Fall infection is more frequent. Newly developing tissues are very susceptible to the fungus. Infection may occur late in the season, if growth is prolonged and encouraged by heavy pruning, high fertility and excessive moisture. An infection may begin within seven hours on a wet surface when temperatures are 20-24 o C. Prolonged wet periods promote and enhance the severity of the disease. Following infections, high temperatures intensify the severity of symptoms.
Mature leaves appear to be more resistant.
The disease begins as small lesions first appearing as tiny yellowish spots. As the fungus advances in to the water conducting tissues, diseased shoots fade becoming light green and eventually turning reddish brown. A greyish band or canker can be noted at the base of infected shoots. Diseased shoots remain on the plant for sometime eventually turning grey. This discoloration occurs later during the growing season.