Diseases of glasshouse plants (1923) Diseases of glasshouse plants diseasesofglassh1923bewl Year: 1923 112 DISEASES OF GLASSHOUSE PLANTS produced on the upper surface of the leaves, varying in diameter from an eighth of an inch to patches covering haK the leaf. (Fig. 32). The tissue round the spots turns yellow, and, as the spots become old, minute dark pycnidia or fruiting bodies are distributed over the surface. Ulti- mately the leaves fall, and as the diseased plants lose their fohage they become weakened and stunted blooms are produced. On the diseased areas conidia are produced in great
Diseases of glasshouse plants (1923) Diseases of glasshouse plants diseasesofglassh1923bewl Year: 1923 112 DISEASES OF GLASSHOUSE PLANTS produced on the upper surface of the leaves, varying in diameter from an eighth of an inch to patches covering haK the leaf. (Fig. 32). The tissue round the spots turns yellow, and, as the spots become old, minute dark pycnidia or fruiting bodies are distributed over the surface. Ulti- mately the leaves fall, and as the diseased plants lose their fohage they become weakened and stunted blooms are produced. On the diseased areas conidia are produced in great abundance during the sum- mer and autumn months, and in consequence any new fohage is quickly in- fected. Infected leaves may remain green through the winter and so carry the infection over to the next season. Mrs. Alcock (1) has shown also that in this country the fungus may hibernate on the young wood of the previous season. On such parts she found discoloured areas, which on examination proved to contain abund- ant mycehum, and compact fungal masses bearing in- numerable spores of the leaf blotch parasite. This discovery is of considerable importance as affecting methods of control for this disease. Not only must all infected leaves be removed from the tree or collected from the ground at the base and burned, but attention must be paid to the fungal patches occurring on the new wood. These should be removed by pruning, but the operation must be conducted judiciously, in accordance with the requirements of the variety. So far as is known, the old pustules on two-year-old wood Fig. 32. Rose leaf blotch : (a) Diseased leaf, (6) spore cluster, (c) spores.
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