Citrus scab

Disease cycle. Conidia are produced on the surface of scab pustules. These spores spread to new susceptible tissue. There are two kinds of spores, clear oval shaped and colored spindle shaped (found in Florida and Brazil). The clear oval shaped type are spread by splashing rain and perish as soon as they dry, while the spindle-shaped form remain viable for a short time and are dispersed by wind for short distances.
Symptoms. Leaf and fruit - early scab pustules are a mixture of fungal and host tissue. These pustules are slightly raised and pink to light brown in color. Young foliar lesions superficially resemble young citrus canker and may have a slight water soaked margin. As fruit and leaf pustules develop, the small elevated pink spots become more defined and may form conical depressions nearby. As the pustules mature, they become warty and crack. Pustule color may progress to yellowish brown and eventually to a dirty grey. On lemons, tangerines, and sour orange, the growths are relatively raised. In contrast, on grapefruit the growths are flatter.