MSU Extension Apples

This is the sixth apple maturity report for the 2021 harvest season. Reports are sent out every week (usually on Wednesdays), following the Michigan State University Extension fruit team apple maturity calls on Wednesday morning.

For general information about how samples are collected and processed, please refer to Apple Maturity Report #1.

• Considerations for the 2021 harvest season can be found in this article.
• 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.

How to read the maturity tables

For each variety evaluated, we provide data from our evaluations in a table. In each, a row is provided for each sample tested. This allows you to see how the varieties may be progressing in different regions or specific locations. An average is included 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. Recommended values are included for each variety at the bottom of the table. These suggested values for firmness and starch index were also published in a standalone table format. Firmness ranges encompass long and short-term storage recommendations.

Updates for this week

Weather – In the Grand Rapids, Michigan, area over the past week, we have had considerably better weather for maturity and harvest. Temperatures have been cooler, with highs in the 70s degrees Fahrenheit and lows in the 50s lending to better color and quality development. There have been a number of storms over the past week, including prolonged thunder with variable rain on Sunday evening, followed by widespread heavy rain on Monday, contributing over 1 inch of accumulation in most areas. In addition, there have been isolated storm events in many places over the past days, with heavy rains and strong winds, which have contributed to some early fruit drop.

Gala – Harvest is in full swing. Untreated fruit has been harvested. Fruit treated with PGRs harvesting now, but wide range of maturity.

Honeycrisp – First pick is happening now.

McIntosh (Ruby Mac) – Untreated fruit past mature. Fruit treated with plant growth regulators (PGRs) harvesting now, but wide range of maturity.

Jonagold, Jonathan, Golden Delicious, Ambrosia, Empire, Red Delicious, Ida Red – These varieties approaching harvest windows and should be watched closely.

Predicted harvest dates according to the Maturity Model in Enviroweather are about 10 days earlier than normal for early varieties (Gala, Honeycrisp, McIntosh). At this time, the season appears to be between five to seven days ahead of normal.

Mixed maturity is evident in most varieties and locations. Multiple picks may be needed to harvest fruit at the appropriate maturity for successful storage conditions.

Honeycrisp

First pick fruit is mature now and harvest has begun. Red color has improved greatly over the past week, although it is still less than excellent in most locations. However, maturity parameters indicate fruit is ready to pick. Ethylene levels were very high in fruit sampled this week; starch clearing is considerable in most fruit.

There are two starch charts frequently used to evaluate this variety. The Cornell starch chart has been used historically to evaluate most varieties and ranges 1-8. However, the starch clearing pattern is very unique in Honeycrisp and a Honeycrisp-specific starch chart was also developed by WSU, which ranges 1-6. We have used both charts in our evaluations, depending on the location and lab in which they were tested. We apologize for any confusion this has caused. We are in the process of developing additional starch charts for this and other varieties to resolve some of the difficulty of interpretation.

This variety is susceptible to several fruit spots. Lenticel damage has been observed in many locations across the region. Bitter pit has only been observed in very few locations. These two kinds of spots can be difficult to distinguish. Lenticel damage typically has defined edges and is associated with a lenticel, while bitter pit has sunken, irregular, mostly diffuse edges (photos below).

Lenticel disorders are most likely related to physiological stress from earlier in the season, frequently associated with moisture (too much or lack thereof), as well as sunburn, and chemical injury. This chart of lenticel related disorders developed by Washington State University and USDA scientists is useful for describing various symptoms. In addition, this presentation describing fruit rots and lenticel injury from Cornell University given by David Rosenberger and Srdjan Acimovic helps tease apart the various types of injury on Honeycrisp and other varieties.

Lenticel damage can also lead to lenticel infections, as summarized in this article on lenticel infections and bitter rot by Bill Shane, MSU Extension. But there are many contributing factors and unknown causes of lenticel injury.

The most recent Honeycrisp Virtual Meetup was on the topic of Harvest and Postharvest management of Honeycrisp with Dr. Randy Beaudry, Chris Watkins, and others. You can find the recording on the MSU Kaltura Mediaspace Website.

Honeycrisp sampled Sept. 13

*Starch was rated on the 1-6 scale developed by WSU, except for the samples indicated (*) which were rated on a 1-8 scale developed by Cornell.

Honeycrisp Weekly Averages

Gala

Gala harvest is in full swing now. Fruit that was untreated is beyond optimal maturity for controlled atmosphere (CA) storage and should be marketed for fresh sales if possible. For fruit that has been treated with PGRs, maturity spans a wide range. This is the case across the region as well as within individual blocks. The photo below shows starch staining of fruit from a block treated with ReTain, in which fruit show both very little and nearly complete starch clearing. Overall, across the region Gala is being harvested or very close to harvest now. In some locations fruit cracking has been observed, particularly in over-ripe fruit.

In a side-by-side ReTain treatment trial, summarized below, we can see the effects of different ReTain programs. ReTain was applied at a full rate one, three or seven days before harvest (DBH), or a half rate was a applied twice, either 28 plus 7 or 28 plus three days before harvest. The results illustrate that the earlier applications of ReTain delay harvest (all maturity parameters) the most. Although treatments have been slightly less effective than we would expect in a cooler year. As we continue to take data on this trial, we expect to see more effect of later ReTain applications as harvest goes on.

Gala (ReTain treated) Sampled Sept. 13

Gala – Weekly averages

Gala – ReTain Treatment Comparisons Sept. 13

*Application rate was 1 pouch per acre. This was applied all at once in treatments with one application or split into ½ pouch per acre in treatments with two applications.

Ruby Mac

Most fruit have been picked or will be in the next week, depending on PGR treatments. Maturity parameters indicate fruit is well within the harvest window, and some fruit is overripe. Some bleeding was observed in untreated fruit this week, which is not unusual, given the high anthocyanin content and pigmentation of this cultivar (photo below).

Ruby Mac sampled Sept. 13

Red Delicious

This variety is already showing signs of maturity. Red color is very good in most locations, depending on strain. Background color is still fairly green. Firmness and starch are just entering the recommended ranges for harvest for long term storage. Sugars are just a bit low, which is typically more acceptable for this variety. Keep in mind this variety has a thick skin, which may mask the overall internal maturity of the fruit.

Red Delicious sampled Sept. 13

Golden Delicious

This is the second week we tested this variety. Background color is still fairly green but improved from last week’s testing. Minimal red color was observed, with only a touch of blush on a few fruits. Evaluation of starch clearing, firmness, and sugars all indicate fruit is very close to harvest and should likely begin picking within the next week. Flavor of fruit is also showing noticeable development.

Golden Delicious sampled Sept. 13

Jonathan

This variety is showing a wide range of maturity. Projected harvest dates, as predicted by the Enviroweather models, indicated the last week of September (approximately Sept. 30) as the anticipated harvest date. We appear to be very close to this prediction. Red color is excellent in most locations. There is considerable starch clearing in some fruit while other fruit still is very starchy. Firmness also shows a wide range within individual blocks.

Jonathan sampled Sept. 13

Jonagold

This variety was also sampled for a second time. Red color development is still less than excellent and background color somewhat green but improving. Fruit size is excellent, as large fruit size is typical for this variety, especially in places where there is a light crop this year. Typical harvest is approximately the same timeframe as Jonathan, and maturity parameters indicate this is expected for the current season. Harvest will likely begin as early as next week.

Jonagold sampled Sept. 13

Ida Red

This variety was tested for the first time this week. Fruit is showing movement towards in some locations, while other locations fruit is still very green. Red color is very good and size adequate. Starch clearing, firmness and sugars all indicate the fruit Starting to move in the right direction towards maturity. Our predicted harvest date for Ida Red is Oct. 7. Watch this variety closely and harvest for your market.

Ida Red sampled Sept. 13

Empire

This variety was sampled for the first time this week from one location. Fruit is still fairly green, although it is beginning to show signs of maturity. Typical harvest is usually just after Jonagold and Jonathan and will likely begin in a couple of weeks.

Empire sampled Sept. 13

Ambrosia

This is the second week this variety was tested. Ambrosia is still a new variety for the area and we are learning about maturity for our region. The fruit is still immature, with less than excellent red color development, and green background color. It appears to be a heavy ethylene producing apple, with many fruit producing significant amounts in our sample last week and again this week. Starch clearing is difficult to interpret, with an interesting mosaic pattern. Clearing appears to begin throughout the flesh even while some of the cortex is still not clear (photo below). Overall, this variety needs a little more time and may begin harvest as early as next week on young trees and early sites.

Ambrosia sampled Sept. 13

Apple maturity sampling parameters

• % 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
• 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.
• 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.