MSU Extension Apples

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

Harvesting of late season apple varieties is proceeding quickly aside from some recent delays due to rain. Scattered sleet was seen Monday and Tuesday this week, but temperatures were generally above 35 Fahrenheit and not a danger to fruit quality. Some watercore is appearing on some late varieties including Braeburn and Evercrisp. Overmature varieties, such as Red Delicious and Fuji, are showing quite a bit. Cloudy days are less conducive to watercore development by apples because photosynthesis, a cause of sorbitol-rich liquid buildup in the flesh, is inhibited. 

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, Red Delicious, Yellow Delicious and IdaRed 

No more testing. Fruit of these varieties are generally well mature.

Rome

For this variety, the internal starch index is averaging 5.2, compared to 4.0 last week--3 is considered mature. Firmness dropped approximately 2 lb since last week and is currently averaging 17.8 lbs. Predicted harvest date for central Berrien County is Oct. 6.

Braeburn 

This was the third week of sampling. Internal search is averaging 5.0, a jump from last week’s 3.6.  Firmness dropped 2 lbs since last week and is now averaging 19.2. Some watercore was detected in samples from one of 5 sites sampled. Harvesting is recommended for sites testing similar to these samples. This is in line with the predicted harvest date for central Berrien County of Oct. 21.

Evercrisp

This is the second week of sampling for this variety. The current average starch reading is 3.6 and firmness is still excellent at 20.8 lb. Penn State University has recommended using starch index of 4-6 for long term storage and 6-7 for direct sales markets. Red blush development is decent for fruit that are well exposed to sunlight. Evercrisp is a tip-bearing variety and may need special attention to pruning to avoid excessive shading in the lower canopy. Evercrisp, like one of its parents Fuji, is prone to watercore and internal browning in storage if picked too late. Watercore started showing up in one of three sites tested this week.

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.