Southeastern Apple Production

PLANT PATHOLOGY

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.


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.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

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Department of Plant Pathology
North Carolina State University
Raleigh, NC 27695 USA

Web Crafters: Anne S. Napier and Steve Schoof
Email: steve_schoof@ncsu.edu

Format updated March 29, 2011