MSU Extension Apples

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

In the west central region, growers are harvesting some early strains of Gala, such as Pacific and Brookfield. McIntosh and Honeycrisp are maturing, and some growers have picked McIntosh. September Wonder Fuji are also maturating but this varied by location. Jonagold and Empire are still immature.

Weather over the past week has generally been warm with rain showers. Daytime temperatures have ranged from the low 70s to low 80s, and nighttime temperatures have been in the 50s and 60s. Ideal temperatures for red color development are highs in the upper 70s and lows in the upper 50s. 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. 14, the MSU Enviroweather station for Hart has reported an accumulation of 3399 DD₄₂ and 2422 DD₅₀. Scattered rainfall occurred on Sunday and Tuesday this week, Sept. 11 and 13, across the region.

With regular rain events, growers should maintain fungicide coverage to minimize late season rots, particularly for fruit that will be in long-term storage. Rainfall over 2 inches can wash off fungicide residues on fruit. 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 will 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 three to five locations across Oceana County.

For more information about apple maturity testing, review these resources compiled by Anna Wallis and Amy Irish Brown, MSU Extension.

• 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.

Maturity information for the west central region

Gala

Early samples of Brookfield Gala and Pacific Gala were collected at 3 locations on Sept. 12 in Oceana County. Generally, fruit is at a stage where it could be picked for short-term CA storage according to Gala recommendations in the table below. Fruit size has improved with recent rainfall, especially in blocks with a moderate crop load. Red color is also improving, and some blocks are highly colored depending on the Gala strain. Background color is improving and becoming more yellow with a creamy color. Firmness is decreasing with an average of 16.3 lbs. Sugars are increasing, and fruit starch was variable from site to site with some fruit staining at 2 (little starch conversion detected) and other fruit staining at 8 (majority of starch converted). Some shoulder cracking has been observed in other regions of the state due to recent rains.

September Wonder Fuji

Fruit were sampled at three locations on Sept. 12 in Oceana County this week. Fruit have advanced over the past week with increases in size and color development. Average red color development is about 60%, and background color is turning to pale green. Starch is clearing, and sugars levels are increasing slightly.

Honeycrisp

Fruit were sampled from three locations on Sept. 12 in Oceana County. Fruit continue to size with some fruit being quite large. Red color development is also increasing to an average of 72% red color. Background color is changing slightly to yellow. Fruit firmness is also decreasing, and starch is clearing to an average of 5.9 Starch clearing varied with some fruit staining at 1 (little starch conversion detected) and other fruit staining at 8 (majority of starch converted). Average sugar levels are increasing and are considered excellent 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. High bitter pit-risk fruit should be cooled quickly to the recommended 38 F 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 68°F (room temperature) for five to seven days.

Empire

Fruit were sampled from three locations on Sept. 12 and 13 in Oceana County. Red color development is good with an average of 68.7%. Background color is still quite green. Average fruit firmness is at 16.2. On average, starch clearing is light, and sugars levels are still considered low according to the Brix table below.

Jonagold

Fruit were sampled from three locations on Sept. 12 in Oceana County. Red color development is good, and background color is light green. Fruit firmness varied from site to site with an average of 16.0. On average, starch clearing is low at 2.2, and sugars levels are good 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 Maturity page for regional reports throughout the state and additional resources.