MSU Extension Apples

Apple maturity testing will occur weekly for the Grand Rapids, 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 Grand Rapids region, Jonagold and Empire are being harvested. Golden Delicious and Ambrosia are mature according to the starch rating and are still very firm. Red Delicious, Fuji and Idared are still immature.

Maturity dates are tracking more closely to last year with varieties being harvested about two weeks ahead of normal. High heat in August and September seems to have significantly advanced growing degree days and maturity later in the season. Be sure to monitor your blocks to harvest at the optimal maturity stage for each variety and target storage conditions. Communicate this information to packers and processors to facilitate proper storage and optimize fruit quality.

With advancing maturity, applications of pre-harvest management tools may be needed to help maintain fruit quality and manage labor. For later maturing varieties, a product like aminoethoxyvinylglycine (AVG; ReTain) can be used, and applications at 28, 14 or seven days before harvest are recommended. For a 1-MCP product (Harvista), applications are recommended closer to harvest at seven or three days.

Weather over the past week was hot with low temperatures in the 50s and highs in the 70s and low 80s across the region, according to the Sparta Enviroweather station. Average temperatures are above normal for this time of year. Day and nighttime temperatures will be similar over the next few days with highs in the 80s and lows in the 40s and 50s. Conditions are forecasted to be dry for the rest of the week. 

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 locations in Kent County.

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

• Predicted apple harvest dates for 2024 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.
• New starch charts for evaluating apple maturity in Michigan from Michigan State University
• Predicting apple maturity and starch chart from Cornell University.
• Starch chart for Honeycrisp Apples developed by Washington State University.

Maturity information for the Grand Rapids region

Empire

Empire fruit were sampled from one location in Sparta. Fruit were treated with ReTain. Red color is very good and averaged at 91% red color. Background color is yellow green. Fruit firmness has decreased slightly from last week and is at 17.7 pounds of pressure. Starch rating is at an average of 3.9 which is similar to last week, and sugars are at 12.5 Brix. Average fruit diameter is 2.8 inches.

*Average values from all dates are reported from one sampling location.

Golden Delicious

Golden Delicious were sampled from two locations in Sparta. There is a slight blush on some fruit covering an average of 25% of the fruit surface, and background color is green. Fruit firmness is at 17.4 pounds of pressure. Starch is at 7 on average, and sugars are excellent at 14.8 Brix. Average fruit diameter is 2.6 inches. According to the following table, Golden Delicious are mature and are ready for harvest. Some locations have harvested Golden Delicious already.

Ambrosia

Ambrosia were sampled from four locations in Sparta. Fruit have excellent red cover for Ambrosia with 61% red color over the fruit surface, and the background color is yellow green. Fruit firmness is at 17.7 pounds of pressure. Starch is at 6.4 on average, and sugars are excellent at 14.9 Brix. Average fruit diameter is 2.8 inches. Be sure to check Ambrosia fruit every few days to test for maturity at individual orchard locations. This variety can quickly change from immature to mature.

Fuji

Fuji fruit, which includes Aztec Fuji, were sampled from four locations in Sparta. Fruit were treated with ReTain. Red color is an average of 73%, and background color is green. Fruit firmness is at 19.3 pounds of pressure. Starch is at 2.8, and sugars are good at 12.7 Brix. Average fruit diameter is 2.7 inches. Fruit are almost mature. For long-term storage, recommended pressure is 18 pounds, and the recommended starch rating is 3.

Red Delicious

Red Delicious fruit were sampled from three locations in Sparta. Red color is 92%, and background color is yellow-green. Fruit firmness is at 17.8 pounds of pressure. Starch is at 2.6, and sugars are good at 12.6 Brix. Fruit are still immature. Average fruit diameter is 2.7 inches.

Idared

Idared were sampled from four locations in Sparta. Red color is an average of 75%, and background color is green. Fruit firmness is at 15.9 pounds of pressure. Starch is at 2.2, and sugars are good at 12.3 Brix. Average fruit diameter is 3 inches. Fruit are almost mature. For long-term storage, recommended pressure is 16 pounds, and the recommended starch rating is 3.5.

Apple maturity sampling parameters

• 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 For Honeycrisp: will typically be rated using the standard Michigan State University starch 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.