MSU Extension Apples

This is the 11th 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. 

This week in the Grand Rapids area, harvest of mid-season varieties, including Red and Golden Delicious, is winding down and later season varieties are beginning. Testing this week included Jonathan, Jonagold, Golden Delicious, Red Delicious, Aztec Fuji, 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 Farheninet most of this week. Low temperatures were in the upper 30s F most nights this week. Most of the week was very dry, aside from rain overnight Tuesday into Wednesday with accumulation of about 0.1-0.2 inches in the Sparta area, and a bit more farther north (0.4-0.5 inches). Rain is expected to continue over Wednesday, with possible accumulation of .5 inch or more. Overcast skies and light showers are likely for the remainder of the week. Expect cool conditions to continue, with a colder trend Thursday through the weekend. High temperatures are expected to be in the low-50s F to mid-40s F through the middle of next week. Forecasted low temperatures will be in the mid- to upper-30s F most days, and in some locations are below freezing. 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 F and upper 30s F in many places over the past two weeks, and temperatures are expected to be cold again this week. These temperatures have the potential to cause chilling injury in sensitive varieties. Temperatures for potential Honeycrisp chilling injury begin around 37 F and are likely at 34 F. Other sensitive varieties include Jonathan, McIntosh, and Empire. 

Chilling potential is based on research conducted by 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.  

This article from PSU addresses concerns about lower temperatures. Fruit exposed to sustained low temperatures will be more affected, while fruit exposed to marginal temperatures for a night or two are likely to have injury. The work done by Jim Schupp found that fruit exposed to four hours or more of 28 F or lower are more likely to develop cold injury. Fruit exposed to marginal temperatures for only a night or two may recover, but will not be good candidates for long term storage as fruit may soften rapidly. Frozen fruit may also sustain flesh browning. “Fruit that were fatally frozen will exhibit flesh browning after thawing once the temperature has risen far enough for oxidation to take place. This browning can appear at the skin surface or below, and generally takes ~24 hours to appear, longer if temperatures remain cold. After the apples have warmed enough to exhibit flesh browning, cut fruit open and inspect them. If browning appears, the fruit is obviously unfit for use.” https://extension.psu.edu/fruit-harvest-handling-of-frozen-apples  

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.

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. All tested were producing a significant amount of ethylene. Pressure, starch and sugar levels remained fairly stable this week, with averages at approximately 14 lbs. Recommended pressures are 14-16 depending on the intended storage time. In two of the locations tested this week fruit we observed bleeding in a couple of fruit (approximately 15-20% of fruit tested).

Jonagold (predicted harvest date: Sept. 27)

This variety is past mature if untreated. Most samples collected this week were treated with ReTain—very few Jonagolds are untreated in the area this year—and these samples were past mature or are mature this week. Color and size are excellent. Ethylene was being produced in significant amounts in a majority of fruit tested. Recommended pressure for this variety is 15-17, depending on the intended storage time.

Red Delicious (predicted harvest date: Oct. 1)

This variety is being picked now in most locations. Color and size are very good. Fruit from one location (not treated with ReTain or Harvista) were producing significant amounts of ethylene (40% of fruit). Starch clearing is variable, ranging from an average of 2.1 to 3.1 depending on the block. Sugars are still a bit low. Overall pressure is still good, with averages of 16 or greater at each location tested, aside from a couple of softer fruit. Recommended pressures are 16-18 depending on the intended storage time. Moldy core and watercore were observed in 10-15% of fruit evaluated. 

Golden Delicious (predicted harvest date: Oct. 3)

This variety is mature or overmature 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 a majority of fruit at most locations (one location had no ethylene production and was treated with ReTain). Starch clearing was considerably more advanced, and averaged between 4-8. 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, pressure was a bit lower, ranging from 13.6-17.4 on average. Recommended pressures for this variety are 15-17 depending on the intended storage time. 

Aztec Fuji

This variety is mature or nearly mature this week. While it usually is often left later in the season, mostly for color, this variety often is mature soon after Red Delicious. Red color is very good in most locations. Pressures decreased a bit this week, with samples averaging 16.7-18.6 lbs. Sugars are a bit better this week, though lower than we see in some years for this high-sugar variety. Flavor of fruit was good in fruit we tested. Starch clearing indicates fruit is ready for storage, with averages between 4 and 4.5, depending on location.

Idared (predicted harvest date: Oct. 6)

Overall, fruit is nearly mature, and will be ready for harvest next week in most places. In untreated blocks, fruit may be ready for long term storage by the end of this week. Red color development is very good in most locations. Pressure was similar to last week, with samples averaging 14.3-15.4 lbs. Sugars are still a bit low, although this is a more acidic variety. Starch clearing was more advanced, with averages between 2.2-4.1 this week. A little less than half of fruit tested this week were producing significant amounts of ethylene. 

Granny Smith

Fruit is showing more signs of maturity and will be ready for harvest in many places next week. Fruit is still very firm, with samples averaging around 18-18.5 lbs. Sugars were a bit better, but fruit still tastes very sour. Starch clearing is progressing slowing, with averages for all samples near 2.5 this week. None of the fruit tested this week were producing significant amounts of ethylene.

Law Rome (predicted harvest date: Oct. 11)

Fruit is being picked this week in many locations. Red color is very good. Firmness is still very good, with samples averaging over 20lbs. Sugars were a bit better in tested fruit. Starch clearing was considerably more advanced, with averages for all samples between 3.4-5.0 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

Fruit is beginning to mature and may be ready for harvest in some locations next week. Red color is good in most places. We have noticed that younger trees or trees with poor light tend to have poor or less bright color. Fruit is still very firm, with samples averaging over 20lbs. Sugars are much better this week with averages of over 13 in all locations tested. Starch clearing is more advanced, between 2.5-4.1 in fruit tested. A few fruit were producing significant amounts of ethylene. Recommendations from PSU are to harvest for long term storage at 4-6 and for direct market at 6-7 starch index. This variety has some sensitivity to CO2 injury in longer storage, which may cause internal browning.

Braeburn

Overall, fruit is still immature. Red color is improving and background color is still very green. Fruit was slightly softer, with samples averaging 18 lbs. Sugars are still low. Starch clearing is just beginning with averages between 2-4. 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.