Plant tissues infected the previous year produce spores that are rain splashed to new growth in the spring. These spots tend to form along the veins or be confined by them. Usually, a distinct margin develops between the dead and healthy leaf tissue. Heavily infected leaves may appear misshapen and curled.
Mature leaves tend to be more resistant to infection than immature leaves.
Older leaves develop small, brown spots in the summer during wet weather. Heaviest infections tend to be located in the lower portion of the trees where relative humidity is highest and leaves remain wet. Severe infections may result in defoliation and dieback of infected branches. When severe leaf loss occurs in the spring, trees usually try to produce a new flush of leaves to help compensate for leaf loss. Twigs infected during the growing season may often die before their buds are able to open the following spring, causing branch dieback.