Apple PGRs - Shifting Harvest Window of Gala a Risk in Warmer Climates

Researchers in cooler regions have recommended the 2-pouch rate of ReTain be used to delay harvest by up to six weeks, but this was not possible in Southcentral PA in 2016.
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Updated: October 3, 2017

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Apple PGRs - Shifting Harvest Window of Gala a Risk in Warmer Climates

Buckeye Gala/M. 9. Photo: Tara Baugher, Penn State

Shifting Harvest Window of Gala a Risk in Warmer Climates

ReTain trials conducted in 2016

Trials were conducted at the Penn State Fruit Research and Extension Center in 2016 to evaluate the effect of the revised label rate of ReTain, as a single spray or a split application, to Gala apple trees on harvest maturity, yield, fruit size distribution, and fruit quality. The economic impact of the increased costs and management inputs, as well as the effects on yield, and packout were also evaluated.

In July and August, 2016, mature tall spindle ‘Buckeye Gala’/ M.9 apple trees at Penn State’s Fruit Research and Extension Center were treated as follows:

  1. One pouch per acre of ReTain (50 grams a.i./acre) at 4 weeks before anticipated harvest (WBAH);
  2. Two pouches per acre of ReTain (100 grams a.i./acre) as a split application: 4 WBAH, and 2 WBAH;
  3. Two pouches per acre ReTain at 4 WBAH;
  4. Two pouches per acre ReTain at 2 WBAH;
  5. Untreated control.

Treatments were applied to 3-tree plots by air-blast sprayer at 100 gallons per acre, with 0.05% vol./vol. Silwet L-77 organosilicone surfactant to maximize foliar absorption. The 4 WBAH sprays were made on 26 Jul at 8 pm, and the 2 WBAH sprays were made on 10 Aug 10 at 8 am. Treatments were segregated by buffer trees and arranged as a randomized complete block design with six replications.

Fruit sampling was originally scheduled to begin 4 weeks after anticipated harvest (WAH), but fruit maturity was observed to be advanced, so sampling and harvest began 1 WAH. Fruit samples from one tree per plot were collected at weekly intervals for evaluation of fruit maturity, fruit color, and growth. All fruit from two other trees per plot were selectively harvested at proper maturity and evaluated for number of picks, yield, and fruit size distribution. All fruit from harvested trees were visually graded, using USDA grading standards for fruit color and freedom from defects. A sample of 25 fruits per plot was collected during grading and held for 60 days in refrigerated storage at 1°C, then held at 20°C for several days for evaluation of fruit firmness and incidence of postharvest disorders.

Yield, fruit size distribution, packed fruit grade, and additional costs associated with treatments was recorded to evaluate economic impacts by partial budget analysis.

Results—only a slight shift in harvest window in 2016

One or two pouches of ReTain slowed starch disappearance at 1 WAH, (29 Aug) (Table 1). By the second and third sample dates, only the two-pouch rate delayed starch disappearance compared to the control. Internal ethylene concentration was already greater than 1 ppm for all treatments by 1 WAH, regardless of ReTain rate or timing (Table 2). ReTain reduced internal ethylene on 5 Sept, except for an anomalous result of no difference for 2 pouches per acre applied 4 WBAH. All double rates of ReTain had lower internal ethylene by 3 WAH (12 Sept.), but the single pouch rate was not different than the untreated control.

The primary harvest date for untreated trees was 30 Aug, while all ReTain treatments had primary harvest 3 weeks later, on 19 Sept (Table 3). Firmness and soluble solids were not different among treatments for fruit samples collected at these primary dates. Titratable acidity of fruits from the 1-pouch rate and the split application was slightly lower than that of the untreated controls. Following cold storage, fruit from the 1-pouch rate of ReTain was firmer than that of the other treatments (Table 4).

Yield, fruit number per tree and fruit size were unaffected by ReTain treatment (Table 5). Red fruit coloration was not strongly affected by treatment. The extent of blush coverage was not affected by treatment, although trends were nearly significant for the exposed side of the fruit on 31 Aug (Table 6). On this date the trend was for less red coverage on fruit from the 1-pouch rate and the 2-pouch rate applied 2 WABH. Spectral properties of the fruit are presented in Table 7. On the blushed side (exposed side) of the fruit, the untreated fruit from 30 Aug were slightly lighter. On the background (not exposed) side of the fruit, fruits from all ReTain-treated trees had slightly more chroma on 20 Sep than untreated fruit from 30 Aug.

Cumulative out-of-grade fruits from all harvest dates are summarized in Table 8. Lack of red fruit color and phytotoxicity were the two primary factors for fruit being out-of-grade. Poor color was highest for untreated controls, which likely reflects the earlier primary harvest date and picker error, more than treatment. Loss of quality was due primarily to phytotoxicity associated with treatment 2 WBAH (Figure 1). Phyto symptoms are shown in Figure 2.

ReTain treatments led to a reduction in the economic return in 2016, associated with the additional cost of treatments, without appreciable increases in yield or fruit quality (Table 9).

Discussion—possible reasons for only a 2 to 3 week harvest delay

The 2016 growing season in PA was very hot. For the period July – August, 2016, 63% of the days had daytime highs exceeding 86°F. For the period July – September, 51% of the days had daytime highs exceeding 86°F. As a result Gala fruit maturity was advanced. Some phytotoxicity was observed with all sprays, but it was worse with sprays applied 2 WBAH. We attribute this to the time of day of the applications. The earlier spray (4 WBAH) was made in the evening, as temperatures were dropping from the daytime high, while the 2 WBAH spray was made at 8 am, just before the diurnal rise in temperatures. This phyto is consistent with uptake of captan fungicide associated with the application of Silwet L77 and with the very high temperatures surrounding the spray application.

In a hot stressful season, higher rates of ReTain only delayed Gala harvest by 2-3 weeks. All treatments had starch index values appropriate for initiating harvest by 1 week after anticipated harvest. Likewise, by 3 weeks after anticipated harvest, all treatments had starch index values above 6, signaling that the commercial harvest window had closed. Yield/size/crop value were not increased in this season by the treatments. Researchers in cooler regions have recommended that the 2-pouch rate of ReTain be used to delay harvest by up to six weeks, but this was not possible in southcentral PA in 2016. We conclude that attempting to shift harvest window of Gala carries considerable risk in a warmer climate.

Acknowledgements: The authors thank the Penn State College of Agricultural Sciences Sunday Program for Fruit Production Research Fund, and Valent U.S.A. LLC, for their support of this research.


Figure 1. Red and yellow dots indicate the first and second days of ReTain application, respectively.


Figure 2. Examples of phytotoxicity symptoms on Gala fruit treated with ReTain and a surfactant, 2 weeks before anticipated harvest, Pennsylvania, 2016.

Shifting Harvest Window of Gala a Risk in Warmer Climates Tables

Table 1. Gala apple maturity by iodine starch method

Pennsylvania, 2016

DateTreatmentUnstained flesh extent (% of cut apple unstained by iodine)Corresponding Starch Index Valuez
8/29/16One pouch per acre Retain, 4 WBAH44.7b4.4
2 pouches per acre: 4 WBAH and 2 WBAH30.7c3.4
2 pouches per acre: 4 WBAH30.2c3.3
2 pouches per acre: 2 WBAH24.8c2.9
UTC65.9a5.9
p-value0
9/7/16One pouch per acre Retain, 4 WBAH74.5ab6.5
2 pouches per acre: 4 WBAH and 2 WBAH63.9bc5.8
2 pouches per acre: 4 WBAH56.7c5.3
2 pouches per acre: 2 WBAH67.8bc6.1
UTC80.4a6.9
p-value0
9/12/16One pouch per acre Retain, 4 WBAH87.5ab7.3
2 pouches per acre: 4 WBAH and 2 WBAH76.6c6.6
2 pouches per acre: 4 WBAH81.4bc6.9
2 pouches per acre: 2 WBAH80c6.8
UTC91.8a7.5
p-value0

zCorresponding starch index value from the Cornell starch iodine chart developed by Blanpied and Silsby.

Table 2. Gala fruit internal ethylene content concentration

Pennsylvania, 2016

TreatmentInternal ethylene (ppm) on date
8/29/169/5/169/12/16
One pouch per acre Retain, 4 WBAH1.51.8bc1.7a
2 pouches per acre: 4 WBAH and 2 WBAH1.21.2c0.8b
2 pouches per acre: 4 WBAH1.42.2ab1b
2 pouches per acre: 2 WBAH1.71.2c0.9b
UTC2.82.7a1.7a
p-value0.5300

Table 3. Gala fruit quality

Pennsylvania, 2016

TreatmentPrimary harvest datePressure (kg)Soluble solids (Brix)Titratable acidity (% MA)
One pouch per acre Retain, 4 WBAH9/19/167.9513.50.28bc
2 pouches per acre: 4 WBAH and 2 WBAH9/19/167.8913.40.26c
2 pouches per acre: 4 WBAH9/19/168.3713.40.31ab
2 pouches per acre: 2 WBAH9/19/168.5813.60.29abc
UTC8/30/168.3813.20.33a
p-value0.540.420.02

Table 4. Gala fruit firmness after cold storage

Pennsylvania, 2016

TreatmentPressure (kg)
One pouch per acre Retain, 4 WBAH6.9a
2 pouches per acre: 4 WBAH and 2 WBAH6.4b
2 pouches per acre: 4 WBAH6.2b
2 pouches per acre: 2 WBAH6.1b
UTC6.1b
p-value0

Table 5. Gala yield and fruit size data

Pennsylvania 2016

TreatmentYieldCountAverage Fruit Size (g)
One pouch per acre Retain, 4 WBAH22136163
2 pouches per acre: 4 WBAH and 2 WBAH24.4146171
2 pouches per acre: 4 WBAH22.3131172
2 pouches per acre: 2 WBAH26.2154170
UTC24.1149163
p-value0.60.780.77

Table 6. Effect of ReTain treatments on Gala apple blush coverage on front and background sides of apples

Pennsylvania 2016

DateTreatmentBlush Side % BlushBackground side % Blush
8/31/16One pouch per acre Retain, 4 WBAH7069.6
2 pouches per acre: 4 WBAH and 2 WBAH83.554.3
2 pouches per acre: 4 WBAH8159.2
2 pouches per acre: 2 WBAH64.784.1
UTC87.362.3
p-value0.060.61
9/20/16One pouch per acre Retain, 4 WBAH87.3not measured
2 pouches per acre: 4 WBAH and 2 WBAH84.5not measured
2 pouches per acre: 4 WBAH87.6not measured
2 pouches per acre: 2 WBAH82.7not measured
UTC90.9not measured
p-value0.86

Table 7. Effect of ReTain treatments on Gala fruit color on front and background sides of apples

Pennsylvania 2016

Blush Side

TreatmentDate harvestedLCh
One pouch per acre Retain, 4 WBAH20-Sep42.1b31.726.3
2 pouches per acre: 4 WBAH and 2 WBAH20-Sep41.2b32.426.3
2 pouches per acre: 4 WBAH20-Sep42.6b31.426.2
2 pouches per acre: 2 WBAH20-Sep42.4b33.927.2
UTC31-Aug45.4a31.327.5
p-value0.010.250.56

Background side

TreatmentDate harvestedLCh
One pouch per acre Retain, 4 WBAH20-Sep60.329.8a48.3
2 pouches per acre: 4 WBAH and 2 WBAH20-Sep60.129.7a50.6
2 pouches per acre: 4 WBAH20-Sep60.428.6a51.8
2 pouches per acre: 2 WBAH20-Sep62.729.2a57.6
UTC31-Aug64.725.7b60.5
p-value0.170.010.11

Table 8. Effect of ReTain treatments on culled fruit prevalence of Gala apples

Pennsylvania 2016

TreatmentPoor color*Phytotoxicity*Cracking*Blemish*
One pouch per acre Retain, 4 WBAH1.2c9.1b7.20.8
2 pouches per acre: 4 WBAH and 2 WBAH2bc20.6a42
2 pouches per acre: 4 WBAH1.8bc7.3b6.41.5
2 pouches per acre: 2 WBAH5.3ab28.6a3.41.5
UTC6.9a0b0.21.8
p-value0.0200.20.58

*Percentage of affected fruit.

Table 9. Effect of ReTain treatments on economic outcomes of Gala apples

Pennsylvania, 2016.

TreatmentCrop value ($ per acre)Cost of ReTain application ($ per acre)Crop value minus cost of application ($ per acre)
One pouch per acre Retain, 4 WBAH1,324.68290.51034.18b
2 pouches per acre: 4 WBAH and 2 WBAH1,487.36586.81900.55b
2 pouches per acre: 4 WBAH1,388.59563.57825.02b
2 pouches per acre: 2 WBAH1,609.37563.571039.99b
UTC1,458.310.001458.31a
p-value0.560.01

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