MSU Extension Apples

This is the fifth 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 – Over the past week, weather in the Grand Rapids, Michigan, area was much cooler than previous weeks. Highs were in the 70s degrees Fahrenheit most days and lows were in the 50s most nights. Scattered storms on Sept. 7 occurred across the region, including high winds and some rainfall. Farther north, there were reports of large (golf ball sized) hail, but it appears to have lasted only a few seconds and missed most production areas. More information about storm reports (past and present) can be found on the NOAA Storm Prediction Weather Website. Scattered precipitation is expected this Saturday and again early next week. Hotter and drier than normal is expected for the remainder of fall.

Overall, the summer has been warmer and wetter than normal. The Detroit, Michigan, area saw the most precipitation across the state, while the Grand Rapids areas experience approximately 125% of the normal accumulated precipitation from June 1 – Aug. 1. Temperature departures for the Grand Rapids area were about 3-4 F warmer than normal for this period.

Gala – Untreated fruit began harvest at the end of last week and through the holiday weekend. Fruit treated with PGRs began picking this week in many locations.

Honeycrisp – Spot picking may begin by the end of this week or early next week. Color is poor, but internal qualities indicate fruit is approaching maturity.

McIntosh (Ruby Mac) – Approaching maturity, picking may begin next week.

Jonagold, Jonathan, Golden Delicious, Ambrosia, Empire – These varieties are beginning to show signs of ripening. Starch clearing is just beginning 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 5-7 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

Standard Honeycrisp still has poor color in most places; background color is just beginning to change from green to yellow, and red color is still minimal. However, other parameters indicate first pick fruit is fairly mature. As is typical for this variety, there is a wide range of maturity. In fruit sampled this week, sugars, starch and firmness indicated first pick fruit should be harvested in the next week. This variety matures similarly to other fruit, except for pressure (which can be much lower at maturity than many other varieties).

Starch ranged the entire spectrum of scale in fruit sampled this week. Fruit were more advanced in locations farther south (Fennville, Michigan) and starch clearing in this variety shows a considerably different pattern than other varieties. Fruit evaluated showed a wide range in starch pattern. This week and previous weeks, we have used the new starch chart developed by WSU to evaluate fruit. Refer to this starch chart (which uses a 1-6 scale and unique staining pattern) for maturity evaluation.

Bitter pit was detected in a couple of fruits in one location; in this location fruit was considerably larger and crop lighter than other locations. We are doing research to evaluated prediction methods for Michigan Honeycrisp production. One method (the passive prediction method) includes harvesting fruit approximately three weeks before harvest and observing bitter pit development in these samples at harvest. In fruit harvested three weeks ago from over 30 blocks as part of a research trial, we have only observed very minimal bitter pit development, indicating lower risk of bitter pit in these blocks this year.

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

Honeycrisp sampled Sept. 6

*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 is harvesting now or very close to harvest in most places. Untreated fruit were picked mostly last week or the beginning of this week. Fruit treated with PGRs are nearing maturity in many locations, dependent on treatment. While PGRs are providing some delay of harvest, the effect is slightly diminished due to the hot weather two and three weeks ago.

Color spanned a wide range in samples collected this week, depending on strain and location. High coloring strains (Buckeye, Gale) have excellent color, while other strains have somewhat poor color. A high coloring strain does not necessarily indicate earlier maturity, so it is important to pay attention to other maturity indicators. There is a very good crop in most locations, size is still small but will improve quickly over the coming weeks. Some frost damage is apparent in blocks in the form of russeting, lopsided fruit, and ridging.

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 applied twice, either 28 plus seven 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.

Gala – ReTain applied Sept. 6

Gala – Weekly averages

*Starch values according to the 1-6 scale developed by WSU

Gala – ReTain Treatment Comparisons

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

Ruby Mac

This variety is beginning to show signs of maturity. Color is excellent in most locations. Starch, pressure and sugars indicate the fruit is just beginning to enter the harvest window. This season is generally about five to seven days ahead of normal, with respect to heat accumulation. Harvest is also, slightly ahead of normal. With cooler weather this week, we can expect this and other later varieties to slow down in their development.

Ruby Mac sampled Sept. 6

Ruby Mac Weekly Averages

Golden Delicious

This variety is just beginning to show signs of maturity. Color is still very green, pressure is high and sugars still low. Starch clearing is just beginning and should be watched closely.

Jonathan

This variety is also beginning to show early signs of maturity. Color is excellent. Starch clearing is beginning, firmness is still a little high and sugars a little low. Typical harvest date is approximately Sept. 20. This season, which is approximately five to seven days early, we expect fruit to be entering harvest window for long term storage approximately Sept. 15—which is next week. Maturity indicators should be watched closely.

Jonagold

Similar to other varieties, Jonagold is also showing early signs of maturity, with regard to starch clearing, sugars and firmness. Color is still very green and red color development minimal.

Ambrosia

Ambrosia is a newer variety for our region, and we are taking samples in order to improve our understanding of the fruit for our region. Trees where samples were collected are still young, in the first few years of establishment. Fruit is still very immature, although it is already producing ethylene. Color and starch clearing is minimal. More to come next week.

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.