Scab can affect fruit, leaves and shoots. It first appears on fruits as small dark spots about six to eight weeks after petal fall. On mature fruits, the fungus forms small, circular, sooty-brown spots or freckles which become scabby. These can merge to form large, irregular dark brown lesions. When infection is severe, the fruit can crack, shrivel and fall prematurely. On apricot fruit the disease should not be confused with Shot-hole, which causes raised scabs on the fruit surface; by contrast Scab lesions are pale green and remain flush with the fruit surface. On peaches, lesions are flat, circular black spots up to 3 mm in diameter. When nectarines are affected, the skin loses its pigment and becomes pale green to cream in colour. The centre of each spot is dark with the development of spores.
Leaf infections appear as sooty or olive blotches on the underside of leaves, and as dark lesions running along the mid-rib and petiole. Severe leaf infection can cause defoliation, but in some cases, little or no leaf infection can be found even when the fruit is badly affected. On the shoots, small brown lesions with slightly raised margins may appear. The margins of these lesions become olivaceous where the pathogen is sporulating.
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