This peculiar and interesting disease has been observed in New York State during the past five or six years. There are no extensive data as to its preference for varieties, although it has been observed especially on the Kieffer and Clairgeau. In some cases under attention the orchards showing red leaf, or crimson foliage, were located on a hillside, and the disease was confined to those individuals occupying the lower part of the orchard. Such trees also exhibit signs of general unthrifti-ness. Affected trees stand out prominently among their healthy neighbors and exhibit an entire foliage discoloration; a dark or purplish red color. The suggestion has been made that lack of vigor, of which red leaf is a sign, may be due to one or more factors. Such factors worthy of note are poor under - drainage, insufficient plant food, a diseased condition of the trunk or roots, and winter and drought injuries.
Stewart, F. C. Notes on New York plant diseases, I. Pear. Crimson foliage. New York (Geneva) Agr. Exp. Sta. Bul. 328: 371 - 372. 1910.