MSU Extension Apples

General comments

In the Grand Rapids, Michigan, area, apple maturity seems to be running close or slightly ahead of our 2020 predicted apple harvest dates for Honeycrisp. Keep in mind these predicted dates are for peak harvest, so some fruits might be ready ahead or behind these dates as we move through maturity. Many growers are saying they are picking a bit longer than expected as fruit size is excellent this year.

Some late season pests are getting in the way of harvest, woolly apple aphid in particular. There really is not much you can do this late in the season to knock them back; management should have been done in June or early July to be most effective. It is likely they overwintered quite well due to the mild 2019-20 winter. There are many beneficials in every woolly apple aphid colony I see, and they will help curb numbers for next year. I found a great resource for woolly apple aphid from Washington State University, and there are no silver bullets in it to help this late in the season.

Brown marmorated stink bug damage continues to be found in various apple blocks. Overall, it seems that damage is slightly higher than we have experienced in the past. I continue to find the occasional late instar nymph or adult feeding on fruits, particularly towards the end of the day. Trap numbers creep up a little every week but seeing more brown marmorated stink bug on fruit and in trees concerns me.

Variety sampling results

Strains are noted where applicable. We try our best to collect samples from blocks untreated with harvest management products.

The past week has been a big week for Gala harvest where color and size are acceptable. Our predicted date for peak Gala harvest was Sept. 14. Color continues to be very good to excellent on most Gala strains this year. Our red color readings are up slightly this week compared to last week. Background color is a solid 1 (yellow) for all fruit sampled. Fruit firmness continues to be much higher than normal and continues to decrease slowly as expected from an average of 21.4 pounds last week to 19.3 pounds this week.

The sample readings in the table below are untreated fruit. Fruits sampled here are not treated with ReTain and data indicates these fruits are in the prime window for long-term controlled atmosphere (CA) storage right now. Where ReTain has been used, the internal ethylene continues to be low as expected and desired.

The predicted harvest date for McIntosh in the Grand Rapids area is Sept. 19 and our first samples are showing that date should be accurate for the peak of harvest. Internal ethylene is very, very low with no fruits over the 0.2 ppm climacteric indicating immature fruit. Our sample is from Linda Mac, so the 85% color is perhaps redder than standard Macs. However, all McIntosh strains have great color this season and it will only continue to improve with the forecasted weather with clear, sunny days and cool nights.

The background color has changed for the better at 2.6 this week down from 3.9 last week. Fruit firmness continues to be very high at 17 on average, down from 18.3 pounds last week. Starch clearing ranges from 4 to 6 this week for an average overall of 4.8, which is an improvement from last week. Brix readings are similar to the last few weeks and averaged 12.9 this week. This is typical for McIntosh. Macs are in the long-term CA storage window right now.

Our predicted date for traditional Honeycrisp is Sept. 23 for peak harvest. First pickings where color is good started this week, so perhaps our predicted date is a few days on the late side this year. Internal ethylene is high for Honeycrisp as usual. Red color appears to have dropped this week, but that is due to our sampling site being harvested for first pick and only greener fruits were left to choose from. The background color is an average of 2.

Fruit pressure is still very good at an average of 15.8 pounds, down from 17.5 pounds last week. Starch clearing looks to have declined, from 4.9 to 3.8, and this is again due to first pick leaving only greener, immature fruits for this weeks’ samples. Brix also seemed to have declined, but for the same first pick reason.

The predicted harvest date for peak harvest of Empire in Grand Rapids is Sept. 28. This week’s samples continue to show fruit to be changing a bit, but still very immature.

We sampled Jonathan and Jonagold for the first time this week. Our predicted harvest date for Jonathan and Jonagold is Sept. 30 and that date appears to be accurate for the peak of harvest, with some color picking in Jonagold starting ahead of that date where color is adequate. I have seen some Jonathans harvested, likely for the taffy apple market. Fruit firmness for Jonathan and Jonagold is excellent, but not as high as typical this early in the game.

Cortland is immature with starch readings of all 1s. Color is excellent for these Red Corts. Brix are outstanding for Cortland at 13.4 on average – we rarely see brix at that level when fruit is mature, let alone a couple of weeks out. Harvest of Cortland is usually around between Jonagold and Red Delicious and they need some time yet to mature.

Many changes in apple physiology occur over time as fruit become more mature—starch is converted to sugar; seeds turn a darker color; acidity decreases; chlorophyll levels decrease; respiration increases; cell walls weaken; fruit begins to soften; and ethylene production increases. Our MSU Ridge Apple Quality Lab and the MSU campus Beaudry Lab measure these and many other factors to help you make harvest management decisions:

Apple maturity sampling parameters

• % fruits with internal ethylene over 0.2 ppm = indicates when ethylene begins to influence fruit ripening and it cannot be held back easily after this is reached.
• Color % = the visual percentage of red color from 0 to 100; range is of all fruits tested
• Background color: 5 = Green, 1 = Yellow; range is of all fruits tested.
• Firmness in pounds pressure
• Starch: 1 = all starch, 8 = No starch; range is of all fruits tested. Using Cornell Starch Iodine Index Chart.
• Brix = % sugar

We are graciously funded by the Michigan Tree Fruit Commission, Michigan Apple Committee, Michigan State Horticultural Society and Michigan State University Extension. Many thanks to all the growers and industry representatives that donate to our program.

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