Venturia pirina Aderh.
Occurrence and importance
Pear scab occurs in most pear-producing areas of the country. The disease is more prevalent in humid growing districts of the Northwest and in the northern part of the United States east of the Mississippi River, rather than in the irrigated or semi-arid regions of the West. Crop losses can be heavy in areas where climatic conditions favor disease development, unless orchard spray programs are carefully followed. Most commercial pear varieties are susceptible to the disease. Some important varieties that can be seriously affected are Anjou, Bartlett, Comice, Easter, Flemish Beauty, Forelle, Seckel, and Winter Nelis. The Bosc pear is susceptible only when young.
The disease attacks the leaves, fruits, and young twigs of pear in the orchard. When very young fruits are attacked, they drop from the tree or become either misshapen or badly scabbed. Later infections may be more numerous, but the spots are generally smaller. Large irregular scab spots, however, can result from merging lesions. Scab lesions enlarge as the fruit develops, becoming russeted or corky by harvest time (see photo). A fringe of dark fungal growth may persist at the edges of the lesion. Generally, scab spots on pears are larger and rougher than those on apples.
Late-season infections may be visible at picking time or may develop in cold storage. Such scab spots are quite small and dark and are referred to as "pinpoint" scab. As in apple scab, certain stages of orchard scab may enlarge slightly, but not significantly, in storage.
Venturia pirina, the cause of pear scab, is closely related to the apple scab organism and follows the same course of infection and development.
The disease must be controlled in the orchard. Spraying is necessary and should conform with the recommendations of the State agricultural experiment station or extension service.
Scab on pear