Begin spraying when buds begin to swell in the spring. Later in the season the pustules are dark colored. The disease may be severe enough to cause leaf drop. Although rust infections are not considered serious, they may result in heavy defoliation of young trees. White powdery growth on leaf surfaces may become heavy late in the season, especially on tender leaves of sprouts.
Spots are very thick, jet black, discrete and about one-fourth inch in diameter.
It looks like a drop of tar on the leaf. Rake up an burn dead leaves, as the fungus overwinters on them. Spray early in April with a fungicide. Most willow species are highly susceptible. Plants suddenly wilt and die, leaves usually hanging on the plant.