MSU Extension Apples

This is our weekly southwest region apple maturity report. Reports are sent out on Wednesdays, following the Michigan State University Extension fruit team apple maturity calls on Wednesday morning. 

Notes modified from report by Anna Wallis, Extension Apple Specialist, Grand Rapids, MI 

Chilling conditions

Temperatures in the low 40s Fahrenheit and upper 30s F during harvest season 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 Dr. Randy Beaudry, summarized in this article about cool, fall nights and challenges for fruit storability. In general, Dr. Beaudry’s research found that fruit that sustained 2 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.  

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.

More information sources: 

• 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.

Additional notes

Pristine plus Captan or Merivon plus Captan would be the best preharvest materials to minimize storage rot problems.

Distinguishing between stink bug and bitter pit damage on apples is not always easy. Articles from Cornell and Michigan State University can help.

The Michigan Department of Agriculture and Rural Development (MDARD) has a Pesticide Applicator Credit Report on MDARD’s website under recent additions section. Michigan pesticide applicators can look up the number of credits they have accumulated.

How to read the maturity tables

We test apple varieties that are nearing maturity in the southwest Michigan area, with focus on Berrien County. We are reporting average values for firmness, starch index and brix for several samples for each variety. Maximum and minimum values are included for the highest and lowest average for individual orchards. Most fruit were sampled from untreated blocks (no ReTain or Harvista applied). However, some of the data shown here included fruit that were treated with ReTain.

Jonagold & Empire 

No new samples this week. These varieties are fully mature in the southwest Michigan region.

Fuji (Main season)

Starch conversion is averaging 4.0, well mature. Fruit firmness dropped to an average of 17.3 lbs. Brix has been relatively stable the last two weeks at close to 13 brix. Fuji is highly susceptible to watercore, which becomes more of a problem on fruit harvested past optimum maturity. The predicted harvest date for central Berrien County is Sept. 24. 

Golden Delicious

This is the fourth week of sampling. Fruit background color is losing the green hue. Starch conversion has moved from an average of 3.9 for last week to 4.8 for this week, with 3.0 considered mature. Firmness is 16, below the threshold of 17 for long-term controlled atmosphere storage. The predicted harvest date for central Berrien County is Sept. 24. Storage of this variety is best at 32 - 33 F in air or CA storage. Golden Delicious can lose water relatively rapidly in storage if humidity is low.

Red Delicious

This is the fourth week of sampling. Starch conversion is averaging 3.9, up from 2.9, with 2.5 as the threshold for mature. Current fruit firmness is at 15.9, with the threshold of 18 for best longterm controlled atmosphere storage. Fruit maturity is somewhat ahead of the predicted harvest date for Red Delicious for central Berrien County of Sept. 29.

IdaRed

This is the third week of sampling. Fruit background color is still relatively green. Starch conversion is averaging 2.3, with 3.5 considered mature. Firmness is about the same as last week, now averaging 16.4 lbs. The predicted harvest date for IdaRed for central Berrien County is Oct. 6.

Rome

First samples were taken this week. Internal starch is averaging 3.5, with 3 considered mature. Firmness is still excellent at 20.4 lbs. Predicted harvest date for central Berrien County is Oct. 6.

Braeburn 

First samples were taken this week. Internal starch is averaging 2.9, immature. Firmness is still excellent at 21.7 lbs. Harvest can be delayed waiting for more sugar development. Predicted harvest date for central Berrien County is Oct. 21.  

Apple maturity sampling parameters

• Color % = the visual percentage of red color (blush) from 0 to 100; range is of all fruits tested.
• Firmness in pounds pressure = measured with a FT Penetrometer; range is based on averages for orchards tested.
• Starch: 1 = all starch, 8 = all starch converted; range is based on averages for orchards 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.

Predictions are for the first significant harvest date rather than peak harvest. Also note that the normal harvest date for Fuji is approximately three weeks ahead of the normal date given in previous years reports. Newer strains of Fuji have much earlier and more extensive red blush development than older strains. In the past harvest of Fuji was delayed past optimum internal maturity to wait for better blush development. This delay has resulted in increased storage problems, including watercore and internal browning.