 70% color. As with color, the starch removal numbers are also variable in Gala by block and likely strain. There seems to be a bit of variability between apples in Gala as well. Some growers may be starting to spot pick some of their newer strains of Gala. Galas at the NWMHRC have excellent color and eat pretty well at this time. We anticipate beginning Gala harvest at the start of next week at the station.

At this time, the starch removal indices have increased since last week as the fruit is ripening. Many fruits have moved from the 1-1.5 range into the 2’s. Some individual samples are testing even higher in starch removal, but there is variability across those samples. Fruit is still eating green, but sometimes you can find an apple within the sample that is edible. There is also some variability in color between samples, but most samples from individual farms are more uniform. As mentioned above, Gala color differences are likely due to strain. Fruit are still relatively firm, but we did observe some drop in firmness this week compared to last week. Overall, fruit is looking excellent for most blocks across the region.

We found one brown marmorated stink bug at the station this week, but none in the other traps around the region. We have heard reports of some stinkbug damage in the region; stink bug damage can often be differentiated from bitter pit as the damage from the insect is often on the shoulder of the fruit. We have also observed considerable bird damage at the station in both our Gala and Honeycrisp blocks. Birds do seem to prefer Honeycrisp over Gala, even if the Gala are more highly colored than the Honeycrisp. We have seen bird damage both high and low in the canopy. Bird pecks high in the canopy are likely caused by crows while low damage is turkeys feeding from the ground. 

Apple maturity in northwest Michigan for apples collected on Sept. 1, 2020

Variety

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

Gala

88% (76-95)

21.2 (19.5-21.9)

1.5 (1.1-2.4)

11.3 (10.6-11.9)

Honeycrisp

72.3% (66-87)

18.4 (16.7-19.2)

2.0 (1.5-2.8)

11.0 (10.9-11.4)

McIntosh

81% (69-90)

17.15 (15.9-18.5)

3.0 (2.1-4.2)

11.5 (11.1-11.8)

 

Gala maturity sampling for the harvest season

Sample date

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

 

Sept. 8, 2020

82% (20-100)

21.3 (17-23)

1.9 (1-7)

11.2 (9-14.6)

 

Sept. 15, 2020

88% (76-95)

21.2 (19.5-21.9)

1.5 (1.1-2.4)

11.3 (10.6-11.9)

 

We sampled four blocks of Gala this week. Gala apples are pretty firm, and the firmness has remained consistent over the past few weeks. Most of the starch removal index readings are in the 1.5 range, but one sample had an average starch removal index reading of an average 2.4. Color in Gala is excellent in all samples with an average of 88% for all samples.

Honeycrisp maturity sampling for the harvest season

Sample date

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

Sept. 1, 2020

41.3% (15-70)

19.2 (16-23)

1 (1-1.5)

10.0 (8.6-10.8)

Sept. 8, 2020

51% (5-95)

18.6 (16-22)

1.2 (1-2)

10.4 (8.8-11.4)

Sept. 15, 2020

72.3% (66-87)

18.4 (16.7-19.2)

2.0 (1.5-2.8)

11.5 (11.1-11.8)

We sampled six Honeycrisp blocks this week, and this variety is still not yet ready for picking. Firmness has dropped in this variety compared to some of the other varieties; however, apples are still firm overall. Starch index readings are higher this week compared to last week, and most varieties are testing in the 2-range. All the samples need more color before harvest. Color is variable between blocks, but all samples will need to pick up more color before growers start to spot pick them.

McIntosh maturity sampling for the harvest season

Sample date

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

Sept. 1, 2020

83% (60-100)

18.9 (16-22)

1.1 (1-1.5)

10.25 (9.6-11)

Sept. 8, 2020

88% (60-100)

18.7 (14-23)

1.8 (1-4)

11.1 (9-12)

Sept. 15, 2020

81% (69-90)

17.15 (15-9-18.5)

3.0 (2.1-4.2)

11.5 (11.1-11.8)

We sampled four blocks of McIntosh this week. This variety is getting harder to find to sample as many blocks of McIntosh have been removed. As expected, firmness is this variety is lower than other varieties. This variety has more variability in starch removal compared to other varieties, but we did test McIntosh and Spur Macs in this sample. Fruit still has a green background and are eating green, but they are starting to take on the Mac flavor. 

Suggested firmness and starch index levels for long-term and shorter-term controlled atmosphere (CA) storage by variety.

Variety

Firmness (pounds)*

Starch Index*

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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