Daybreak Fuji fruit size and color in Adams County Pennsylvania on September 6, 2018. Photo: Tara Baugher, Penn State
While we haven’t had many record heat days this summer, August temperatures were still above average. High humidity trapped heat at ground level, frequently keeping nighttime temperatures above 70°F. This is the same principle that reduces frost on cloudy spring nights, while clear spring nights allow orchard temperatures to drop. Warm summer nights also increase fruit respiration, and in doing so decreases fruit sugar.
Photo 1. Honeycrisp apples ready to spot-pick in Adams County, Pennsylvania on September 4, 2018. The highly-colored fruit were mostly in the top of the tree while greener fruit were hidden by the foliage. Photo: Chris Walsh, University of Maryland
Fruit size is good, but these high temperatures have accelerated ripening, causing fruits to soften and lose starch. In the samples spot-picked this week, firmness averaged 14.1 pounds which was 2.3 pounds less than last week. Averages don’t tell the complete story, however. The fruit we tested ranged from 16 pounds to 10 pounds firmness. Clearly, the data from that small sampling show the potential variability of storage life and shelf life caused by the hot summer weather.
Starch staining patterns (Photo 2) are variable in Honeycrisp apples, and that variability was particularly evident this week. While the trees sampled did not have adequate red color to begin commercial spot-picking, the fruit had metabolized most of their starch. In watching Honeycrisp, we’ve noticed an apparent ‘final swell’ that accompanies the loss in starch. Fruit weight increased dramatically in the past week, from 195 grams to 233 grams, which was an increase of 3% a day.
Photo 2. Honeycrisp apples spot-picked at 1200 feet elevation in Adams County, Pennsylvania on September 4, 2018. These apples had about 39 percent red color, 14.4 pounds firmness and had lost most of their starch (blue stain) in the flesh. Photo: Kathy Hunt, University of Maryland
As growers wait for red color development, continued fruit growth is also leading to other physiological problems. Despite spot-picking, we noticed problems with stem-end russetting and bitter pit. What was not expected was the significant percentage of fruit with shoulder-cracks and the small percentage of soft apples with internal breakdown.
Photo 3. Honeycrisp apples are prone to a number of physiological disorders. Left apple – bitter pit; Center apples – shoulder cracking and stem end russet; Right apple – onset of internal browning. Photo: Kathy Hunt, University of Maryland
With our recent hot weather, spot picking for red color is particularly important. The Penn State Extension Honeycrisp Multiple Harvest Calculator is a nice calculator that determines potential economic returns on the value of spot picking.
While this week’s observations were taken from fruit grown on size-controlling rootstocks, check your fruit maturity. Small differences in microclimate or orchard management may make a large difference in maturation. Management practices that might hasten fruit maturity are summer PGR applications to enhance return bloom, mechanical pruning to increase red color development and the planting of new red-colored varieties.
Table 1. The following table shows data from our pre-harvest Honeycrisp apple samples evaluated in August and early September.
Honeycrisp: Central Maryland 575 feet elevation
|Date||ReTain Treatment||Diameter (inches)||Red Color (%)||Ground Color||Firmness (pounds)||Starch Pattern |
(1 – 8)
|Soluble Solids (°Brix)|
|21-Aug-18||No ReTain||3||50||Yellowish green||16.3||6.8||11.5|
|28-Aug-18||No ReTain||3.2||45||Yellowish green||16.3||7.5||13.9|
|4-Sep-18||No ReTain||Harvest completed|
|4-Sep-18||ReTain||Harvest Begin: Sep 1|
Honeycrisp: Adams County Pennsylvania 1200 feet elevation
|Date||Diameter (inches)||Red Color (%)||Ground Color||Firmness (pounds)||Starch Pattern (1 – 8)||Soluble Solids (°Brix)|
Growers began Gala harvest in the middle of August. Most growers in Maryland and Southern Pennsylvania completed picking this variety by Labor Day.
This variety was remarkably responsive to last year’s hot weather. We estimated that Daybreak Fuji were picked almost three weeks earlier in 2017 than in 2015 and 2016. Growers should be watching this variety for maturity. In Central Maryland and Adams County, PA we have noticed sun-burned Daybreak Fuji fruit are now ripening.