MSU Extension Apples

Apple maturity testing will occur weekly for the west central Michigan region beginning now through the end of harvest. Reports will be sent out every week following the Michigan State University Extension fruit team apple maturity calls on Wednesday mornings.

In the west central region, growers are finishing harvest of early varieties such as Minneiska and Premier Honeycrisp. For Gala, some early strains, such as Pacific and Brookfield, may be ready to pick for long-term storage. McIntosh and September Wonder Fuji are showing signs of maturity development but are still immature. Honeycrisp are maturing faster than expected, and some growers should consider harvesting according to long- or short-term storage requirements.

Weather update

The weather over the past week has generally been hot. Daytime temperatures have ranged from the upper 70s to high 80s degrees Fahrenheit, and nighttime temperatures have been in the mid to upper 60s. Ideal temperatures for red color development are highs in the upper 70s F and lows in the upper 50s F. Red color development has been limited over the past week, but as temperatures cool down the rest of the week, color will improve. Bright and sunny conditions enhance photosynthesis and sugar accumulation. Cool night temperatures decrease respiration and the breakdown of sugars. Therefore, more sugars can remain in fruit and can be used to produce anthocyanins which are responsible for red color development.

As of Sept. 6, the Michigan State University Enviroweather station for Hart has reported an accumulation of 3,207 growing degree days (GDD) base 42 and 2,115 GDD base 50. Scattered rainfall occurred on Wednesday, Sept. 6, and in the early morning hours of Sept. 7 across the region.

The Hart Enviroweather station reported a total of 0.32 inches of rainfall on Sept. 6. This is much needed rain as soil moisture levels continue to be dry this season in the west central region. Soil moisture content is reported to be 1.3% and 1.4% at 4 and 20 inches soil depth, respectively, for the Hart Enviroweather station.

As a reminder, rainfall over 2 inches can wash off fungicide residues on fruit. Growers should maintain fungicide coverage to minimize late season rots, particularly for fruit that will be in long-term storage. Excessive rain may also have an impact on fruit by temporarily diluting flavor and brix (sugars).

How to read maturity tables

Each week, an apple maturity report will be provided and include average values for several apple samples for varieties nearing maturity. Maximum and minimum values are included in tables below for the highest and lowest individual fruits evaluated for each to give a full spectrum of maturity. All samples included in the reports have been untreated with ReTain or Harvista, unless otherwise noted. Samples were collected from two to four locations across Oceana County.

For more information about apple maturity testing, review these resources compiled by the MSU Extension tree fruit team:

• Predicted apple harvest dates for 2023 from MSU Extension.
• More information on harvest management tools and timings can be found in this article.
• Guidelines from MSU Extension 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.

Maturity information for the west central region

Minneiska

Fruit were sampled at three locations on Sept. 5 in Oceana County. Minneiska (SweeTango) is an early apple with bright color. Some growers have finished first pick for this variety. Fruit sampled for maturity testing was remaining on the trees after first pick. Fruit are close to maturity and sugars are excellent. Red color development is increasing; however, some fruit have russet this season. Background color is also changing to yellow. Starch is clearing in the cortex, and sugar levels are at 13.7 Brix.

Gala

Early samples of Brookfield Gala and Pacific Gala were collected at three locations on Sept. 5 in Oceana County. Generally, fruit is still immature. Fruit size is improving and will increase with recent rain events. Red color is also improving, and some blocks are highly colored depending on the Gala strain. Background color is changing from light green with some yellow. Fruit are still firm with an average of 19.5 pounds. Sugars are increasing, and fruit starch is still low at 1.9. Starch is being converted to sugar at the core.

September Wonder Fuji

Fruit were sampled at two locations on Sept. 5 in Oceana County this week. Fruit are generally immature. Red color development is moderate and background color is turning to light green and yellow. Starch is beginning to clear at some locations and sugars levels increased slightly from last week.

Honeycrisp

Fruit were sampled from three locations on Sept. 5 in Oceana County. Fruit are sizing well. Red color development is at 64.8% red color which should improve with the cool weather later this week. Background color is green and fruit firmness is 15.6 pounds. Starch clearing is at an average of 5. Sugar levels are increasing and are considered good according to the Brix table below.

Bitter pit has been observed in some locations. Fruit that are high risk or are more susceptible to bitter pit development may be in blocks with younger trees, high-risk rootstocks or high-vigor trees. Large fruit are also more susceptible to bitter pit development than small fruit. Fruit with high risk of bitter pit should be cooled quickly to the recommended 38 degrees Fahrenheit storage temperature, as conditioning will exacerbate bitter pit. High risk fruit should be marketed as soon as possible. Fruit intended for longer-term storage should be pre-conditioned, with recommended conditions of 50-60 F for five to seven days. MSU Extension has more recommendations for Honeycrisp conditioning and storage.

RubyMac

Fruit were sampled from three locations on Sept. 5 in Oceana County. Red color development is increasing and background color has changed slightly but is still green. Fruit firmness was similar over the past two weeks. On average, starch clearing is moderate, and sugars levels are excellent according to the Brix table below.

Apple maturity sampling parameters

• Ethylene (% 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. Indicates surface area covered in red and intensity of red color.
• 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.
• Starch for Honeycrisp: will typically be rated using the standard Cornell SPI scale (1-8). However, a separate starch chart for Honeycrisp apples developed by Washington State University (scale 1-6) also exists.
• Brix = % sugar measured with Atago PAL-1 Pocket Refractometer.

Looking for more? View Michigan State University Extension’s Apple page for regional reports throughout the state and additional resources.