Category: Tree fruit

Superficial Scald in Apples: Strategies and Solutions

Emily Zobel on

By Agustina Salas (Candidate for B.S. in Biology Pontificia Universidad Católica de Chile) & Macarena Farcuh, Ph.D., UMD

What is superficial scald in apple fruits and what causes it?

Physiological disorders correspond to abnormalities that can occur in any of the apple tissues, and can result in loss of quality, marketability, and profitability, leading to increased loss and wastage of apples. These disorders are caused by abiotic factors such as genotype/genetic background, maturity at harvest, orchard/preharvest factors, seasonal variations, and postharvest storage conditions. It is important to mention that pathogens or mechanical damage do not lead to physiological disorders.

In particular, the physiological disorder of superficial scald in apples is the result of a chilling injury. Chilling injuries occur during cold storage at temperatures below the optimum range. During apple cold storage fruits can accumulate a-farnesene, a volatile compound present in the fruits’ wax layer. This compound can cause superficial scald when it oxidizes with atmospheric oxygen. Therefore, superficial scald generally develops during cold storage (more than 3 months in storage) but it is increased 3-7 days after taking the fruit out of cold storage.

Granny Smith apples with superficial scald on their skin.
Fig 1. Apples (Granny Smith) affected with superficial scald on their skin. Photo: Fresh Quarterly issue 9 June 2020.

Superficial scald is only restricted to the skin of the apples and usually on the shaded side. The symptoms appear as brown patches on the skin of the apple, which are diffuse (no defined edges between affected and unaffected skin) irregular, and light brown to dark brown to black in color. Superficial scald can also be accompanied by the development of a rough texture of the fruit.

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Apple Scab Alert!

Emily Zobel on
Despite cooler temperatures during the past few days, apple scab (Venturia inaequalis)  spores continue to mature. A significant apple scab infection event is forecasted April 5 to 7, 2022, in Pennsylvania and surrounding area. For those with green tissue present on their apple trees, protection is necessary for this event.
The apple scab fungus overwinters in infected leaves.  As it warms up in the spring they mature and produce spores that are discharged into air currents and carried to developing apple buds. The disease negatively affects fruit size and quality (due to blemishes and poor ripening). Over time, repeated defoliation from the disease reduces tree vigor, growth, and yield. 
Apple scrub leaf lesions.
Photo by Penn State Department of Plant Pathology & Environmental Microbiology Archives , Penn State University, Bugwood.org
Apple scab produces gray-to-olive green lesions on the leaves ( as seen above), but may also be seen on blossoms, sepals, petioles, pedicels, and fruit. On leaves, lesions first appear on the undersides of young leaves in the spring as they unfold and are exposed to infection. Leaves are susceptible to infection for about 5 days after they unfold. Fruit may become infected at any time in its development. Typical fruit lesions are distinct, almost circular, rough-surfaced, olive-green spots up to ¾ inch in diameter. 
Control information can be found on Penn State Extension website:  https://extension.psu.edu/2022-disease-update-apple-scab-infection-event-april-5-7-2022