MSU Extension Apples

General comments

In the Grand Rapids, Michigan, area, apple maturity continues to run close to 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.

Brown marmorated stink bug damage continues to be found in various apple blocks, and it seems damage is slightly higher than we have experienced in the past. We continue to catch nymphs and adults in traps and they are actively feeding in apples where numbers have been quite high in the past.

Variety sampling results

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

A great deal of the Gala blocks on the Ridge have been harvested. The only fruit we had left to sample has been treated with ReTain. Non-treated fruits are moving out of the long-term storage window and treated fruits lag behind a bit and need to harvested soon for long-term controlled atmosphere (CA) storage needs.

The predicted harvest date for McIntosh in the Grand Rapids area was Sept. 19 and some harvest is complete. Our fruits sampled this week were treated with ReTain. Red color seems to have peaked out at around 90%. The background color is more yellow at 1.7 this week compared to 2.6 last week.

Fruit firmness continues to be very good at 16.1 pounds on average, down from 17 pounds last week. Starch clearing averages 5.8 this week compared to 4.8 last week. Brix readings show improvement from 12.9 last week to 13.6 this week. Macs are still in the long-term CA storage window right now and will move to mid- to short term CA in the next five to seven days even with harvest management applications.

Our predicted date for traditional Honeycrisp is today, Sept. 23, for peak harvest, which is nearly on target—perhaps a day or two late as many Honeycrisp have found a bin in the last five days. It is estimated that first pickings took about two-thirds of the Honeycrisp from trees because red color is so good this year. Many will only need one more picking when color improves on interior fruit. Our sample this week has been treated with ReTain so take that into account.

Red color is still very good even though the reddest fruits have been harvested already. The background color is an average of 1.9. Fruit pressure is still very good at an average of 16.9 pounds and similar to last week. Starch clearing averages 7 with a wide range from 5 to 8 as is typical for Honeycrisp. Brix are still very good at an average of 13.6.

The predicted harvest date for peak harvest of Empire in Grand Rapids is Sept. 28. This week’s samples continue to show fruit moving towards maturity, but still a bit immature for the best long-term CA criteria—they need three or four more days to get to the desired starch clearing. The red color is very good this year averaging 76% this week. The background color is still green at 2.8—not bad, but not quite there yet.

Firmness is excellent at 18 pounds pressure. Starch clearing is at 3.3, up from 2.3 last week. Brix are good at 12.7, and a few more days should improve brix greatly. The predicted harvest date of Sept. 28, give or take a few days, will be a good target for first picking of Empire for long-term CA storage.

We added an early Fuji sample this week. They are ready for harvest when you feel the color is right and you have the time to take them.

This is the second week of sampling for Jonathan and Jonagold. Our predicted harvest date for both 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. For both Jonathan and Jonagold, fruit color is good to excellent depending on the strain. Starch clearing and other maturity parameters indicate the target window for untreated fruit to go into long-term CA will be right around Sept. 30 as predicted.

Cortland is still immature, but changes are underway. There has been a definite uptick in internal ethylene for our RedCort sample with 90% of fruits over the 0.2 ppm climacteric compared to zero last week. Color is excellent at 92% compared to 82% last week. The background color is still quite green at 2.2. Firmness is very good at 16.7 pounds pressure, down slightly from last week’s 17.2 pounds.

The starch readings have changed only a bit from no starch clearing last week to a few 1s and ’s this week for an average of 1.9. Brix are improved from 13.4 last week to 13.7 this week, which is really quite high for Cortland this early. Harvest of Cortland is usually between Jonagold and Red Delicious and they need some time yet to mature, so that timing will be a good target for 2020.

Nova Spy is not a common variety. Our sampling this week show fruit changing in maturity only slightly. They probably need a week or more to improve.

The predicted harvest date for Golden Delicious in the Grand Rapids area is Oct. 2. Our first sample this week indicates that should be a good target date for peak harvest. Fruit is still immature.

This is our first week to look at Red Delicious. Fruits are immature as expected with a predicted harvest date of Oct. 6. Firmness is outstanding. Brix levels are also very good for two weeks out from first harvest for our sample. I often see brix around 10 this far ahead of harvest, so 12.3 is excellent.

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.