Nectrotic Leaf Blotch and Apple

This year necrotic leaf blotch has been noticed in many apple growing areas in Ontario. Necrotic leaf blotch is a relatively common disease that is considered to be restricted to Golden Delicious cultivars and its offspring. The disease is a physiological disorder that usually starts to appear in apple orchards in late June or early July, but was observed in orchards as early as May this year. Necrotic leaf blotch is usually most severe in the latter part of the growing season.

Generally, symptoms only appear on mature leaves on the base of the center of upright, succulent, rapid growing shoots. Infected leaves initially have necrotic yellow blotches on them, and eventually irregular brown blotches appear on the leaves (Fig. 6). Infected leaves often turn yellow and drop off a few days after the necrotic blotches first appear.

This disease does not appear to be caused by a fungus, bacterium, air pollutant or nutrient deficiency. It is considered to be a physiological disorder that occurs when a cool rainy period of 4 to 5 days precedes several hot, sunny days. It is considered to be linked to a hormonal imbalance in the tree.

Although leaf blotch is not associated with any fungus, extension agents in the U.S. recommend the use of EBDC fungicides during cover sprays to reduce symptoms of the disease. In most years control measures are not necessary. Trees that have an annual moderate crop of fruit have less necrotic leaf blotch than trees that have a biennial bearing habit or a light fruit crop. Golden Delicious trees pruned to a central leader also have less leaf blotch than those pruned to an open center.

Figure 6 - Necrotic leaf blotch symptoms