MSU Extension

General comments

This is the second Michigan State University Extension apple maturity report from the Grand Rapids, Michigan, area fruit team. Now that we’ve had a bit of sampling under our belts, we feel that the predicted apple maturity dates seem to be near the target for the peak of harvest for early ripening varieties or about 4 or 5 days ahead of an average date. Due to the very long bloom period back in May, later varieties are predicted to be more normal in their harvest dates this year – time will tell if that is correct.

Fruit color has greatly improved in the last few weeks. It’s been a few years since we have had nice coloring weather in Michigan. Size has been average if you put all fruits together and make an average. However, there is great variability in fruit size across the region – mostly likely due to poor pollination and fertilization weather for that month-long bloom period this spring.

Growers are starting to go after Honeycrisp where color is adequate. Gala and McIntosh are also being harvested. An interesting thing about Gala and Macs: in warm summers, Gala will ripen first; in cooler summers, Macs will be ahead of Galas. This year is different in that it’s been moderate, neither too warm nor too cold, but a mix of each depending on the week. So, we are seeing in our maturity indices that Gala and McIntosh are likely to ripen together in 2017. Just when you think you know something….

We use many measurements or indices to determine apple maturity. While this might seem confusing, the real reason is that we really don’t trust any single measurement alone. Internal ethylene is probably the most reliable measurement, but not easy for everyone to measure without some very expensive equipment. Internal ethylene ultimately tells the rate of ripening – no other measurement does this. Without ethylene, there is no ripening. Some years are high ethylene years and others are low ethylene years. 2017 seems to be on the low side, but it’s been changing quickly as the predicted harvest date nears. Starch is the easiest to measure and gives an indication of the overall fruit development, but not necessarily ripening. We look at fruit firmness, red color, background color and now the DA meter readings. All these measurements add up to tell the apple maturity story. Our MSU Apple Maturity team hopes you find this report useful.

Variety sampling results

Gala color is still very good to excellent on most strains this year and hasn’t improved much from last week’s samples. Size is good to very good, depending on crop load. Gala are just coming in to the window for long-term CA storage where no harvest management applications were used. Our predicted harvest date for Gala for long-term CA storage was Sept. 5 and it’s looking like this date is accurate for early harvest, but perhaps a little early for the peak of harvest. A starch index of 3 is recommended for long-term storage of Gala, but if color and size are where you need them, you could pick for long-term CA storage at a starch index of 2.

Our sampling this week shows a jump in starch readings from mostly 1’s last week to an average of 3 this week. Nearly all fruits now are over the 0.2 ppm internal ethylene mark, so ripening cannot be held back now in untreated Galas. Watch your blocks carefully.

McIntosh have made a step forward in maturity with a few fruits (16%) now over the 0.2 ppm internal ethylene level. Color is very good on the redder strains. Our samples show a background color averaging near 2, which also indicates Macs are ready for long-term CA storage. Pressure readings are 15.7 pounds which is a slight reduction from last week’s 16.5 pounds. Brix reading has improved slightly from 12.4 last week to 12.7 this week – quite typical for Macs.  

I mentioned in last week’s report that Honeycrisp were moving rather quickly toward maturity and that still holds true for this week. Some initial harvest has begun in blocks with no harvest management applications on. Our predicted harvest date is Sept. 15 for the Grand Rapids area peak Honeycrisp harvest. Perhaps this is a little on the late side – maybe 2 or 3 days – it’s just a guide. We sampled over 45 Honeycrisp blocks in the last week and the numbers are greatly variable from block to block and even apple to apple in each sample. Such is the way of Honeycrisp. If you are considering storage for Honeycrisp (refrigerated or controlled atmosphere), the use of 1-MCP would be highly recommended for the 2017 harvest as they seem to be moving rather quickly through the various stages of maturity and ripeness.

Watch your sites carefully and test for firmness and starch to monitor maturity block by block. Firmness readings are still very good to excellent at an average of 15.4 pounds, down from last week’s 17.5 pounds. Starch readings continue to be variable as is typical for Honeycrisp, averaging 5.9 with a range from 3 to 8 on the Cornell starch index chart. Brix level improved from 12.6 last week to 13.1 this week. Honeycrisp are eating very nicely if you find one with a high starch index reading.

Bitter pit seems to be less in Honeycrisp in 2017 than the past two years. In fact, I’ve noticed, and many have told me they’ve noticed, some bitter pit starting to show back in late July or early August. I thought we were in for another bad year, but it seems to have not progressed very much. Many reasons could explain this – drier summer, less vegetative growth calling for nutrients; we have learned to back off on our general fertility program for Honeycrisp; cooler weather might have something to do with it; etc., etc. I think it basically tells us that we still have a lot to learn about bitter pit.

Empire were added to our sampling this week. All maturity indices say they are still immature. We will continue to monitor.

Jonathan were also added to our sampling this week and they, too, are immature according to maturity indices. There have been some Jonathans picked for taffy apples. The predicted harvest date for Jonathan in Grand Rapids is Sept. 27 for peak harvest. A few fruits are starting to show some internal ethylene and there is a bit of starch clearing happening with an average reading of 2.6.

We sampled Jonagold for the first time this week also. Their numbers are very similar to Jonathan as usual and Jonagold are immature at this time as well. Our predicted harvest date for Jonagold is Sept. 27 and they will likely need another two weeks to start moving forward in their maturity.

Golden Delicious were included in our sampling this week for the first time. There were no fruits with internal ethylene over the climacteric of 0.2 ppm. They are very green with a background color of 4.5 on average. Pressure is very good at 16.8 pounds. Very little starch clearing with an average starch index of 1.3 across the sample. Brix are pretty good at 12.2. While we praise the great coloring weather for most varieties, in Golden Delicious, the cool nights and sunny days are adding a little pink cheek.

Next week we will continue sampling all the varieties listed above and add a few more.