General apple harvest comments

Southwest Michigan growers have been actively harvesting Gala, Empire and Jonathan. Honeycrisp is being spot picked. Some Golden Delicious are being harvested for processing.

Woolly apple aphid colonies are becoming more common in some orchards. Their honeydew can spoil apple finish and annoy harvesting crews. If management is needed, Closer SC is an excellent aphid product with a short, seven-day preharvest interval.

Brown marmorated stink bug (BMSB) numbers are still increasing. Trap catches for oriental fruit moth, codling moth and obliquebanded leafroller are still significant in some orchards, indicating some orchards need continued protection. Several products are available that are effective on moths as well as BMSB, but pay close attention to preharvest intervals.

Fruit are generally clean, however sooty blotch and flyspeck disease symptoms are common on unprotected fruit in abandoned orchards, indicating fungicide protection has been needed. Bitter rot continues to be a problem in varieties such as Honeycrisp, Empire and Golden Delicious. Fungicide options close to harvest include Captan and Merivon. Take special care should to keep infected apples out of the harvest bin to avoid infecting other fruit.

Samples collected for this report are from the central Berrien County region, targeting more mature fruit on the outside of the tree canopy. Fruit in the interior of the tree will be less advanced than shown here. Sites with heavier soils and greater crop loads will generally be less mature.

The predicted harvest dates are based on temperatures from spring to 30 days after bloom and do not take into account summer temperatures which can push development earlier or later than predicted. Hot weather over the past 30 days has stimulated internal ethylene levels in apple fruit and pushed along apple development.

Individual variety results

Gala maturity readings are very similar to last week. Harvest is moving quickly in many orchards. Starch readings indicate some orchards have fruit that are internally mature (3 or above), but still with excellent firmness that will allow harvest to be delayed for better fruit size and sugar (brix). Rains over the past week have helped fruit sizing. Skin color is generally good to very good, with some of the newer red strains nearly solid red. The predicted harvest date for southwest Michigan in 2020 is Sept. 11.

Honeycrisp starch conversion is 6.1, a sizable jump over last week’s average of 3.5 with a target mature starch index of 3.5 for this variety. Starch readings are quite variable from fruit to fruit at individual orchards, ranging from 1 to 7, indicating the need for spot picking. The current average firmness of 15.4 is a significant drop from last week’s average of 17.1. The general guideline is 17 pounds for best long-term controlled atmosphere (CA) storage. The predicted peak harvest date is Sept. 15 for central Berrien County.

Empire was sampled for the second week. Firmness is still holding at 20 pounds, and the starch conversion index is likewise holding at about 2. The target starch test for mature apples for apples destined for fresh market or fresh apple slices is 3.5 with a minimum firmness of 16 for long-term CA storage. Predicted harvest dates for fresh market for central Berrien County is Sept. 21, which seems to be about on track.

Jonathan was sampled for the second week, with current average firmness of 18.9 pounds and starch conversion of 3.0, very similar to last week. The target starch test for mature apples for apples destined for fresh market or fresh apple slices is 3.5 with a minimum firmness of 16 for long-term CA storage. Predicted harvest dates for fresh market for central Berrien County is Sept. 24, which seems to be in line with the current observed apple maturity.

Jonagold was sampled for the second week. Starch conversion this week is averaging 3.2, with 3.5 as the target for mature for this variety. Fruit firmness this week averaged 18.2 pounds, with the general guideline of a minimum of 17 pounds firmness for best long-term CA storage. The predicted peak harvest date is Sept. 24 for central Berrien County.

Early Fuji starch conversion this week is averaging 5.0, with 3.0 as the target for mature for this variety. Fruit firmness this week averaged 17.8 pounds, with the general guideline of a minimum of 18 pounds firmness for best long-term CA storage. The predicted peak harvest date is Sept. 6 for central Berrien County. This variety is maintaining very good eating quality.

Golden Delicious was sampled for the first time. Starch conversion this week is averaging 1.3, with 3.0 as the target for mature for this variety. Fruit firmness this week averaged 18.4 pounds, with the general guideline of a minimum of 17 pounds firmness for best long-term CA storage. The predicted peak harvest date is Sept. 27 for central Berrien County.

Red Delicious was sampled for the first time. Starch conversion this week is averaging 2.1, with 2.5 as the target for mature for this variety. Fruit firmness this week averaged 18.7 pounds, with the general guideline of a minimum of 17 pounds firmness for best long-term CA storage. The predicted peak harvest date is Sept. 30 for central Berrien County.

*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.