Necrotic leaf blotch, which is a physiological disorder and not a disease, has been manifesting throughout the area and is predominantly seen on the leaves of Golden Delicious, as well as those cultivars with Golden Delicious as a parent.
Necrotic leaf blotch, which is a physiological disorder and not a disease, has manifests itself in late summer and is predominantly seen on the leaves of Golden Delicious, as well as those cultivars with Golden Delicious as a parent (Pink Lady, GoldRush, Gala, Jonagold). This disorder is characterized by irregularly shaped brown blotches on the leaves, limited by the veins. Necrotic areas can range in size and midshoot leaves are most affected. Affected leaves turn yellow in about 4 days and subsequently fall off the tree. Other characteristics of the disorder are that the symptoms develop suddenly, appearing overnight and it can occur in waves from July through August. The disorder tends to be more common and severe later in the summer; however, usually appearing when a cool, rainy period is followed by hot summer weather. Some orchards or trees within an orchard may show little or no defoliation, while other orchards or trees reach 50% defoliation or more.
Although no bacteria or fungi have been associated with the necrotic leaf blotch, zinc oxide (ziram) applied in three to four midcover sprays, and two foliar applications of manganese have shown to be effective in reducing necrotic leaf blotch incidence.
When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one's own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from Crop Data Management Systems. Specific chemical recommendations are in: the Penn State Tree Fruit Production Guide and the Spray Bulletin for Commercial Fruit Growers for VA/WV/MD.