MSU Extension

General comments

This is the fourth Michigan State University Extension apple maturity report from the Grand Rapids, Michigan, area fruit team. Growers in the area are very busy picking several varieties at once, including Gala, Honeycrisp, McIntosh, Jonathan and many others. Dry weather has allowed growers to keep up with harvest tasks pretty well, but as we hit the peak of many varieties at once, it can feel like you are behind.

Unusually hot weather is on tap for the next several days and this will push maturity even faster and bring special concerns not common to the end of September. Please see the special article this week, “Hot, hot apple harvest concerns,” on dealing with heat in harvested fruit. Also, play close attention to heat stress in the humans working on your harvest with this hot spell.

From the additional sampling for this week, it now looks like our predicted harvest dates for mid- to late ripening varieties on the Ridge might be a little too late. The heat and dry weather is moving maturity along a bit faster than those predictions, which were made back in July.  The dates in the table below are guesstimates for the peak of harvest with no harvest management applied. Also, keep in mind that trees with a lighter crop load will tend to ripen earlier and trees with a heavy crop load will show a delay in maturity.

There certainly is a wide variability in fruit set this season due to the very long, drawn out bloom period and crop losses due to freezes. If you have any questions about maturity, please let me know and I’d be happy to run a sample through our lab.

Variety sampling results for the general Grand Rapids area

Gala harvest continues on the Ridge with about 75 percent harvested. Color in our samples is down slightly due to having less fruits to choose from in our sampling blocks, but overall color has been excellent this season. Background color is holding in the 1 to 3 range. Still good, but declined from 20.3 pounds last week to 17.4 pounds this week, a rather significant drop compared to the past few weeks. The starch index made a big jump from 3.9 on average across samples to 6.9 this week. Brix level is 12.2.

The story, when you add up all these maturity indices, is that Gala is quickly moving out of a mid-term controlled atmosphere (CA) window for any fruits not treated with harvest management materials.

McIntosh were not sampled this week due to our blocks being harvested. There are some Macs still hanging and they will move quickly into an over mature range if not treated with harvest management tools. Fruit drop will become a concern with the very hot weather on tap.   

Honeycrisp maturity is indicating over-mature fruits for the most part. There are less mature fruits still present, waiting for the second pick, but this variety has moved through its maturity very quickly this season. Watch your sites carefully and test for firmness and starch to monitor maturity block by block.

Firmness readings in Honeycrisp are still very good at 17.8 pounds compare to 18.1 pounds last week. Starch readings are now all in the 7 to 8 range. Brix level declined a bit to 12.3—perhaps due to sampling from second pick fruits.

Bitter pit still seems to be low overall, but we do see a bit more this week compared to last week’s sampling. There is also an increase amount of lenticel rot now being found—it has increased noticeably compared to last week. My colleagues in southeast and southwest Michigan are also reporting more lenticel rot in Honeycrisp this week too.  

Empire are slowly moving forward in their maturity as is typical for this variety, and they are now just entering the long-term CA window in the Grand Rapids area. Color is improved to 80.3 percent, up from 68 percent last week. The background color has changed from last week’s 3s to more 1s and 2s this week. Fruit firmness is excellent at 19.6 pounds this week. The starch index readings were all 4s this week compared to all 2s last week. Brix have improved from 12.8 last week to 13.4 this week. They eat much better this week compared to last.

The predicted peak harvest date for Empire is Sept. 25 and that date is looking to be a couple of days late, so get Empires off as you have time.

Jonathan harvest is ongoing in some blocks as required by buyers. The block we have been sampling has been harvested, so we have no data for this week, but I would imagine data points would be very similar to the Jonagold readings listed below. Sept. 27 is the predicted harvest data, which might be a little on the late side. Keep an eye on your Jonathans, they can be harvested at any time. We are seeing and hearing of increased bleeding of red color in the very red strains of Jonathans.

Jonagold has moved very quickly forward in maturity—the starch readings jumped this week. Internal ethylene production in our Jonagold samples is now over 0.2 ppm in 35 percent of fruits sampled. Red color is up only slightly from 36 percent last week to 39 percent this week. The background color averaged 2.6 with a range of 2 to 5. Fruit firmness is still good to excellent at 17.9 pounds, but has declined from last week’s 21.1 pounds.

Starch index readings made a big movement in Jonagold from an average of 3.2 last week to 6.7 this week. It was a bit surprising to see that big leap forward. Brix level is up slightly from 12.9 last week to 13.1 this week.

The predicted harvest date for Jonagold was Sept. 27 for peak harvest. That date is looking a little too late for what should be peak harvest. If you are considering long-term storage for Jonagold, you should get started on them soon.

Golden Delicious have a predicted harvest date of Oct. 1 for the general Grand Rapids area. Our samples this week showed some changes in the internal ethylene development and starch readings. Golden Delicious are overall immature, but they are very near to the timing for first harvest for long-term storage. There are now 40 percent of fruits with internal ethylene over the climacteric of 0.2 ppm—last week there were zero. They are very green with a background color of 4.3 on average, but we are seeing a few more 3s this week where all fruits were 4s and 5s the last two weeks.

Pressure is good to excellent at 17.3 pounds and it is declined from last week’s 22 pounds. Starch clearing made a leap forward with an average this week of 5.4 compared to last week’s 2.6. Brix are good, but not excellent at 12.5—not typical for Golden Delicious that tend to run lower in brix than other Michigan apple varieties.

The long-term CA window is just starting to crack open for Golden Delicious, and if you have blocks that develop on the early side, you could get started with harvest when time and help allows. The predicted harvest date of Oct. 1 appears to be on the late side when looking at the maturity indices for Golden Delicious.

Cortland is immature with an average starch reading of 1.8 and a background color of 3.4. Brix are really good for Cortland at 12.9. Cortland harvest is usually between Jonagold and Red Delicious and they need some time yet to mature. You will get to them when time and help allows fitting them in.

It seems like every year, we get busy with all the other mid-season varieties and we forget to start sampling Early Fuji on time. We are probably two weeks late to look at them as our first sample this week shows them to be right in the range for early harvest with a starch of 5.6 and a background color of 1.9. Brix are excellent at 14.8.

There was little to no water core in the samples we looked at; Early Fuji do tend to have less water core than late Fuji. This variety is mainly for fresh sales and they do eat very nice right now and should be harvested sooner rather than later.

Next week, we will add all the later season varieties to our sampling—Red Delicious, Ida Red, Rome and Fuji—to start looking at maturity development over time.

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