Northwest Michigan apple maturity report – Sept. 2, 2020

Most apples are sizing nicely, but starch index readings suggest maturity is still a way off.

General apple harvest comments

As mentioned in yesterday’s Northwest Michigan Regional Report, fall is in the air. The weather conditions have been much cooler, both day and nighttime temperatures, compared with earlier August temperatures. Nighttime temperatures are cool and are getting down in the mid-50 degrees F, and these cool conditions will be excellent for coloring up apples. Weather conditions have been relatively dry with the exception of heavy rains last Wednesday (August 26th) which brought over 2.5” to the NWMHRC. Additionally, the region received some surprise variable rainfall last evening; the NWMHRC Enviroweather station recorded 0.34”. 

Overall, the apple crop looks good for the region. There are some varieties that look lighter than anticipated, but the quality is excellent at this time. Growers had a mostly successful thinning season, but there seemed to be a lot of natural drop after the thinning window that resulted in a lighter crop in some blocks. For example, we conducted precision crop load management sampling in our 3-year old Honeycrisp block at the NWMHRC and our computer output showed that we did not quite make our target number of fruit (still too many fruit, but we were nervous to thin again with all the natural drop). When we went out to take samples from that block, some of the trees that were tagged had no fruit on them. This observation suggests that the fruit dropped after our thinning window. We have also observed that other blocks of Honeycrisp near the NWMHRC are on the lighter side. 

At this time, most of our varieties tested still have a starch removal index in the 1-1.5 range indicating that we have some time before the fruit is ripe. Overall, color on most varieties in most blocks is looking excellent. At this stage of development, there are pretty apparent differences in color in trees that have been pruned well compared to trees that are hairier. From our fruit team call this morning, size may be variable in blocks that have irrigation compared to those that do not. However, size is looking pretty good in our region at this time. 

Pest activity has slowed recently with the exception of brown marmorated stink bug. This year is the first season that we have trapped this pest adjacent to an apple block at the NWMHRC. Feeding damage from this pest can be difficult to distinguish from apple maggot and bitter pit. There is some suspected feeding injury on Honeycrisp at the research station; the darkened depressions are along the shoulder of the fruit which is usually a good indicator that the damage is not bitter pit which is usually along the calyx end of the fruit. 

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

Variety

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

GingerGold

12.5%

19.8

1.2

11.1

SweeTango

46.5%

17.8

1.35

12.3

Honeycrisp

41.3% (15-70)

19.2 (16-23)

1 (1-1.5)

10.0 (8.6-10.8)

McIntosh

83% (60-100)

18.9 (16-22)

1.1 (1-1.5)

10.25% (9.6-11)

 

GingerGold maturity sampling for the harvest season

Sample date

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

Sept. 1, 2020

12.5%

19.8

1.2

11.1

We sampled one block of GingerGold this week. The apples are firm with relatively low starch conversion and degrees brix at this time. However, some growers have started spot picking the riper apples on the trees. Apples are starting to eat pretty well but obviously still have starch in them.

SweeTango maturity sampling for the harvest season

Sample date

Color % (range)

Firmness lbs. (range)

Starch (range)

Brix %

Sept. 1, 2020

46.5%

17.8

1.35

12.3

One sample of SweeTango was taken this week and the apples are starting to ripen but are not ready for harvesting. On the tree, these apples are deceiving as the exposed side has nice color, but shaded portions of the fruit and fruit on the interior are still green. 

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)

We sampled three Honeycrisp blocks this week, and this variety is not yet ready for picking. The apples are firm with relatively low degrees brix and percentage color at this time. Time and cool evenings are needed to help this variety ripen.

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)

McIntosh color is lovely, but apples from our two samples were not yet ready for eating. We have noticed some blocks where apples are starting to push off the tree.

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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