MSU Extension Apples

This is the 10th 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 October! This week in the Grand Rapids, Michigan, area, harvest of mid and late-season varieties continues, with most untreated fruit maturing very close to the predicted harvest dates. Testing this week included Empire, Jonathan, Jonagold, Golden Delicious, Red Delicious, Aztec Fuji, Ambrosia, Idared, Granny Smith, Rome, Evercrisp and Braeburn. Overall, fruit size is very good, crop load is excellent, and red color is developing very well. Sugars and pressures have generally been a bit low this season compared to past seasons, likely due to the significant rainfall leading up to harvest. Crop and fruit size has been exceptional, as predicted.

Weather conditions in the Grand Rapids area continued to be very cool, with high temperatures in the 60s (degrees Fahrenheit) most of this week. Low temperatures were near 40 most nights this week, and in many places dropping into the 30s on several mornings. It has been very dry in the region, with the last significant rainfall on Monday and Tuesday last week and more than 0.2 inch of accumulation recorded at most weather stations.

Expect cool conditions to continue, with a colder trend Thursday through the weekend. Very cold conditions are especially likely over Friday and Saturday mornings. Highs may only reach into the 50s. A chance of precipitation is possible on Thursday afternoon with less than 0.1 inch of accumulation expected.

Chilling conditions. Temperatures fell to the low 40s and upper 30s in many places. These temperatures have the potential to cause chilling injury in sensitive varieties. Temperatures for potential Honeycrisp chilling injury begin around 37 and are likely at 34. Other sensitive varieties include Jonathan, McIntosh and Empire.

Chilling potential is based on research conducted by MSU’s Randy Beaudry, summarized in this article about cool, fall nights and challenges for fruit storability. In general, Beaudry’s research found that fruit that sustained two nights of low temperatures experienced more chilling injury. This suggests that “low field temperatures slightly enhanced fruit sensitivity to chilling in storage.” In addition, “conditioning reduced chilling, ReTain increased the incidence of chilling, storage at 32 F (compared to 37 F) increased chilling injury, and conditioning increased bitter pit incidence.” Lower lying blocks, where cool air pools are at higher risk. Forecasts indicate there is the potential for chilling temperatures again this week, with the lowest temperatures predicted for the weekend.

Avoid handling frozen fruit. As a reminder, frozen and wet fruit will bruise more easily during harvest and transport. If fruit is lightly frozen, it will thaw much better on trees. Cut fruit to make sure they are thawed throughout, and not just the frost from the surface of the fruit. Do not leave bins in the orchard if freezing temperatures are expected.

How to read maturity tables

***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.***

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 past peak harvest for untreated fruit, but treated fruit continues to be picked this week. Sugar was slightly improved this week and firmness is still good in most fruit. Starch clearing is averaging 4-6. Ethylene was being produced in a significant amount in just under half of fruit tested this week.

Jonathan (predicted harvest date: Sept. 27)

This variety is mature or past mature in untreated blocks this week. Red color is very good, as expected for this variety. A little more than half of fruit tested were producing a significant amount of ethylene. Sugars improved considerably this week. Pressure remained fairly stable this week, with averages at approximately 14 lbs. Recommended pressures are 14-16 depending on the intended storage time. Starch was more advanced, with averages of approximately 6. In two of the locations tested this week fruit we observed bleeding in a couple of fruit.

Jonagold (predicted harvest date: Sept. 27)

This variety is mature or nearly mature this week. Most samples collected this week were treated with ReTain—very few Jonagolds are untreated in the area this year. Red color development improved this week, and background color was much less green. Ethylene was being produced in significant amounts samples taken from two locations, one of which was NOT treated with ReTain. Sugars are much better this week and flavor is also very good. Pressure was a little low in tested fruit; recommended pressure for this variety is 15-17, depending on the intended storage time. Starch clearing was considerably advanced this week with averages between 6.2-6.8.

Red Delicious (predicted harvest date: Oct. 1)

This variety is nearly mature in most locations. Red color is very good, background color is a bit lighter this week. None of the fruit tested were producing significant amounts of ethylene. Starch clearing is a bit more advanced, with averages between 2.6 and 3.2. Sugars are still a bit low. Overall pressure is still good, aside from a couple of softer fruit. Recommended pressures are 16-18 depending on the intended storage time.

Golden Delicious (predicted harvest date: Oct. 3)

This variety is still ready for harvest in most locations where fruit are not treated. Fruit is much more yellow this week, and in most locations a red cheek is present on a considerable amount of fruit. Ethylene was only being produced in about half of fruit tested this week this week. Starch clearing was more advanced, and averaged between 3.8 and 6.5 this week. 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, averaging from 15.5-16.5. Recommended pressures for this variety are 15-17 depending on the intended storage time. Sugars improved considerably in most locations this week. Varietal flavor is very good in this variety. Moldy core was observed in a couple of fruit from one location this week.

Aztec Fuji

This variety is nearly mature this week for long term storage. While it usually is often left later in the season, mostly for color, this variety often is mature soon after Red Delicious. Red color was much better this week, and background color was less green. Overall fruit is still very firm, with samples averaging 17-18 lbs. Sugars were still a bit low, but varietal flavor is beginning to develop. Starch has already begun clearing, with averages between 3.5-5.0 this week. Fruit is likely to mature earlier than our predicted harvest date.

Idared (predicted harvest date: Oct. 6)

Overall, fruit is still fairly immature. Red color development is very good in most locations. Pressure was similar to last week, with samples averaging 14.5-16.1 lbs. Sugars improved, but are still a bit low, although this is a more acidic variety. Fruit is still very starchy, with averages between 1.6-3.2 this week. A little less than half of fruit tested this week were producing significant amounts of ethylene.

Ambrosia

This variety is mature and being harvested this week and last. It should be harvested close to Empire timing. Red color development is much better, and background color is beginning to change from green to a lighter green-yellow. Fruit is still fairly firm, with samples averaging near 17 lbs. Sugars are a bit better than last week, and varietal flavor is good. Starch clearing is continuing gradually, with averages for all samples averaging 4.1-4.6 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.

Detailed recommendations for Ambrosia harvest have been made by Washington State University and ONFruit. Both indicate that it is important to harvest this variety before the background color changes to yellow, if it is intended for long term storage. Starch clearing may not be the best indicator of maturity. Instead, recommendations are to use DA (Delta Absorbance) as an indicator. For long term storage, a range of 0.7-0.5 is recommended. In two locations we tested this week, fruit was between 0.66-0.55, indicating it is ready to be harvested.

Granny Smith

Fruit is beginning to show signs of maturity but is still very green. Fruit is still very firm, with samples averaging around 18-19 lbs. Sugars are still low and fruit tastes extremely sour. Starch clearing is progressing slowing, with averages for all samples near 2.3 this week. None of the fruit tested this week were producing significant amounts of ethylene.

Law Rome (predicted harvest date: Oct 11)

Overall, fruit is still a bit immature. Red color is very good. Fruit is still very firm, with samples averaging over 20 lbs. Sugars were a bit better in tested fruit, but still a bit low. Starch clearing is progressing slowly, with averages for all samples between 2.0-3.0 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, but we did not observe this in any samples this week.

Evercrisp

Overall, fruit is very immature. Red color just beginning and background color is still very green. Fruit is still very firm, with samples averaging over 20 lbs. Sugars are still low. Starch clearing is just beginning with averages near 2.0 this week. None of the fruit tested this week were producing significant amounts of ethylene.

Braeburn

We tested this variety for the first time this week. Overall, fruit is very immature. Red color just beginning and background color is still very green. Fruit is still very firm, with samples averaging over 19lbs. Sugars are still low. Starch clearing is just beginning with averages near 2.0 this week. None of the fruit tested this week were producing significant amounts of ethylene.

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.