Plum scab, the same as found on the peach, was observed several years ago on the plum in Iowa. Subsequent observations were made in Delaware, Michigan, Indiana and elsewhere in the United States. It is common in Ontario on wild plums. In Michigan the De Soto variety is said to be particularly sensitive to scab. In Iowa cultivated varieties of Primus americana are reported as susceptible.
As in the case of peach scab, the chief losses result: (1) on account of marring the appearance of plums; they are unattractive and not of first-grade quality; (2) on account of the cracking which accompanies scab, allowing the Brown Rot fungus (Sclerotinia cinerea) to enter. The disease is far less common on the plum than on the peach, and in most plum - growing regions it may not be expected to assume dangerous proportions (see page 294 for fuller account).
Craig, J. A destructive disease affecting native plums. Canada Exp.
Farms Repts. 1892: 101. 1893. Pammel, L. H. New fungous diseases of Iowa. Plum scab or black spot. Journ. Myc. 7: 99 - 101. 1892. Jarvis, T. D. Fungus diseases affecting fruit trees. Plum scab.
Ontario Agr. Dept. Bul. 158: 27. 1907.