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Necrotic Leaf Blotch

Necrotic leaf blotch is a physiological disorder that affects only Golden Delicious and its bud sports (e.g., Smoothee).

Symptoms

The disorder is characterized by irregular necrotic blotches on mature leaves (Fig 1) many of which often turn yellow and abscise (Fig 2). Midshoot leaves are most severely affected. Affected areas on the leaves initially turn a pale green (Fig 3) and within several hours turn brown; older lesions appear tan to gray. Blotches are 1/4 to 1 inch in size and are often bordered by veins. The number of blotches on affected leaves varies from one to several. Not all affected leaves abscise, but some turn yellow and abscise within 1 week of the appearance of symptoms.

blotches on leaves yellowed leaves leaf with blotches
Fig 1. Blotches on leaves Fig 2. Yellowed leaves Fig 3. Blotches on leaf

Disease Cycle

The exact cause of necrotic leaf blotch is not known although it is associated with a rapid accumulation of gibberellins, which is triggered by periods of cool temperatures, low light intensity, and high soil moisture. The disorder occurs in distinct periods or waves during the summer and can result in up to 70% defoliation by harvest.

Control

Including dithiocarbamate fungicides or zinc oxide in the cover sprays beginning 4 to 6 weeks after petal fall can reduce the incidence and severity of necrotic leaf blotch.

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Format updated March 29, 2011