Commonly, the term is used to mean black spot of roses (rose), a serious worldwide disease, except in arid regions, caused by the fungus Diplocarpon rosae. On rose plants, the spots are roundish and more than 1 cm (up to 0.5 inch) in diameter with fringed margins. Leaves on susceptible varieties turn yellow and drop early. Affected plants may defoliate twice in a season, are greatly weakened, produce fewer and inferior blooms, and are subject to canker diseases and winterkill. Large numbers of spores are formed in speck-size fruiting structures (acervuli) and disseminated by splashing rain, dew, overhead sprinkling, and gardeners working among wet plants. The spores germinate and penetrate rose tissue in 9 to 18 hours or longer; new leaf spots appear in 3 to 16 days and spores in 10 to 18 days. The cycle may be repeated throughout the growing season. Black spot may be controlled through adequate spraying or dusting.