Diseases of fruits and nuts Diseases of fruits and nuts diseasesoffruits120smit Year: 1941 106 California Agricultural Extension Service [Cir. 120 tlie disease have usually beeu weakened by g'ophers, crown gall, or somo other injurious influence. Phytophthora Canker, Pythiacystis Canker. On the trunks of heeled-in nursery trees, oval-shaped, dark-colored, dead spots sometimes appear on the smooth green bark (fig. 53). These spots, in wet weather and if the trees are covered with soil, may extend to several inches in length and may girdle and ruin the stock. If such trees are planted, llic ca
Diseases of fruits and nuts Diseases of fruits and nuts diseasesoffruits120smit Year: 1941 106 California Agricultural Extension Service [Cir. 120 tlie disease have usually beeu weakened by g'ophers, crown gall, or somo other injurious influence. Phytophthora Canker, Pythiacystis Canker. On the trunks of heeled-in nursery trees, oval-shaped, dark-colored, dead spots sometimes appear on the smooth green bark (fig. 53). These spots, in wet weather and if the trees are covered with soil, may extend to several inches in length and may girdle and ruin the stock. If such trees are planted, llic cankers stop growing, the fungus, a species of PliytophtJiora, dies out Fig. 55.—Pear stigmonose exterior view. in them and, if not too badly injured, the tree sends out growth below the lowest point where it is girdled or from the uninjured sides. Trees affected with this trouble will be more or less crippled in the manner suggested in the preceding sentence but may eventually recover, so that the grower may use his own judgment whether or not to plant them. In nurseries where this disease is serious (almond and peach trees are also sometimes affected), care should be taken when heeling in stock to cover only the roots with soil. In districts of heavy winter rainfall, some nurseries carry the stock in covered buildings or basements and cover the roots with shavings or 'shingle tow' instead of soil. Powdery Mildew.—Young fruit sometimes becomes covered with typ- ical, white, powdery mildew. This dries down and leaves a hard, brown, scabby area on the pear. The fungus, a species of Podosphaera, has been observed particularly on the Comice variety in foggy places or seasons; it is not general.
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