Yellow-leaf, caused by the fungus Coccomyces hiemalis Higgins, is the most prevalent and destructive cherry disease in Iowa, since it often causes premature defoliation of both nursery and orchard trees. Early defoliation in nursery stock results in decreased growth during the current and subsequent years, and precludes all possibility of forcing the trees into marketable size in one growing season. In the orchard, defoliation may decrease fruit bud formation and vegetative growth and increase the amount of winterkilling.

All defoliated nursery stock must be held in the nursery row a second season, and even then many of the trees must be marketed at lower grades because of inferior size. Winterkilling in severely defoliated blocks is so common that yellow-leaf becomes the limiting factor in cherry culture.