MSU Extension

General comments

In the Grand Rapids, Michigan, area, apple maturity continues to follow our predicted harvest dates pretty closely. There are some sites and cultivars ahead of the dates and with the mixed maturity on many trees, some fruits are behind these dates. Continue watching your blocks closely as maturity continues to change quickly in many varieties so far in the harvest season. Perhaps the cooler weather settling in will slow maturity – it certainly will help with color development. See the table at the end of this article for details on apple storage parameters for different varieties.

Many Gala blocks have been stripped in the general Grand Rapids area. Honeycrisp will be the next major variety for harvest as color and flavor develops. For the Hart/Shelby area, growers can expect harvest dates to be behind the Grand Rapids area using this guide: along the lakeshore approximately six days behind Grand Rapids; areas inland about four days behind.

Water core

Given the high amounts of rain that some areas have received in the last six weeks, you should be paying close attention to water core in varieties that are highly susceptible to it this season and harvest accordingly. High water core presence reduces storage-ability.

Fruit rot potential

Fruit rot potential is higher than usual for the 2016 season due to high amount of rainfall in the recent several weeks. The best place to manage fruit rots is with fungicides applied while fruit are on the tree. We don’t dip any longer and fungicides were added to the DPA. We fog with DPA, but the post-harvest fungicides are no longer routinely used. With a big crop potential, it is likely that fruit will be stored a long time with more potential for rot to develop.

Superficial (storage) scald

Very warm temperatures in August and September and possible poor red color could lead to higher incidence of scald in susceptible varieties. Treat fruit rapidly after harvest with DPA or 1-MCP to minimize risk.

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.
• Brix = % sugar measured with Atago PAL-1 Pocket Refractometer

Variety sampling results

Many Gala blocks on the Ridge have been stripped. For Gala not treated with harvest management materials, they are now in the short-term storage window.

McIntosh harvest for long-term storage can begin at any time color is right. With the exception of firmness and starch conversion, all maturity indices for McIntosh have remained unchanged. This in not atypical of McIntosh. If untreated with 1-MCP or AVG, McIntosh in general are ready for long-term controlled atmosphere (CA) storage at this time. Once internal ethylene begins to increase, they will quickly move out of best condition for long-term storage.

Honeycrisp seemed to just start the fall season with high maturity levels, but keep in mind we are testing fruits that are most likely to be harvested next – we don’t test the greenest fruits, nor do we take a random sample of all fruits. We feel this tells you what to expect next. Watch your sites carefully. This will be a good year to not skip harvest management tools (AVG or Harvista). When Honeycrisp are in the very mature range, they are more subject to chilling injury in storage.

Firmness readings are still very good to excellent, but have dropped from an average of 17.1 pounds last week to 15.6 pounds this week. The range across all fruits tested is extremely variable, and not unusual for Honeycrisp. Starch readings continue to be higher than expected. Brix level has made a definite positive movement from 11.8 last week to 13.6 this week. Honeycrisp eat OK, but they need a little time to develop their depth of flavor for fresh sales. Our predicted harvest date of Sept. 10 now seems a little early for peak harvest of Honeycrisp around the Ridge.

Early Fuji is moving rather quickly toward maturity, with many untreated fruits already in the category for long-term storage and moving quickly through maturity indices. Watch your sites carefully. We should have sampled them last week.

Empire’s same date below has ReTain applied, so take that into account when comparing to your untreated blocks. Empire are still in the immature range. The predicted date for Empire on the Ridge is Sept. 14, and this is accurate for untreated fruits for long-term CA. Since most Empire have AVG applied per buyer requirements, they are most likely five to seven days away from the ideal range for long-term CA storage for the general Grand Rapids area.

Jonagold is very immature. Our predicted harvest date is Sept. 29, which is very close to a normal average harvest date. This seems odd given the early nature of all other varieties, but our estimates are based on models that take into account the weather shortly after bloom, which was very long and drawn out this spring. It will be interesting to see what next week’s samples will show with Jonagold. For now, they are not ready.

Jonathan (Jonee) are a similar story as Jonagold. Jonathan is very immature at this time.

Apple storage parameters for different varieties

*Firmness is measured with a mechanical 11-millimeter wide probe inserted into the pared flesh of a fruit to a distance of 8 millimeters. Starch index is measured on equatorial cross section of an apple stained with iodine solution and rated using the Cornell University starch-iodine index chart for apples on a 1-8 scale (Predicting Harvest Date Window for Apples by Blanpied and Silsbey, Cornell Extension Bulletin 221.)

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