MSU Extension

Hot harvest concerns

The predicted hot weather for later this week will advance apple maturity, including increased tendency for pre-harvest drop, increasing the need for effective stop-drop and ripening inhibitor treatments. It’s going to be difficult to get the latent heat out of apples over the next several days with daytime highs predicted in the upper 80s and 90s, and nighttime temperatures in the 60s. Read “Hot, hot apple harvest concerns” by Michigan State University Extension for considerations to this unusual situation.

Apple storage considerations

The following information on storing apples is taken from Randy Beaudry’s 2016 article, “Apple storage advice for 2016 – a warm year at harvest,” and is applicable for this harvest season.

“One important consideration is the temperature of the fruit going into controlled atmosphere (CA) storage. Gala and other fruit harvested in the early days of fall are now going in warm, so extra attention needs to be paid to temperature monitoring.

“In terms of temperature prior to CA storage, we usually like to see the temperatures of the warmest fruit at about 45 to 50 degrees Fahrenheit, but lower temperatures are better to be sure. Temperature control is your number one friend when it comes to preserving apple fruit quality.

“Another reason temperature control is important in warm years is that the fruit coming in at high temperatures respire much faster than cool fruit, leading to a rapid build-up of CO₂ (carbon dioxide) in the storage environment. In a room with a closed (not sealed) door, CO₂ levels can reach 5 percent overnight! For CO₂-sensitive varieties (e.g., Honeycrisp, Empire, Jonathan, McIntosh), this can be disastrous. For these varieties, Michigan State University Extension recommends putting a half- or a quarter-skid of lime in the room during loading, especially if the fruit are coming in warm. CO₂ scrubbing may also be an option.

“Cooling fruit is important, but even warm fruit are responsive to 1-MCP. For most varieties, there is no reason to delay the application of 1-MCP. Our work has shown that 1-MCP is similarly effective from 32 to 70 F, and keep in mind multiple applications are just fine. There is no harm to treating the same fruit twice if room loading is stretching out due to waiting on color (also a problem some warm years) or labor or weather issues.

“With regard to treating fruit at higher temperatures, an exception might include Golden Delicious, which, during warm harvest seasons, seems to be susceptible to a surface discoloration when treated with 1-MCP while still warm. I’ve not seen this disorder on Michigan fruit, but I have on Ohio Goldens in 2012.”

General apple harvest comments

We are seeing upsurges in brown marmorated stink bug activity, particularly near corn and soybean fields that have either been harvested or are under stress. Warm temperatures stimulate movement of this insect to feed sources and potential overwintering sites such as buildings.

Most apple varieties can be stored at temperatures near 32 degrees Fahrenheit, but Honeycrisp is prone to chilling injury when stored at temperatures below 36 F. Honeycrisp and other chilling-sensitive apples should be stored at 37 F.

Data for last and the current weeks are given in the following tables are based on samples collected from commercial orchards in the central Berrien County area. Firmness and starch ranges are the observed low and high mean values.

Last week:

This week:

Individual variety results

No new samples of Gala were tested this week, as most area blocks have been harvested or nearly so. Last week’s report showed all blocks had starch conversions readings testing internally mature (3 or above) with the overall average of 5.1.

Honeycrisp harvest is moving rapidly in the area. Starch conversion is nearly complete, averaging 7.8 compared to 6.9 of last week (3.5 is considered mature). Firmness and brix are nearly the same as last week, now averaging 14.2 and 13.6, respectively. All sites tested below the ideal of 16 for mid-term controlled atmosphere (CA) storage. The predicted peak harvest date is Sept. 4 for central Berrien County for 2017, quite a bit ahead of the normal date of Sept. 15.

Precondition Honeycrisp fruit between 50 and 68 degrees Fahrenheit for five to seven days before refrigeration to help avoid storage disorder problems. Honeycrisp apples should be stored at 37 F. The combination of bitter pit and lenticel rot in combination have resulted in significant culling of Honeycrisp in some orchards with large fruit due to low crops caused by spring frosts.

Jonagold reached internal maturity sufficient for harvesting at least one week ahead of the target harvest date for central Berrien County of Sept. 15. This week’s average starch index is 7.3, compared to 6.3 for last week. The target starch index for fruit destined for fresh market is at least 3.5. Current firmness of 15.8 pounds is about the same as last week, and is in the recommended mid-term CA storage window range.

Jonathan maturity is moving steadily with firmness of 17.0 pounds, still above the borderline of 16 between long and mid-term CA storage. The current starch test is averaging 5.6, compared to last week’s 4.0 and above the 3.5 point, which is considered mature for successful CA storage. Many of the area Jonathan blocks have been picked. The predicted peak harvest date for central Berrien County is Sept. 15, which seems to be about right.

Empire starch conversion reading this week is averaging 4.4 compared to 3.9 last week, and well above the 3.5 point considered mature. Fruit firmness averages continue to hold at an average of 17 pounds. The predicted peak harvest date is Sept. 10 for fresh market for central Berrien County, which matches what we are seeing in the field. Brix is averaging 13, about the same as last week. Area growers are busy harvesting Empires this week.

Golden Delicious were tested for the third time with firmness this week averaging 17.1, about the same as last week. Starch conversion continues to move significantly, with a current average of 4.4 compared to last week’s 3.6 and 1.4 for the week before, with 3.0 considered to be mature. The area brix average moved to 14.2 this week compared to last week’s 12.7.

Harvesting of area Golden Delicious has renewed this week, but many blocks have not yet been touched by harvesters. Golden Delicious are showing no blush up to 30 percent orange/pink on green background. The central Berrien County predicted peach harvest date is Sept. 19. Long-term CA storage is best when fruit are internally mature and firmness is 17 pounds or greater.

Red Delicious were sampled from 10 sites or strains this week, with firmness testing at 17.6 pounds and starch conversion now at 3.0. A starch reading of 3.5 is consider sufficiently mature for harvesting. The predicted peak harvest date for Red Delicious in central Berrien County for 2017 is Sept. 22. Internal apple flesh water soaking is starting to show up in more mature blocks.

Predicted peak fresh market apple harvest dates

The normal and estimated 2017 peak harvest dates for apple varieties in southwest Michigan table is included here, as general guidelines. Predicted harvest dates for early season apple varieties are 10 to 15 days ahead of normal due to warm temperatures in the month following bloom. Light crop and earlier dry conditions have also advanced maturity. These dates are an estimate and will be affected by the apple strain, rootstock, crop load, fertility, soil type and other factors including current weather.

*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.