This page shows types of symptoms which appear on leaves. A typical example of each is presented. The white patches are the growth of causal fungus and give the disease its common name, as here on a leaf of Populus . Vernyl D. Pederson A closer view of a leaf with Apple Scab shows the dark sooty surface of the infections. Photo courtesy of H. A. Lamey LEAF RUST .
Some leaf infecting fungi cause very conspicuous symptoms.
LEAF SPOT . Many parasitic fungi cause discrete infections of limited size. This is a disorder caused by water stress. Compare the distinct pattern on this leaf to the leaves in the other pictures. Some leaf infecting fungi are not limited to discrete spots but can spread extensively in the leaf, causing necrotic blotches.