Fruit Disorders: Prevention of Scarf Skin on Apple Fruit

Scarf skin is a physiological disorder of apple fruit that causes a dull gray cloudy or waxy appearance on the surface of the peel (epidermis) where it is most readily observed on varieties with a red or dark red background.
Fruit Disorders: Prevention of Scarf Skin on Apple Fruit - Articles

Updated: November 12, 2018

Fruit Disorders: Prevention of Scarf Skin on Apple Fruit

Photo: Tara Baugher, Penn State

Scarf skin can result in loads of ‘Gala’ being rejected by retailer, who fear that consumers may mistake these symptoms for pesticide residue. Widely planted red strains, such as ‘Buckeye’ and 'Ultima,' are particularly susceptible. Penn State Extension collaborated with three growers in 2018 to evaluate two formulations of GA4+7 for managing scarf skin on Gala apples. Both formulations significantly reduced the incidence and severity of the disorder.


Figure 1. Scarf skin on ‘Buckeye Gala.’ Photo: H. Edwin Winzeler, Penn State

Scarf skin occurs during the early development of the fruit. Several sprays of a plant growth regulator, GA4+7, at 10-day intervals starting at petal fall (PF), have shown potential for reducing the severity of scarf skin. The objective of this study was to evaluate two formulations of GA4+7 for managing scarf skin incidence and severity, along with other possible effects on fruit size and quality.

Procedures

We compared Novagib® 5L (5% GA4+7) and/or ProVide® 10SG (10% w/w GA4+7) with an untreated control. The trees otherwise received fertilizers, and crop protectant sprays according to local recommendations.

Four sprays of each gibberellin product were applied at two orchards, starting at PF and at ten-day intervals after that. Sprays began at first cover in the third orchard. Each product was applied to one acre of orchard. Sprays were applied in 100 gallons per acre (preferred), or in 50 gallons per acre, and not tank mixed with crop protectant chemicals, surfactants or other spray additives.
Uniform plots of approximately one-quarter of an acre in size were selected in orchards of red strains of ‘Gala’ with a history of scarf skin. Each plot received GA4+7 treatments at the maximum rate per acre, as shown in Table 1.

Table 1. Scarf skin treatments

Treatment NumberNovagib® 5L Fluid oz per acreProVide® 10SG Dry oz (g) per acre
100
24 × 40
303.5 (100) × 4

Fruit set per cm2 limb cross-sectional area was evaluated on two uniform, well-exposed limbs of two randomly selected trees per plot. One hundred fruits per plot were non-selectively sampled at harvest. Fruit weight and length: diameter ratio were measured, and means calculated. Scarf skin coverage was evaluated by three to five individuals, using a visual rating scale of 1= none to a trace to 5= severe scarf skin evident on the shoulder and cheek of the apple (Figure 2).


Figure 2. Scarf skin severity rating classes used in the study. Rating scale: 1 = no scarf to a trace of very mild scarf; 2 = trace of scarf to mild scarf, does not detract from commercial value; 3 = moderate (≤15%) scarf, does not detract from commercial value; 4 = prominent scarf, patches of scarf surrounding lenticels leading to a dull grayish appearance, detracts from visual clarity of apple color, distracts from appreciation of apple appearance, is of concern in commercial setting; and, 5 = dominant scarf; a primary visual impression concerns the presence of scarf, detracts from commercial value, is commercially unacceptable in some markets for some varieties. Photo: H. Edwin Winzeler, Penn State

Results and Discussion

Both GA4+7 formulations reduced the incidence and severity of scarf skin (Table 2). These results were consistent at all three commercial orchards and were also documented in research plots at the Penn State Fruit Research and Extension Center (data not shown). Although it is recommended that a spray program for scarf skin start as soon after petal fall as is practical, the results from Orchard 2, where sprays started later, gave similar results this year. We also observed a slight increase in fruit elongation, but these differences were minimal – on the order of 2-5%. Growers who want to increase the length of Gala apples should use the proprietary mixtures of GA+6BA (Promalin®, Perlan®) during bloom, as labeled.

Table 2. Effect of GA4+7 sprays on scarf skin and fruit dimensions of Gala apples, Pennsylvania, 2018.

Orchard 1

TreatmentScarf skin ratingFraction out of grade (% >3 score)Length (cm)Diam (cm)L:D RatioWeight (g)
Control3.60 a58 a6.26.90.90 b298
Novagib®3.08 b37 b6.36.90.92 a299
p-value0.0020.005N.S.N.S.0.001N.S.

Orchard 2

TreatmentScarf skin ratingFraction out of grade (% >3 score)Length (cm)Diam (cm)L:D RatioWeight (g)
Control4.40 a42.1 a6.887.180.958 b355
Novagib®3.67 b29.3 c7.157.190.994 a363
Provide®4.03 ab35.6 b7.037.150.983 a365
p-value0.010N.S.N.S.0N.S.

Orchard 3

TreatmentScarf skin ratingFraction out of grade (% >3 score)Length (cm)Diam (cm)L:D RatioWeight (g)
Control3.68 a29.8 a6.54 b6.351.03264
Novagib®3.04 b15.6 b6.76 ab6.471.04280
Provide®3.05 b16.2 b6.87 a6.511.06281
p-value0.020.010.04N.S.N.S.N.S.

Scarf skin has been referred to as “smooth russet,” and it is caused when the cuticle and epidermis layers become separated from the highly pigmented layers of cells below. The two disorders are physiologically related and have essentially the same anatomical origin. One can think of it as russet that does not break the surface of the skin. For this reason, GA4+7 is effective for reducing both defects.

Acknowledgments

Thanks to our grower-cooperators, Mt. Ridge Farms, Lerew Orchard, and Keim Orchard, for providing orchard plots and donating fruit samples, as well as for making the spray applications. Thanks also to Fine Americas (Novagib®), Valent BioSciences (ProVide®), and Rice Fruit Company for providing products for testing.

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