Phyllosticta solitaria Ell. & Ev.
Occurrence and importance
Blotch is widely distributed in the central and southern apple-growing districts of the country. The incidence of this midsummer disease of apples has been greatly reduced by the elimination of susceptible varieties and the use of modern fungicides. The varieties commonly affected are Rome Beauty, Northwestern Greening, Rhode Island Greening, Yellow Newtown, Yellow Transparent, and Dutchess. The disease is seen on the market occasionally.
The disease attacks leaves, twigs, and the fruits of apple. Fruits are infected early in the growing season and by midsummer exhibit dark, blotch-like lesions with fringed margins (top photo). The diameter of the blotch spots varies from 1/4 to 1/2 inch or more. Pycnidia, small, black fruiting structures, containing fungal spores, develop in the central portion of the hard, markedly sunken, and nearly black lesions. The fringed margins usually disappear as the spots merge to produce larger lesions.
Blotch lesions involve only the outer cell layers, and there is no rotting of the fruit tissues. However, badly blotched fruits are unmarketable, and any blotched fruits that arrive on the market are heavily discounted or rejected. Occasionally, blotch spots provide sites for secondary infections, of which blue mold rot and black rot are most common.
The causal fungus of the disease, Phyllosticta solitaria, attacks apple foliage and fruits in the orchard. Blotch infections can occur throughout much of the growing season in periods of warm, wet weather. Ordinarily, however, most infections occur relatively early in the growing season, when spring rains are frequent and the fruits are most susceptible to infection.
The disease is controlled by orchard sprays. The recommendations of the State agricultural experiment station or extension service regarding spray schedules should be followed.
Blotch on apple