Drops of a clear, amber liquid can be found on the surface of Phytophthora spots. Expansion of leaf spots in moist weather is extremely rapid in susceptible cultivars and large sections of the leaf are rotted in a few days. White, powdery masses of spores are produced on these blights. When the weather becomes dry, lesions become tan to brown and have a dark brown to black edge. Exudates on the leaf surface associated with diseased tissue become yellow to brown and forms small crusts.
Some lesions are circular and resemble target spots.
The zones in the spot represent the growth rate differences of the fungus during warm moist hours and cooler or drier periods. In tolerant or resistant cultivars, diseased tissue falls away from spots forming holes in the leaf. When the petiole or leaf stalk becomes infected, rots are usually long, brown, and occur anywhere on the stalk. As the rot expands, the stalk becomes soft, and is unable to support the weight of the leaf and breaks. Corm rots are common in very susceptible cultivars such as Niue.