MSU Extension Apples

This is the eighth maturity apple maturity report for 2022. Reports are sent out every week (usually on Wednesdays), following the Michigan State University Extension fruit team apple maturity calls on Wednesday morning. 

Happy (almost) Fall! The Autumn Equinox is tomorrow, Sept. 22, with the promise of cool weather around the corner. This week in the Grand Rapids area, harvest of Gala, Honeycrisp, and McIntosh continues. A large part of the crop has been picked; second and third picks are underway, as well as fruit treated with ReTain and Harvista. Testing this week included Empire, Jonathan, Jonagold, Golden Delicious, Red Delicious, Aztec Fuji, Ambrosia, Idared, Granny Smith, and Rome. Overall this week, fruit size is very good, crop load is excellent, and red color is developing very well.

Weather conditions in the Grand Rapids area this week were above average and mostly dry. Temperatures were near 80 Fahrenheit most of the week and weekend, and lows in the mid-60s F. Rainfall was minimal, with less than 0.25 inches in most places on Sunday, and less than 0.1 inches on Tuesday, aside from heavy rainfall in isolate locations. As of Sept. 19, the Michigan State University Sparta Enviroweather station has accumulated 3733.6 Degree Days Base 42 F (DD42). This is above average, which is 3543.8 DD42, and approximately ten days ahead of normal. The map below shows DD base 50 accumulation compared with normal values, taken from the Enviroweather website. However, expect an abrupt change this week as a cool front moves into the area. High temperatures are expected to be in the mid-60s F with overnight lows in 40s F. 

***The majority of fruit were sampled from untreated blocks (no ReTain or Harvista applied). However, a couple of samples this week included fruit that were treated, as it is becoming more difficult to find untreated fruit.*** 

How to read maturity tables

Each week, we test apple varieties that are nearing maturity in the Grand Rapids. We are reporting average values for several samples for each variety. Maximum and minimum values are included for the highest and lowest individual fruits evaluated for each, to give a full spectrum of the maturity. All samples included in the reports have been untreated with ReTain or Harvista, unless otherwise noted.

• Predicted apple harvest dates for 2022 from MSU
• More information on harvest management tools and timings can be found in this article.
• Guidelines from MSU to check for apple maturity in your own orchard, including specific pressure and starch recommendations by variety.
• Predicting apple maturity and starch chart from Cornell University
• Starch chart for Honeycrisp Apples developed by Washington State University.

Empire (predicted harvest date: Sept. 25)

Fruit is developing very nice color and size. Fruit in most locations is ready for long term storage, fruit that is intended for direct market or shorter storage needs a bit more time. Starch clearing is continuing gradually, with averages between 2.5-3 this week. Sugars are still a little lower than preferred. Only fruit from one sample/location were producing significant ethylene. Pressures were beginning to decrease, although some fruit were still quite hard. This variety is nearly mature for storage, but needs a bit more time for shorter storage or direct market, very close to our predicted harvest date. 

Jonathan (predicted harvest date: Sept. 27)

This variety showed more signs of maturity this week. Red color is very good, as expected for this variety, and background was a bit less green. Again, this week, a fruit collected were producing a significant amount of ethylene. Sugars improved just a bit, but are still lower than ideal. Pressure was still very good overall, but a few fruit were very soft. Recommended pressures are 14-16 depending on the intended storage time. Fruit is nearly ready for long term storage. In one of the locations tested this week fruit we observed bleeding in a couple of fruit. In another location approximately 30% of fruit had mild water core.

Jonagold (predicted harvest date: Sept. 27)

This variety is still immature but showing more signs of maturity. Samples collected this week were treated with ReTain—very few Jonagolds are untreated in the area this year. Red color development improved this week, but background is still very green. Ethylene was only being produced in significant amounts in two fruit that were tested. Sugars are a bit better, but still lower than ideal. Pressure was still very good in tested fruit; recommended pressure for this variety is 15-17, depending on the intended storage time. Starch clearing was more advanced this week with averages between 3.5 and 4.5. Fruit needs a bit more time before harvest and likely will be mature at approximately the predicted harvest date. In one sample/location, a couple of the fruit had watercore this week. 

Red Delicious (predicted harvest date: Oct. 1)

This variety is still immature. Red color is good in most locations, but background color is still fairly green. Only one of the fruit tested this week was producing significant amount of ethylene. Starch clearing is still beginning, with averages between 1.5 and 2.5. Sugars are still very low. Overall pressure is still very good, aside from a couple of softer fruit. Recommended pressures are 16-18 depending on the intended storage time. This variety is beginning to mature, but still needs week or two.

Gold Delicious (predicted harvest date: Oct. 3)

This variety is still immature, but showing more signs of maturity. Background color is still fairly green, but slightly lighter this week. Just a touch of pink is present on the blush side of a few fruit, but not most of the fruit on trees. Ethylene was not being produced in any of the fruit sampled this week. Starch clearing is moving gradually, and averaged between 2.5 and 3.8 this week, with a couple of outlier fruit that were more advanced. The pattern in this variety can also be a bit different than the traditional McIntosh starch staining, with flesh clearing before the entire core is clear. Overall, pressures are still very good. Recommended pressures for this variety are 15-17 depending on the intended storage time. Sugars are improving, but still a bit low as well. 

Aztec Fuji (predicted harvest date: Oct. 21) 

We sampled this variety for the first time this week. While it usually is often left later in the season, mostly for color, this variety often is mature soon after Red Delicious. Fruit is still very green, with red color development beginning. Overall fruit is still very firm, with samples averaging 18-19 lbs. Sugars are still a bit lower than desirable. Starch has already begun clearing, with averages between 2.7 and 3.0 this week (photo). Fruit is likely to mature earlier than our predicted harvest date. 

Idared (predicted harvest date: Oct. 6)

We sampled this variety for the first time this week. Overall, fruit is still very green, with red color development variable depending on location. Fruit is still fairly firm, with samples averaging 14-17 lbs. Sugars are still a bit low, although this is a more acidic variety. Starch clearing is just beginning, with averages for all samples near 1.5 this week. 

Ambrosia

We sampled this variety for the second time this week. Fruit is beginning to show signs of maturity. Red color development still low, but background color is beginning to change from green to a lighter green-yellow. Fruit is still fairly firm, with samples averaging 17-18 lbs. Sugars are still a bit low, but a bit better than last week. Starch clearing is continuing gradually, with averages for all samples near 2.1 this week. A few fruit were producing significant amounts of ethylene this week, but this seems to be a variety that produces high amounts of ethylene before harvest, based on our work last year and this year so far. 

Granny Smith

We sampled this variety for the first time this week. Overall, fruit is still very green. Fruit is still very firm, with samples averaging 18-20 lbs. Sugars are still low, and fruit tastes extremely sour. Starch clearing is just beginning, with averages for all samples near 2.0 this week. None of the fruit tested this week were producing significant amounts of ethylene.

Law Rome (predicted harvest date: Oct. 11) 

We sampled this variety for the first time this week. Overall, fruit is still very immature. Red color is developing nicely, but background color is still green. Fruit is still very firm, with samples averaging 18-20 lbs. Sugars are still low. Starch clearing is just beginning, with averages for all samples near 1.5-2.0 this week. None of the fruit tested this week were producing significant amounts of ethylene. This variety is susceptible to red color bleeding from the skin into the flesh, which we observed in one prematurely ripe fruit this week (photo). 

Apple maturity sampling parameters

• Ethylene (% 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. Indicates surface area covered in red and intensity of red color.
• 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.
• Starch For Honeycrisp: will typically be rated using the standard Cornell SPI scale (1-8). However, a separate starch chart for Honeycrisp Apples developed by Washington State University (scale 1-6) also exists.
• 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.