Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 DISEASES OF SPECIAL CROPS 81 Buckingham, Mammoth Black Twig, White Winter Pear- main, Winesap, and Ben Davis are resistant, the last al- most entirely so. In general the crab varieties are more suscep- tible than others. Black rot, canker (Sphcerop- sis Malorum Peck). — In many respects this disease closely re- sembles the bitter rot, particu- larly in that it appears both as rot of the fruit and as cankers upon the limbs, each of which is almost indistinguishable from bitter rot upon the similar
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 DISEASES OF SPECIAL CROPS 81 Buckingham, Mammoth Black Twig, White Winter Pear- main, Winesap, and Ben Davis are resistant, the last al- most entirely so. In general the crab varieties are more suscep- tible than others. Black rot, canker (Sphcerop- sis Malorum Peck). — In many respects this disease closely re- sembles the bitter rot, particu- larly in that it appears both as rot of the fruit and as cankers upon the limbs, each of which is almost indistinguishable from bitter rot upon the similar part. In some instances it also appears as a twig blight and as a leaf spot. Upon the fruit the spot, though sometimes of a darker hue, is often quite indistinguishable from that of the bitter rot. As seen under the hand lens the coils of exuding spores are black, instead of pink, as is the case with bitter rot. A compound microscope is necessary to bring out other distinguishing characters. The limb cankers, first studied by Paddock,1 consist of swellings with the bark rough, and black, or in many cases expose the black and decayed wood from which the bark has disappeared. This cankerous infection sometimes 1 Paddock, W., (Geneva) Agr. Exp. Sta. Bui. 163, December, 1899. G Fig. 29.—Apple black rot canker (sphaeropsose) showing numer- ous pycnidia. After Whetzel.
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