Retractable Netting and Evaporative Cooling for Sunburn Control and Increasing Red Color for ‘Honeycrisp’ Apple

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Noah Willsea Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Victor Blanco Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Orlando Howe Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Thiago Campbell Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Erica Casagrande Biasuz Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Lee Kalcsits Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Abstract

Protective netting and evaporative cooling are commonly used for sunburn protection in apple (Malus domestica Borkh.) orchards in semiarid environments such as central Washington state. Sunburn is caused by a combination of solar radiation and heat, which can cause significant economic losses. Although protective netting and evaporative cooling can be effective for preventing apple sunburn, netting can also introduce new risks, including red color development on the fruit surface. This study evaluated whether retracting netting before harvest improves red color development and/or changes sunburn risk compared with leaving netting in place until after harvest. An experiment was conducted that compared three netting treatments: 1) netting from June until harvest, 2) netting retracted 10 d before harvest, and 3) no netting all season combined with the presence or absence of evaporative cooling. Fruit was harvested and assessed for sunburn incidence and external quality characteristics immediately after harvest. In retracted netting treatments, red color was higher when netting was retracted compared with the nonretracted controls, and sunburn risk did not increase with netting retraction. Evaporative cooling reduced sunburn incidence. Retractable netting can be used to minimize the loss of fruit to sunburn while allowing a full light environment that promotes red color near harvest. There is no inherent increase in sunburn risk from netting retraction, and the proportion of fruit with red color improved.

Light interception is an important factor affecting apple tree productivity and fruit quality (Musacchi and Serra 2018). Direct sunlight is specifically required for the development of red color on the apple surface. Large, vigorous trees have many fruit located in the inner canopy that can sometimes have poor red color due to the limited sunlight. The use of dwarfing rootstocks and new training systems has led to high-density orchards, with lower vigor trees, that improve light penetration into the canopy and increase the number of fruits exposed to full sunlight (Wagenmakers and Callesen 1995). Consequently, these orchards also face high sunburn pressure because of the increase in direct light exposure (Racskó et al. 2005).

Poor red color and sunburn are among the leading causes of culls in Washington State, which is a hot, semiarid apple production region (Brunner et al. 2004). Sunburn occurs in many fruits and vegetables (Barber and Sharpe 1971) when elevated temperatures and excess light damage sensitive horticultural crops. Sunburn will produce brown or black lesions on the fruit surface, affecting fruit marketability. It is an especially consequential disorder for apple (Munné-Bosch and Vincent 2019), with sunburn incidence reaching 10% or greater in some regions (Schrader et al. 2008). As such, hot summer temperatures can be challenging for apple production. Air temperatures exceeding 35 °C increase the risk for sunburn development, causing losses in both yield and marketable fruit.

Hot temperatures also affect fruit quality such as red color development in apples. Specifically, warm night temperatures can limit red color development before harvest. Red fruit color is one of the most important quality standards that determine grade and marketability of apples (Musacchi and Serra 2018), and it is a key focus on grower efforts to increase fruit quality. In some years, high temperatures near harvest can limit red color development for earlier developing cultivars and cultivars with poor coloring. In these situations, it is difficult to increase red color of fruit and can lead to issues with over-maturity because fruit might be left on the tree past optimal physiological maturity to achieve sufficient color.

Mitigation practices can reduce sunburn, but these practices can also sometimes limit red color development, so the selection of one practice over the others should be based on cultivar value, location, water availability, and overall risk of sunburn occurring (Willsea et al. 2023). The main strategies include water-based cooling, netting, reflective sprays, and ultraviolet light-blocking compounds (Evans et al. 1995; Gindaba and Wand 2008; Glenn et al. 2002; Mupambi et al. 2018). These strategies either reduce incoming solar radiation that reaches the fruit surface or provides fruit cooling through heat removal.

Water-based cooling actively cools the fruit surface or indirectly cools fruit by reducing air temperatures surrounding it. These strategies include evaporative cooling of fruit through cycling water applications on and off, convective cooling of the air around the fruit, and hydrocooling the fruit continuously during the day. These strategies increase water use and may not be suitable in areas where water is scarce. When low-volume cooling systems are used with appropriate cycling times, low amounts of water will reach the soil, and most will evaporate from the canopy or groundcover.

Netting, sprays, and fruit bagging reduce solar radiation reaching the fruit surface, keeping fruit closer to ambient temperature. The use of netting is essential in some areas for protection from hail and has also been rapidly adopted for protection from sunburn in semiarid regions with temperatures that exceed 35 °C during the summer (Iglesias and Alegre 2006; Mupambi et al. 2018). However, netting limits incoming light conditions and can limit red color development in some cases (Serra et al. 2020). A balance between protecting fruit from high summer temperatures and providing adequate light conditions that promote the development of fruit color can be reached by using the most appropriate within a large range of netting colors, weave patterns, and material available, all of which can contribute to factors that affect both quantity and quality of incoming light (Mupambi et al. 2018; Shahak 2012). Although all these strategies previously described are used to mitigate sunburn, adapting, or combining these strategies may be required to control high temperatures and maximize light penetration into the canopy to produce the highest commercial quality fruit.

The objective of this study was 1) to test whether netting retraction near harvest can provide protection during the heat of the summer while not limiting color development if left on until after harvest and 2) to assess the effects of the use of netting alone or combined with evaporative cooling on sunburn incidence and red color development. The information provided here will guide growers when choosing sunburn protection strategies in high-value apple cultivars.

Materials and Methods

Experimental design.

This experiment was conducted at the Washington State University Sunrise experimental orchard in Rock Island, WA, USA (47°18′35.6″N, 120°03′59.5″W) in a top-worked Firestorm® Honeycrisp orchard that was regrafted in 2016 with M9-T337 rootstock and a ‘Granny Smith’ interstem planted to a spacing of 0.9 m between trees and 3.6 m between rows. The site is characterized by shallow sandy loam soil. Trees were trained as a three-axis multileader fruiting wall with leaders that are 30 cm apart. The experimental design was a split plot design with evaporative cooling as the main plot and netting as a secondary plot with six treatments. There were three replicates for each treatment consisting of a group of 12 trees. Three inner trees with uniform crop load were selected as sample trees for each replicate.

There were six treatments, which resulted of the combination of two evaporative cooling regimes with three netting scenarios. The two evaporative cooling regimes were either trees receiving evaporative cooling from June 15 until harvest or no evaporative cooling. Evaporative cooling was provided with a battery-powered automatic solenoid system attached to a 100-W solar panel that was opened when air temperatures reached 30 °C. Nelson R10 sprinklers (Nelson Irrigation, Walla Walla, WA, USA) were set up at the corner of each plot with overlap of wetting from each sprinkler to the inside most part of the plot. When on, the system was set to cycle on and off every 15 min.

The three netting scenarios consisted of no netting all season, netting retracted 10 d before harvest, or netting left on until after harvest (Table 1). Netting was deployed in early June using a custom-built retracted netting system (Fig. 1). White nets made of woven polyethylene with 20% light interception provided by Extenday (Union Gap, WA, USA) were draped over single rows by attaching three wires to the trellis system, one 50 cm above the canopy and two wires placed 75 cm from the center of the row. Netting panels were then clipped onto the wires with a series of carabiners, which allow for retraction from the ground. Once the net was deployed, the two sides of the net were attached to the bottom wire using bungee cords to avoid netting movement during windy conditions. Netting was retracted for those treatments on 18 Aug 2021 and on 29 Aug 2022. Fruit was harvested on 28 Aug 2021 and 8 Sep 2022.

Table 1.

Mean fruit weight, red color coverage, and sunburn of ‘Honeycrisp’ apple fruit with netting applied all season until harvest, netting applied all season and then retracted 10 d before harvest, or no netting used all season (Factor A) or with evaporative cooling (EC) or not (Factor B) in 2021.

Table 1.
Fig. 1.
Fig. 1.

Guide wires attached to the trellis system which support the nets as well as the evaporative cooling system running during a hot afternoon (left). The setup of one replication plot before retraction over individual rows of 12 trees (right).

Citation: HortScience 58, 11; 10.21273/HORTSCI17339-23

Measurements.

On the day of retraction, thermocouples were taped with clear tape to the surface of four fruit on one tree per replicate to measure fruit surface temperature. The fruit selected were southwest facing and not shaded by leaves or branches. The thermocouples were connected to a four-channel K-type thermometer SD Logger (Model 88598, accuracy 0.1; Manufacturer AZ Instrument Corp., Taichung, Taiwan, China) that recorded temperatures every 15 min. Fruit surface temperatures were recorded for 14 d. Data were then downloaded from the dataloggers and matched with environmental conditions that were acquired from the WSU AgWeatherNetwork equipped with a temperature probe (Campbell Scientific model 107; Campbell Scientific, Logan, UT, USA), a wind speed sensor (model 014A Met One, Campbell Scientific), and a Pyranometer (model CS300, Campbell Scientific). The average daily maximum air temperature during the retraction period was 28.7 °C and 33.0 °C in 2021 and 2022, respectively.

Fruit quality was assessed for each treatment at harvest. In 2021, ∼100 fruit were harvested from the upper canopy area of each replicate to assess sunburn incidence and fruit color development. In 2022, because of lower crop loads, two representative trees per replicate were entirely picked in a single harvest time. After harvest, fruit was run through an AWETA sorting line (Nootdorp, the Netherlands) that measured fruit weight and red color coverage using internal commercially available algorithms. Sunburn incidence and severity were hand graded for each fruit using a 6-point scale adapted from Willsea et al. (2023). Fruit over a score of SB2 were considered culls.

Statistical analysis.

Statistical analysis was performed using RStudio. Significant differences for fruit quality data were determined using an analysis of variance test and a Tukey honestly significant difference test to delineate when differences among treatments were significant (α = 0.05). Where interactions were not significant (α = 0.05), main effects were presented instead.

Results and Discussion

Fruit surface temperature.

Fruit surface temperatures never exceeded 40 °C in 2021 but frequently exceeded it in 2022. The mean daily maximum fruit surface temperatures for trees that were netted were 2.5 °C (± 0.2 °C) cooler than those from trees without netting (Fig. 2). Evaporative cooling was only applied on two of 14 recorded days in 2021 during the retraction period. In contrast with 2021, evaporative cooling was used for 14 out of 17 of the recorded days in 2022. For days when evaporative cooling was applied in 2022, fruit protected by evaporative cooling were 2.7 °C (± 0.9 °C) cooler than those without evaporative cooling (Fig. 3). Netted fruit was also cooler in 2022. Fruit under netting had 0.7 °C (± 1.1 °C) cooler maximum temperature than the treatment without nets.

Fig. 2.
Fig. 2.

Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature and three different netting treatments (N = 3) (nets retracted 10 d before harvest, nets deployed until harvest, and no nets all year).

Citation: HortScience 58, 11; 10.21273/HORTSCI17339-23

Fig. 3.
Fig. 3.

Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature, treatments with evaporative cooling, and treatments without evaporative cooling (N = 3).

Citation: HortScience 58, 11; 10.21273/HORTSCI17339-23

There have not been any previous studies that look at the combination of evaporative cooling and netting. However, Gindaba and Wand (2005) found that on hot days, netting reduced fruit surface temperatures by a greater amount than evaporative cooling compared with the unprotected control in a South African orchard. Similarly, Reig et al. (2019) reported that, on average, netting reduced fruit surface temperature more than evaporative cooling compared with the unprotected control in an experiment conducted in New York State. In those studies, however, evaporative cooling was used more extensively during the middle of the growing season rather than near harvest due to environmental conditions. Hengari et al. (2014) reported that fruit was more susceptible to sunburn near maturity due to inactive lenticels and lower heat dissipation during chlorophyll degradation. This may indicate an increased importance for the role and effectiveness of evaporative cooling on hot days near harvest.

In 2022, the maximum daily fruit surface temperature for fruit where netting was retracted before harvest was 2.0 ± 1.0 °C higher than fruit from trees without netting all year. This result was different from 2021 and may be related to the placement of fruit available for measurements on trees with lower crop loads in 2022, which may have limited the ability to measure fully exposed fruit. Even before retraction, a period where the two treatments had been the same all year, fruit surface temperatures for fruit from trees that had netting retracted were 1.7 °C greater than fruit from trees where netting was not retracted. There is consistent agreement in previous research that south and west sides of the canopy are at risk for solar injury in the northern hemisphere. Khemira et al. (1993) reported that the average sunlight interception during the afternoon when air temperatures are the highest is frequently greater in the south and west sides of the canopy than the north and east. Results from Racskó et al. (2005, 2009) concur that fruit located on the western side of the canopy and closer to the top are much more at risk of sunburn in the northern hemisphere.

Fruit surface temperatures neared the reported thresholds for sunburn browning development (Racskó and Schrader 2012) during the 2-week period before harvest. Netted fruit remained well below that of unnetted fruit, but overall, severe sunburn remained below what would have been expected for fully exposed fruit. These results support the need for future research in the poorly understood area of apple’s acquisition of thermotolerance based on previous exposure. This research may also point to inconsistencies in correlating fruit surface temperatures to sunburn values (Waite et al. 2023). Kalcsits et al. (2017) and Mupambi et al. (2018) reported high levels of sunburn even with fruit that only had recorded maximum fruit surface temperatures of 41 °C and 40 °C, respectively. These findings exemplify typical inconsistencies between theoretical thresholds characterized by Racskó and Schrader (2012) and the actual in-orchard temperatures. These new findings of year-to-year differences of fruit surface temperature responses and corresponding sunburn damage levels agree with Morales-Quintana et al.’s (2020) conclusion that apple fruits’ physiological responses to heat need to be more closely studied.

Sunburn.

Sunburn incidence, indicated by graded classes other than SB0, was higher in 2021 (∼33%) than 2022 (∼19%) (Tables 2 and 3). In 2021, both netting retraction and full netting treatments reduced sunburn incidence by ∼9% (P = 0.0196) compared with the unnetted control. There was no significant difference in sunburn incidence between the retracted and fully netted treatments with mean sunburn incidences of 31% and 29%, respectively. In 2022, the total sunburn incidence follows trends observed in 2021 but was not significantly different (P = 0.1617). Total sunburn incidence in 2022 for unnetted, retracted, and fully netted treatments were 25%, 19%, and 14%, respectively.

Table 2.

Mean fruit weight, red color coverage, and sunburn of ‘Honeycrisp’ apple fruit with netting applied all season until harvest, netting applied all season and then retracted 10 d before harvest, or no netting used all season (Factor A) or with evaporative cooling (EC) or not (Factor B) in 2022.

Table 2.
Table 3.

Mean proportions of ‘Honeycrisp’ fruit belonging to five red color coverage classes (0% to 20%, 20% to 40%, 40% to 60%, 60% to 80%, and 80% to 100%) with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied in 2021.

Table 3.

Netting retraction before harvest has the potential for improving red color from increasing incoming solar radiation into the canopy at a critical time for color development. Importantly, retraction did not significantly increase either the total or severe sunburn incidence. Taking both years together, total sunburn incidence was 25% for retracted treatments and 21% for unretracted treatments (P = 0.4567). Mean severe sunburn incidence, consisting of fruit with either SB3 or SB4 classes of sunburn, did not differ among treatments and was 3% for retracted treatments and 2.3% for fully netted treatments (Fig. 4; P = 0.7230). This indicates that for years like 2021 and 2022, retraction of netting can be safely performed before harvest without increasing sunburn risk. Even though air temperatures reached a maximum of 38 °C during the retraction period in 2022, and the hottest fruit had recorded fruit surface temperatures of 48 °C on the hottest day, which would put the fruit above the threshold temperature for sunburn browning according to Schrader et al. (2008), there were no significant increases in sunburn browning when nets were retracted. However, fruit were cooler. Fruit under netted treatments were ∼3 °C cooler than fruit without netting. After retraction, previously netted fruit experienced maximum fruit surface temperatures equal to or greater than fruit without netting all year (depending on the year) yet did not result in greater sunburn incidence than any other treatment.

Fig. 4.
Fig. 4.

Mean proportions of total fruit (N = 3) with sunburn exceeding SB2 based on the scale developed by Schrader et al. (2004), which would result in cullage in a commercial setting in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied. Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

Citation: HortScience 58, 11; 10.21273/HORTSCI17339-23

Netting was an effective tool to decrease the economically important levels of severe sunburn. The treatments without netting had more than double the amount of fruit classified as either SB3 or SB4 than those with netting (∼7% vs. ∼3%, P < 0.0001). This follows similar observations for many previous studies that suggest netting as a tool for sunburn mitigation (Gindaba and Wand 2008; Iglesias and Alegre 2006; Kalcsits et al. 2017; Mupambi et al. 2018). Evaporative cooling was also effective for decreasing severe sunburn. Fruit classified as either SB3 or SB4 was 3.2% when evaporative cooling was used vs. 5% without cooling (P = 0.0187). However, this effect was stronger in 2021 than 2022. Severe sunburn incidence was 1.3% when evaporative cooling was used in 2021 compared with 3.7% without cooling (P = 0.0171). Sunburn incidence was higher in 2022, but evaporative cooling was not significantly different between treatments. These results are consistent with previous research suggesting that evaporative cooling can be effective for sunburn mitigation (Evans et al. 1995; Gindaba and Wand 2005; Van den Dool 2006). However, the efficacy of evaporative cooling is dependent on environmental conditions, and total sunburn reduction may vary by year. There was no interaction between either main effect, which means that neither treatment increased nor decreased the efficacy of the other. Although stacking multiple mitigation strategies may be useful or even necessary in the future based on climate projections (Pruett et al. 2021), further work is needed to discern the additive value from the combination of these strategies.

Fruit quality.

Fruit under the evaporative cooling treatment were significantly larger than those without evaporative cooling in 2021. Mean fruit weight was 284 g when evaporative cooling was used compared with 259 g when it was not used (Tables 2 and 3; P = 0.0165). However, these differences were not observed in 2022, when the mean fruit weight was 235 g and was not different among treatments. The differences in the effect of evaporative cooling between the 2 years could have been caused by the difference in early summer temperatures between 2021 and 2022. In 2021, daily temperatures surpassed the threshold (30 °C) for starting evaporative cooling nearly every day from May through harvest except the retraction period. This additional water may have incidentally increased fruit size in those treatments, or the cooling effect of water on leaves may increase the photosynthetic rate as suggested by Gindaba and Wand (2005). The results of larger fruit under evaporative cooling were also reported by Gindaba and Wand (2005), Iglesias et al. (2002), and Wand et al. (2020). Meanwhile, in 2022, there were a greater number of days, especially in the early season, where evaporative cooling was not used (data not shown), possibly limiting the effect of evaporative cooling on fruit growth.

All other fruit quality characteristics were unaffected by netting or evaporative cooling treatments. Among treatments, there was no significant difference in the total average red blush area (P = 0.0850). Unnetted treatments and treatments with nets retracted had similar red color coverage averages with 39% and 42%, respectively, whereas the red color coverage of treatments with nets left until harvest was 33%. However, the proportions of fruit with different red color coverages were affected by treatment. The proportion of fruit that qualify for Washington Extra Fancy (fruit with >33% blush area) was greater from trees where netting was retracted before harvest (P = 0.0293; Fig. 5). The proportion of fruit meeting this standard for red color was 47%, 57%, and 51% for unretracted, retracted, and unnetted treatments, respectively. Furthermore, when netting was retracted, there were lower proportions of unmarketable fruit with poor red color (0% to 20% blush area) (Table 4). When nets were retracted, only 34% of fruit had poor red color, whereas when nets were left until harvest, 46% of fruit had poor red color (P = 0.0261). Netting retraction, as performed in these experiments was used to maximize this amount of sunlight reaching the fruit surface. Arakawa (1988), Saure (1990), and Siegelman and Hendricks (1958) determined that sunlight is essential for the production significant anthocyanin concentrations in the apple skin. Bagging experiments have clearly demonstrated the importance of light on the development of red color (Feng et al. 2014). The effect of netting retraction near harvest may be similar to the effects reported by Lugaresi et al. (2022) when using late summer pruning to increase the amount of light reaching the fruit surface.

Fig. 5.
Fig. 5.

Mean proportions of ‘Honeycrisp’ fruit meeting Washington Extra Fancy standards for red color coverage thresholds for Honeycrisp apple in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied (N = 3). Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

Citation: HortScience 58, 11; 10.21273/HORTSCI17339-23

Table 4.

Mean proportions of ‘Honeycrisp’ fruit belonging to five red color coverage classes (0% to 20%, 20% to 40%, 40% to 60%, 60% to 80%, and 80% to 100%) with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied in 2022.

Table 4.

Evaporative cooling also appeared to improve red color. Over both years, treatments with evaporative cooling had 54% of fruit meet the color requirements for Washington Extra Fancy compared with only 49% in treatments without evaporative cooling (P = 0.0912). The mechanism for these increases in red color is likely due to lower fruit temperatures, which provides a better environment for red color development based on the findings of Marais et al. (2001) and Gouws and Steyn (2014).

Conclusion

Netting was a more effective sunburn mitigation strategy than evaporative cooling. The use of evaporative cooling did not significantly decrease the proportion of fruit with severe sunburn compared with the untreated trees but had a greater proportion of fruit with red color coverage in the range of 60% to 80%. Netting retraction 10 d before harvest did not increase the proportion of apples with a severe incidence of sunburn compared with the fruits from the trees with no net retraction and was significantly lower than those from trees without nets. Netting retraction near harvest increased the proportions of fruit with sufficient red color while limiting sunburn incidence and severity. Netting can be retracted near harvest to provide season-long sunburn, wind, and hail protection but allow light to induce better fruit color development in the last stage of fruit ripening.

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  • Reig G, Donahue DJ, Jentsch P. 2019. The efficacy of four sunburn mitigation strategies and their effects on yield, fruit quality, and economic performance of Honeycrisp CV. apples under Eastern New York (USA) climatic conditions. Int J Fruit Sci. 20:541561.

    • Search Google Scholar
    • Export Citation
  • Saure MC. 1990. External control of anthocyanin formation in apple. Scientia Hortic. 42:181218.

  • Schrader LE, Sun J, Felicetti D, Seo J-H, Jedlow L, Zhang J. 2004. Stress-induced disorders: Effects on apple fruit quality. Proceedings of the Washington Tree Fruit Postharvest Conference (online).

  • Schrader L, Sun J, Zhang J, Felicetti D, Tian J. 2008. Heat and light-induced Apple Skin Disorders: Causes and prevention. Acta Hortic. 772:5158.

    • Search Google Scholar
    • Export Citation
  • Serra S, Borghi S, Mupambi G, Camargo-Alvarez H, Layne D, Schmidt T, Kalcsits L, Musacchi S. 2020. Photoselective protective netting improves “Honeycrisp” fruit quality. Plants. 9:1708. https://doi.org/10.3390/plants9121708.

    • Search Google Scholar
    • Export Citation
  • Shahak Y. 2012. Photoselective netting: An overview of the concept, research and development and practical implementation in agriculture. Acta Hortic. 1015:155162. https://doi.org/10.17660/ActaHortic.2014.1015.17.

    • Search Google Scholar
    • Export Citation
  • Siegelman HW, Hendricks SB. 1958. Photocontrol of anthocyanin synthesis in apple skin. Plant Physiol. 33:185190.

  • Van den Dool K. 2006. Evaporative cooling of apple and pear orchards (MS Thesis). Stellenbosch University, Stellenbosch, South Africa.

  • Wagenmakers PS, Callesen O. 1995. Light distribution in Apple Orchard Systems in relation to production and fruit quality. J Hortic Sci. 70:935948.

    • Search Google Scholar
    • Export Citation
  • Waite JM, Kelly EA, Zhang H, Hargarten H, Waliullah S, Altman NS, dePamphilis CW, Honaas L, Kalcsits L. 2023. Transcriptomic approach to uncover dynamic events in the development of mid-season sunburn in apple fruit. G3: Genes, Genomes, Genetics, p.jkad120.

  • Wand SJE, Steyn WJ, Mdluli MJ, Marais SJS, Jacobs G. 2020. Overtree evaporative cooling for fruit quality enhancement. SA Vrugte J. 2(1):1821.

    • Search Google Scholar
    • Export Citation
  • Willsea N, Blanco V, Rajagopalan K, Campbell T, Howe O, Kalcsits L. 2023. Reviewing the tradeoffs between sunburn mitigation and red color development in apple under a changing climate. Horticulturae. 9(4):492.

    • Search Google Scholar
    • Export Citation
  • Fig. 1.

    Guide wires attached to the trellis system which support the nets as well as the evaporative cooling system running during a hot afternoon (left). The setup of one replication plot before retraction over individual rows of 12 trees (right).

  • Fig. 2.

    Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature and three different netting treatments (N = 3) (nets retracted 10 d before harvest, nets deployed until harvest, and no nets all year).

  • Fig. 3.

    Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature, treatments with evaporative cooling, and treatments without evaporative cooling (N = 3).

  • Fig. 4.

    Mean proportions of total fruit (N = 3) with sunburn exceeding SB2 based on the scale developed by Schrader et al. (2004), which would result in cullage in a commercial setting in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied. Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

  • Fig. 5.

    Mean proportions of ‘Honeycrisp’ fruit meeting Washington Extra Fancy standards for red color coverage thresholds for Honeycrisp apple in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied (N = 3). Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

  • Arakawa O. 1988. Photoregulation of anthocyanin synthesis in apple fruit under UV-B and red light. Plant Cell Physiol. 29(8):13851389. https://doi.org/10.1093/oxfordjournals.pcp.a077651.

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  • Gindaba J, Wand SJE. 2005. Comparative effects of evaporative cooling, kaolin particle film, and shade net on sunburn and fruit quality in apples. HortScience. 40:592596. https://doi.org/10.21273/HORTSCI.40.3.592.

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  • Gindaba J, Wand SJE. 2008. Comparison of climate ameliorating measures to control sunburn on ‘Fuji’ apples. Acta Hortic. 772:5964. https://doi.org/10.17660/ActaHortic.2008.772.6.

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  • Glenn DM, Prado E, Erez A, McFerson J, Puterka GJ. 2002. A reflective, processed-kaolin particle film affects fruit temperature, radiation reflection, and solar injury in apple. J Am Soc Hortic Sci. 127:188193. https://doi.org/10.21273/JASHS.127.2.188.

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  • Gouws A, Steyn WJ. 2014. The effect of temperature, region, and season on red colour development in apple peel under constant irradiance. Scientia Hortic. 173:7985. https://doi.org/10.1016/j.scienta.2014.04.040.

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  • Hengari S, Theron KI, Midgley SJE, Steyn WJ. 2014. Response of Apple (Malus domestica Borkh.) fruit peel photosystems to heat stress coupled with moderate photosynthetic active radiation at different fruit developmental stages. Scientia Hortic. 178:154162. https://doi.org/10.1016/j.scienta.2014.08.019.

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  • Iglesias I, Alegre SA. 2006. The effect of anti-hail nets on fruit protection, radiation, temperature, quality, and probability of Mondial Gala apples. J Appl Hortic. 8:91100.

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  • Iglesias I, Salvia J, Torguet L, Cabús C. 2002. Orchard cooling with overtree microsprinkler irrigation to improve fruit colour and quality of ‘Topred Delicious’ apples. Scientia Hortic. 93:3951.

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  • Kalcsits L, Musacchi S, Layne DR, Schmidt T, Mupambi G, Serra S, Mendoza M, Asteggiano L, Jarolmasjed S, Sankaran S, Khot LR. 2017. Above and below-ground environmental changes associated with the use of photoselective protective netting to reduce sunburn in apple. Agr For Meteorol. 237:917.

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  • Khemira H, Lombard PB, Sugar D, Azarenko AN. 1993. Hedgerow orientation affects canopy exposure, flowering, and fruiting of ‘Anjou’ pear trees. HortScience. 28:984987.

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  • Lugaresi A, Steffens CA, Souza MP, Amarante CV, Brighenti AF, Pasa M, Martin MSD. 2022. Late summer pruning improves the quality and increases the content of functional compounds in Fuji apples. Bragantia. 81:e3122. https://doi.org/10.1590/1678-4499.20210234.

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  • Marais E, Jacobs G, Holcroft DM. 2001. Colour response of ‘Cripps Pink’ apples to postharvest irradiation is influenced by maturity and temperature. Scientia Hortic. 90:3141.

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  • Morales-Quintana L, Waite JM, Kalcsits L, Torres CA, Ramos P. 2020. Sun injury on Apple Fruit: Physiological, biochemical and molecular advances, and future challenges. Scientia Hortic. 260:108866. https://doi.org/10.1016/j.scienta.2019.108866.

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  • Munné-Bosch S, Vincent C. 2019. Physiological mechanisms underlying fruit sunburn. Crit Rev Plant Sci. 38:140157.

  • Mupambi G, Anthony BM, Layne DR, Musacchi S, Serra S, Schmidt T, Kalcsits LA. 2018. The influence of protective netting on tree physiology and fruit quality of apple: A review. Scientia Hortic. 236:6072.

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  • Musacchi S, Serra S. 2018. Apple fruit quality: Overview on pre-harvest factors. Scientia Hortic. 234:409430.

  • Pruett M, Kalcsits L, Khot L, Peters T, Stockle C, Rajagopalan K. 2021. Climate change implications and management options for sunburn risk in apples. AGU Fall Meeting Abstracts; GC43C-08.

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  • Racskó J, Nagy J, Szabó Z, Major M, Nyéki J. 2005. The impact of location, row direction, plant density and rootstock on the sunburn damage of apple cultivars. Int J Hortic Sci. 11(1):1930. https://doi.org/10.31421/ijhs/11/1/554.

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  • Racskó J, Szabó Z, Miller DD, Soltész M, Nyéki J. 2009. Sunburn incidence of apples is affected by rootstocks and fruit position within the canopy but not by fruit position on the cluster. Int J Hortic Sci. 15(4):4551.

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  • Reig G, Donahue DJ, Jentsch P. 2019. The efficacy of four sunburn mitigation strategies and their effects on yield, fruit quality, and economic performance of Honeycrisp CV. apples under Eastern New York (USA) climatic conditions. Int J Fruit Sci. 20:541561.

    • Search Google Scholar
    • Export Citation
  • Saure MC. 1990. External control of anthocyanin formation in apple. Scientia Hortic. 42:181218.

  • Schrader LE, Sun J, Felicetti D, Seo J-H, Jedlow L, Zhang J. 2004. Stress-induced disorders: Effects on apple fruit quality. Proceedings of the Washington Tree Fruit Postharvest Conference (online).

  • Schrader L, Sun J, Zhang J, Felicetti D, Tian J. 2008. Heat and light-induced Apple Skin Disorders: Causes and prevention. Acta Hortic. 772:5158.

    • Search Google Scholar
    • Export Citation
  • Serra S, Borghi S, Mupambi G, Camargo-Alvarez H, Layne D, Schmidt T, Kalcsits L, Musacchi S. 2020. Photoselective protective netting improves “Honeycrisp” fruit quality. Plants. 9:1708. https://doi.org/10.3390/plants9121708.

    • Search Google Scholar
    • Export Citation
  • Shahak Y. 2012. Photoselective netting: An overview of the concept, research and development and practical implementation in agriculture. Acta Hortic. 1015:155162. https://doi.org/10.17660/ActaHortic.2014.1015.17.

    • Search Google Scholar
    • Export Citation
  • Siegelman HW, Hendricks SB. 1958. Photocontrol of anthocyanin synthesis in apple skin. Plant Physiol. 33:185190.

  • Van den Dool K. 2006. Evaporative cooling of apple and pear orchards (MS Thesis). Stellenbosch University, Stellenbosch, South Africa.

  • Wagenmakers PS, Callesen O. 1995. Light distribution in Apple Orchard Systems in relation to production and fruit quality. J Hortic Sci. 70:935948.

    • Search Google Scholar
    • Export Citation
  • Waite JM, Kelly EA, Zhang H, Hargarten H, Waliullah S, Altman NS, dePamphilis CW, Honaas L, Kalcsits L. 2023. Transcriptomic approach to uncover dynamic events in the development of mid-season sunburn in apple fruit. G3: Genes, Genomes, Genetics, p.jkad120.

  • Wand SJE, Steyn WJ, Mdluli MJ, Marais SJS, Jacobs G. 2020. Overtree evaporative cooling for fruit quality enhancement. SA Vrugte J. 2(1):1821.

    • Search Google Scholar
    • Export Citation
  • Willsea N, Blanco V, Rajagopalan K, Campbell T, Howe O, Kalcsits L. 2023. Reviewing the tradeoffs between sunburn mitigation and red color development in apple under a changing climate. Horticulturae. 9(4):492.

    • Search Google Scholar
    • Export Citation
Noah Willsea Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Victor Blanco Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Orlando Howe Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Thiago Campbell Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Erica Casagrande Biasuz Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Lee Kalcsits Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA; and Department of Horticulture, Washington State University, Pullman, WA 99164, USA

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Contributor Notes

L.K. is the corresponding author. E-mail: lee.kalcsits@wsu.edu.

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  • Fig. 1.

    Guide wires attached to the trellis system which support the nets as well as the evaporative cooling system running during a hot afternoon (left). The setup of one replication plot before retraction over individual rows of 12 trees (right).

  • Fig. 2.

    Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature and three different netting treatments (N = 3) (nets retracted 10 d before harvest, nets deployed until harvest, and no nets all year).

  • Fig. 3.

    Average maximum daily temperature for the retraction periods in 2021 and 2022 for air temperature, treatments with evaporative cooling, and treatments without evaporative cooling (N = 3).

  • Fig. 4.

    Mean proportions of total fruit (N = 3) with sunburn exceeding SB2 based on the scale developed by Schrader et al. (2004), which would result in cullage in a commercial setting in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied. Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

  • Fig. 5.

    Mean proportions of ‘Honeycrisp’ fruit meeting Washington Extra Fancy standards for red color coverage thresholds for Honeycrisp apple in 2021 and 2022 with no netting, netting deployed until harvest, or nets retracted 10 d before harvest and then either evaporative cooling (EC) or no EC applied (N = 3). Letters indicate significant differences among means determined using a Tukey’s honestly significant difference test (α = 0.05).

 

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