WSU Tree Fruit Research & Extension Center

Tree Fruit Market Diseases

Thursday, November 23, 2017

WSU-TFREC/Postharvest Information Network/Tree Fruit Market Diseases/heat



Serious heat injury to most varieties of apples is rare while on the tree. In 1918 and again in 1924, unusually high air temperatures of 106° to 107 °F for several days following a cool period caused serious heat injury to several varieties of apples both in the East and Northwest.

Injury ranged from a single area of collapsed tissues to the involvement of the entire fruit. In general most varieties were so injured that they had lumpy or irregular surfaces due to the killed and collapsed tissues immediately below the surface. Two striking, but different, symptoms were observed on Northwestern Greening. In some fruits the affected surface appeared water soaked and retained its green color while beneath the skin the tissues were wet, firm, and brown. The most seriously affected fruits of Northwestern Greening looked as if they were baked.

The York Imperial variety, grown extensively in the Cumberland-Shenandoah district, is quite subject to heat injury. The injury occurs at air temperatures below 100 °F and is seen every few years. Two types of symptoms have been observed.

The symptom most frequently seen is a crescent-shaped area (top photo) or a complete circle of sunken tissues on the blush side of the fruit, in which the central area appears normal. When cut, the tissues beneath the collapsed surface margin are brown and spongy (middle photo) and may have hollow pockets. This type of injury probably occurs late in August or early in September, because there is no distortion in the fruits due to additional growth.

In the second type of heat injury on York Imperial, the fruit surface is not collapsed. In the affected area, the skin may be normal in color or may be brown. When cut crosswise, the affected tissues are wet, dark brown (bottom photo), firm, and extremely bitter flavored. This type of injury develops after there is considerable sugar in the fruits. The injury has been observed at harvest following several days of air temperatures of 88° to 90 °F during the last week of September.

Excepting for the firm, water-soaked area just described and for the baked appearance of the Northwestern Greening described earlier, all other types of heat injury show one or more collapsed surface areas with dry, spongy tissues immediately beneath. These symptoms are distinct from boron-deficiency cork, York spot, or other apple disorders or injuries.

Heat injury while on the tree
Heat injury while on the tree

Heat injury while on the tree
Heat injury while on the tree

Heat injury, late season, York Imperial, while on the tree
Heat injury, late season, York Imperial, while on the tree

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