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. 

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.

Fuji (Main season)

Starch conversion is averaging 4.9, well mature. Fruit firmness dropped almost a pound over the past week to an average of 16.7 lbs. Brix made a jump to 14.1, up from 12.8 last week. Red blush has improved, now averaging 81% red. Fuji is highly susceptible to watercore, which becomes more of a problem on fruit harvested past optimum maturity. Two of six sites sampled had significant watercore. The predicted harvest date for central Berrien County is Sept. 24.

Golden Delicious

This is the fifth week of sampling. Fruit background color is losing the green hue. Starch conversion has moved from an average of 4.8 last week to 6.8 for this week, with 3.0 considered mature. Firmness is 16 lbs, below the threshold of 17 for longterm controlled atmosphere storage. The predicted harvest date for central Berrien County is Sept. 24. Storage of this variety is best at 32 – 33 Fahrenheit in air or CA storage. Golden Delicious can lose water relatively rapidly in storage if humidity is low.

Red Delicious

This is the fifth week of sampling. Starch conversion jumped again, now at 5.2 compared to 3.9 for last week, with 2.5 as the threshold for mature. Current fruit firmness average now is down to 15.0 lbs, with the threshold of 18 for best longterm controlled atmosphere storage. One of four sites sampled had significant watercore symptoms. The predicted harvest date for Red Delicious for central Berrien County of Sept. 29.

IdaRed

This is the fourth week of sampling. Starch conversion is averaging 4.0, a jump from last week’s 2.3, with 3.5 considered mature. Firmness dropped about 1 pound since last week, now averaging 15.3 lbs. Some sites are showing slight watercore in fruit. This variety is on target with the predicted harvest date for IdaRed for central Berrien County of Oct. 6.

Rome

For this variety, the internal starch index is averaging 4.0, with 3 considered mature. Firmness is still excellent at 19.7 lbs. Predicted harvest date for central Berrien County is Oct. 6.

Braeburn 

This was the second week of sampling. Internal starch is averaging 3.6, up from 2.9 for last week. Firmness is still excellent at 21.3 lbs. Harvest can be delayed waiting for more sugar development. Predicted harvest date for central Berrien County is Oct. 21.

Evercrisp

First samples were taken this week. The current average starch reading is 2.7. Penn State University has recommended using starch index of 4-6 for long term storage and 6-7 for direct sales markets. Evercrisp, like one of its parents Fuji, is prone to watercore and internal browning in storage if picked too late. No watercore was detected in the samples from the Berrien County region.

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.

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.

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 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 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.