The disease is caused by a fungus, Phytophthora cactorum , which produces spores that are spread by wind, rain, splashing water, and surface water runoff.
Root rot is the most serious form of the disease.
Therefore, if foliar symptoms are present, preventing spread of the disease from foliage to roots is essential. Phytophthora leaf blight symptoms begin as dark, water-soaked lesions on the leaf surface. The lesions eventually become papery thin, brown, and dry. During wet, rainy periods, the disease will develop and spread rapidly, resulting in severe blighting of the foliage. The crown, or neck, of the plant may also be affected.