MSU Extension

General comments

Welcome to the first of many Michigan State University Extension apple maturity reports from the Grand Rapids, Michigan, area fruit team. As you know, many changes in apple physiology occur over time as fruit become more mature—starch is converted to sugar; seeds turn a darker color; acidity decreases; chlorophyll levels decrease; respiration increases; cell walls weaken; fruit begins to soften; and ethylene production increases. Our MSU Ridge Apple Quality lab measures many factors to help you make harvest management decisions. We are graciously funded by the Michigan Tree Fruit Commission, Michigan Apple Committee, Michigan State Horticulture Society and MSU Extension. Many thanks go out to all the growers and industry representatives that donate to our program as well.

In the Grand Rapids area, apple maturity seems to be running just about right in line with our predicted harvest dates or about five days ahead of normal average dates for early varieties (see the table below for predicted harvest dates). Paula Red and Gingergold harvest is completed on the Ridge with good color and overall quality being reported.

Fruit color has been lacking a bit all summer, but has greatly improved with the cooler temperatures over the past two weeks. Size has been average or a bit on the small size where irrigation is not present, but size, too, is improving greatly in the last two weeks. Gala will be the next major variety for harvest for long-term controlled atmosphere (CA) storage in the Grand Rapids area. Blocks with Fulford Gala and known early sites will get started first.

McIntosh are getting close for long-term CA. Honeycrisp are a week or so away from any first picking of those first to ripen fruits. In our sampling, we are noticing a bit of variability in the maturity of all varieties tested so far. This is expected due to the long and drawn out bloom period this spring.

We are seeing some water core in early harvested susceptible apple varieties so far this season. The presence of water core at this time seems to be similar to 2016 so far. The lack of rainfall recently will likely lessen water core for early varieties.

Some sunburn can be found, but not as prevalent as in 2016 so far.

Variety sampling results

Strains are noted where applicable. We try our best to collect samples from blocks untreated with harvest management products.

Gala color is good to very good on most strains this year and continues to improve. The warmer weather predicted for this week might slow color development a bit if the nights stay warm. Size is OK to good, depending on fruit set. Gala have moved towards maturity from early sampling over three weeks—watch individual blocks very carefully.

Our predicted harvest date for Gala for long-term CA storage is Sept. 5 and it’s looking like this date is accurate for early harvest. We normally like to recommend a starch index of 3 for long-term storage of Gala, but if color and size are where you need them, you could pick for long-term CA storage at a starch index of 2.

McIntosh are not quite there yet in the general Grand Rapids area, but getting close. Internal ethylene is nearly non-existent with these early samples with no fruits over the 0.2 ppm climacteric. This is good given the warmer weather predicted and should help keep drop at a minimum for the next week or so. Pressure readings are indicating very good firmness at an average of 16.5 pounds in this week’s samples. Color is excellent, of course, on Ruby Mac and good to very good in other Mac strains and improving every day. Brix reading is good at 12.4 and improving each week.

Harvest for long-term storage of Macs can begin at any time color is right, with the majority of harvest coming in seven to 10 days. Our predicted harvest date for peak Mac harvest is Sept. 5. Be watchful in blocks with heavy fruit set as drop could occur from fruits pushing themselves off.

Honeycrisp are moving rather quickly toward maturity, with some fruits already in the category for early harvest for fresh (we call them shiners). Watch your sites carefully. Firmness readings are very good to excellent at an average of 17.5 pounds for this week’s samples. Starch readings are quite variable for Honeycrisp, which isn’t all that unusual. Starch clearing is much lower than this time last year, most likely due to recent cooler temperatures. Brix level is good, but not yet excellent at 12.6.

Our predicted harvest date of Sept. 15 seems accurate for a peak harvest of Honeycrisp around the Ridge. Watch your Honeycrisp blocks closely—multiple picks are going to be necessary to deal with the maturity variability on trees due to the long pollination period.

Apple maturity sampling parameters

• Percent 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 percent = 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 the Cornell Starch Iodine Index Chart.
• Brix = percent 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, including:

• Tools to help manage apple harvest
• Why does apple fruit drop prematurely?
• Starch chart for Honeycrisp apple fruit
• Lenticel infections and bitter rot of apples
• Checking apple maturity: What to look for