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Mitigating WA 38 greasiness

Printable Handout – Station 2 Mitigating WA 38 greasiness

Problem

Peel greasiness can develop at any time, both before and throughout the cold chain, on many apple cultivars, including WA 38. Besides diminished appearance, greasiness or, potentially, mitigation using high amounts of fruit finish aids (waxes and/or shellac) can be associated with off-flavors.

Project Goal

1.Further define harvest maturity guidelines limiting the greasiness of WA 38 in the cold chain.

2.Establish ethylene mitigation protocols that reduce WA 38 greasiness for both conventional and organic production.

Background

Map of the state of Washington with 5 experimental locations highlighted: Wenatchee, Quincy, Royal City, Mattawa, Zillah
Figure 1. Study sites.

 

Cross-section of six apples at different stages of maturity and stained with iodine. The apples are arranged in a line from one to six showing different stages of maturity, which is characterized by the amount of starch in the fruit. A less-ripe fruit will contain more starch and turn blue when stained with iodine; a ripe fruit will have very little starch and will not stain. The ripening begins at the core of the fruit and extends outwards,
Figure 2. Cosmic Crisp cv. WA 38 Starch Scale

Harvest maturity and skin greasiness

Starch Index populations at different timepoints pre- and postharvest.

Six graphs with starch index (1-6) on the x-axis and density on the y-axis, Data is from two sites, Mattawa and Quincy. Both sites have one graph for 2023, one for 2024, and one figure that includes weekly data from zero to three weeks post harvest. We can see the starch index increasing with time after harvest, meaning that the fruit continues to ripen in storage.
Figure 3. Data from Mattawa and Quincy looking at fruit density at harvest and one week after harvest for the years 2023 and 2024.
Data for 2022 (top two figures) and 2023 (bottom two figures) for Quincy site. Starch index is on x-axis, and fruit count on y-axis, Left two graphs are AIR - 2 months; right two are CA - 2 months.
Figure 4. Data for 2022 and 2023 for Quincy site.
Figure shows two graphs, one of the preharvest data for 2023 and one for the preharvest data for 2024. Weeks before/after harvest is on x-axis, and starch index is on y-axis.
Figure 5. Preharvest and post-harvest data for 2023 and 2024

PGRs to Reduce Greasiness

Retain®

2022: No effect on greasiness incidence, but yes in severity, up to 4 months   into storage (H1+1d)
Maturity: delayed starch degradation (H2), reduced ethylene production up  to   4m into storage in H1.

2023: Reduced greasiness (incidence and severity) at harvest and 4m +1d   68oF
Maturity: delayed starch degradation (21 DBH), no consistent effect   over C2H4.

Table 1. Retain®

Year Treatment Material/a.i. Rate Timing Others
2022 1 Untreated control (UTC) NA NA Orchard location: Zillah, WA
Sylcoat (0.1% OSi) added to Retain® applications.
Two harvests: At the time of UTC (commercial), and 1 week later.
2 AVG (ReTain®) Full rate
(24 oz/acre) 		7 DBH
3 ReTain® Half-rate
(12 oz/acre)		 7 DBH
2023 1 Untreated control (UTC) NA NA
2 AVG (ReTain®) Full rate 21 DBH
3 ReTain® Full rate 14 DBH
4 ReTain® Full rate 7 DBH
2024 1 Untreated control (UTC) NA NA
2 AVG (ReTain®) Full rate 14 DBH
3 ReTain® Double rate 14 DBH
4 ReTain® Double rate 7 DBH

1-MCP (HarvistaTM, SmartFreshTM)

2022: No consistent effect over greasiness (incidence and severity).
Maturity: significantly delayed softening, reduced ethylene production (mostly SF).

2023:  No effect over greasiness.
Maturity: significantly delayed softening, reduced ethylene production (mostly SF).

Table 2. 1-MCP (HarvistaTM, SmartFreshTM)

Year Treatment Material/a.i. Rate Timing Others
2022 & 2023 1 UTC NA NA Orchard location: Royal City, WA
Two harvests: At the time of UTC (commercial), and 1 week later.
Only harvest 1 for SF treats.
2 1-MCP (HarvistaTM 1.3 SC) (1x) Full dose 14 DBH
3 HarvistaTM (2x) Full dose 14 & 7 DBH
4 UTC plus 1-MCP (SmartFreshTM; SF) 100 ppm At harvest
5 HarvistaTM 1x plus SF T2 plus SF (100 ppm) At harvest
2024 1 UTC NA NA
2 UTC plus 1-MCP (SmartFreshTM; SF) At 100 ppm At harvest

Final Remarks

  • Maturity progression varies between sites. The starch degrades at different rates in different years.
  • Fruit greasiness appears to be more related to fruit maturity and perhaps seasonal weather than just tree age.
  • Overall, fruit from the 2022 season had lower greasiness incidence and severity than that of 2023 and 2024 seasons.

cooler weather > greasiness

  • Slight less starch degradation in CA (less than 0.5 points)
  • More greasiness during ‘shelf-life’

Funding

Washington Tree Fruit Research Commission

Contacts

Carolina Torres, PhD.
ctorres@wsu.edu
Associate Professor
Endowed Chair in Tree Fruit Postharvest Systems
Tree Fruit and Extension Center
Washington  State University
Wenatchee, WA

Washington State University