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Black Pox

Helminthosporium papulosum

Black pox, caused by Helminthosporium papulosum, causes fruit spot, leaf spot, and limb and twig canker. Golden Delicious is the most severely affected cultivar grown in the Southeast.

Symptoms

Fruit spots are small (from 1/16 to 1/4 inch in diameter), circular, sunken, and black. Leaf spots are light green with red halos and enlarge to about 1/2 inch in diameter. The center dies and becomes tan. Lesions on stems appear as conical, shiny black swellings.

Fruit spots Fruit spots Stem lesions
Fruit spots Fruit spots Stem lesions

 

Disease Cycle

The fungus overwinters in twig and bark cankers. Infections are initiated by conidia produced in these cankers and can occur on fruit as early as May and continue through the summer until harvest.

Control

Control is based on the use of a preventive fungicidal spray program, applied on a 2-week schedule, beginning in mid-May. Pruning to remove water sprouts with cankers will reduce the inoculum and aid in control.

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Format updated March 29, 2011