MSU Extension Apples

General comments

Week two of our Grand Rapids area apple maturity sampling has a few surprises in store. Early ripening varieties such as Gala and Honeycrisp are moving very quickly through their maturity parameters. Mid-season varieties seem to be taking on a more normal pace at this time and another week of sampling will really help determine how quickly those varieties are going to move.

In the Grand Rapids area, apple maturity seems to be running close to our 2018 predicted apple harvest dates with continued indication from early varieties that peak maturity might be advanced by three to five days from these dates. Our predicted harvest dates are for peak harvest, so some fruits might be ready ahead or behind these dates as we move through maturity. When we sample apple varieties, we try our best to collect random samples from blocks untreated with harvest management products.

There are some strange spots on apples here and there. At this time, we haven’t identified the cause and it could be one of several problems – lenticel injury with rot moving in, the early stages of San Jose scale infestations, bitter pit or perhaps brown marmorated stink bug.

If you are seeing anything you would like further investigation on, please let me know and I’ll come get a sample. Pictures sent via email or text are also great (irisha@msu.edu or 616-490-1079).

Notes on the upcoming hot weather

In 2017, there was extreme heat in late September. We are in for a bit of a warm spell in the next few days, but nothing like the over 90 degrees Fahrenheit we had in 2017. Nonetheless, warm weather does bring special concerns during harvest, so be ready for high CO₂ levels in rooms after they are closed due to increased fruit respiration. Be sure you have that fruit cooled down well before sealing everything up. Adding a half skid of lime in the room will help as well. There can also be issues when applying 1-MCP in the room with warm fruit. For instance, Golden Delicious will get a “ghosting” on the surface if 1-MCP is used on warm fruit.

Very warm temperatures in September could lead to higher incidence of superficial (storage) scald in susceptible varieties, which we did see quite commonly in 2017. Treat fruit rapidly after harvest with DPA or 1-MCP to minimize risk.

Apple variety sampling results

Color is very good to near excellent on most Gala strains this year and continues to improve. The past week of cooler temperatures helped tremendously for color development. Size is also good to very good, but a little on the small size overall. Gala have seemed to move quickly in their maturity, which is very common when there is hot and dry weather in July and August. Please watch your individual blocks very carefully, even if you have used harvest management applications.

Our predicted harvest date for Gala for peak harvest is Sept. 10 and a fair few have gone into bins in the last week. We normally like to recommend a starch index of 3 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. Gala is in the prime window for long-term CA storage this week. All untreated fruits sampled this week are over the internal ethylene climacteric of 0.2 ppm—fruits treated with AVG have lower ethylene in general.

Red color is much improved at 92 percent on average compared to 68 percent last week. Background color is about the same and quite low, indicating maturity. Firmness is still excellent at 19.2 pounds on average this week, but the range of pressure is tightening up a bit. Starch index is up to 3.7 this week compared to 2.8 last week. Starch readings are quite variable this year, so if you are checking your own fruit, make sure you have at least a 10 apple sample (20 is better) to get the best picture of what the average starch is. Brix are very good at 13.3, up from 12.8 last week.

McIntosh continue to be a bit slower in expected maturity for 2018 with very low internal ethylene. Color is greatly improved from 69 percent red color last week to 85 percent this week. Internal ethylene is still very low. Background color has improved from 4.4 last week to 2.3 this week. Firmness is excellent at 16.8 pounds. The starch index has moved upward slightly to 3.5 on average compared to 2.7 last week and brix are at 13 this week compared to 11.9 last week.

The predicted harvest date for peak McIntosh harvest is Sept. 14, which might be a day or two on the late side. Be watchful in blocks with a heavy fruit set as drop could occur from fruits pushing themselves off as they grow. The warmer weather coming later this week might move Macs forward, and you should watch your blocks closely.

As I stated last week, Honeycrisp is moving very quickly toward maturity—much faster than anticipated. Watch your sites closely. Firmness readings are good but still not excellent (likely from all the recent rains). Starch readings continue to be all over the chart, which isn’t unusual for Honeycrisp. Starch clearing is slightly higher that than last week, and much higher than this stage for 2017.

Brix level has improved from 12.7 las week to 12 this week. Many Honeycrisp fruits eat very well, and they are very juicy from the heavy rainfall. This also concerns me as to the storability of the first picking—fresh sales are recommended. Later pickings should store better.

There is a bit of bitter pit starting to show up on blocks with a light crop load. Bitter rot is also present and not surprisingly given all the rain recently. Our predicted harvest date of Sept. 18 is starting to look a little too late for peak harvest of many Honeycrisp sites in the Grand Rapids area.

We sampled Empire for the first time in 2018. All indications are that Empire are immature. Our predicted date for Empire peak harvest in the Grand Rapids area is Sept. 24 and they will need another 10 to 14 days to get there for the various maturity indices. No fruits have internal ethylene over the 0.2 ppm climacteric, but there is some internal ethylene starting to develop.

Red color averages 53 percent with a wide range from 15 to 80 percent. Background color is lower than expected at 2.4 on average. Firmness is excellent at 17 pounds. Starch index is low as expected at 1.8. Brix are on the low side as well at 11.8 on average.

Jonagold was also sampled for the first week. The predicted harvest date for Jonagold and Jonathan is Sept. 26 and they will need those two weeks to move forward in maturity. There is some internal ethylene present, with only 10 percent of fruits being over the 0.2 ppm level.

Red color is not very good at 31.5 percent, and more time and cool weather conditions are needed to develop anthocyanins. Background color is a bit advanced of expected levels as with Empire which could be a factor related to the person doing the evaluation.

Firmness is very good in Jonagold as expected with an average of 17 pounds. There are a few fruits sampled with quite low pressure which could be a factor of all the recent rain. Starch levels are very low at 1.8. Brix levels are good at 11.8 on average and should only improve in the next two weeks.

This was the first week for Jonathan sampling as well. Ruby Jon was our sample cultivar, so the red color of 97 percent should be no surprise. The predicted harvest date for peak Jonathan harvest is estimated to be Sept. 26 and while some early taffy apple harvest is happening, this date is shaping up to be accurate. Processors will want fruit when they want them so follow their lead.

We sampled Golden Delicious for the first time in 2018. They are immature at this time. The predicted harvest date for peak harvest in the Grand Rapids area is Sept. 28.

Cortland is immature with an average starch reading of 1 and a background color of 2.3. Brix are rather good for Cortland at 13. Harvest of Cortland is usually between Jonagold and Red Delicious and they need some time yet to mature.

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 most likely won’t sample them this year in time to give good guidance. They do eat very nicely right now and should be harvested sooner rather than later.

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 = measured with a Güss Fruit Texture Analyzer; range is of all fruits tested.
• Starch: 1 = all starch, 8 = No starch; range is of all fruits tested. Using Cornell Starch Iodine Index Chart.
• Brix = % sugar measured with Atago PAL-1 Pocket Refractometer

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