Diseases of glasshouse plants (1923) Diseases of glasshouse plants diseasesofglassh1923bewl Year: 1923 110 DISEASES OF GLASSHOUSE PLANTS Downy Mildew of the Rose.—This disease, while common on glasshouse roses, is somewhat difficult to detect. Frequently young plants appear to lack vigour for no obvious reason, but a careful examination of the leaves reveals the presence of minute fungal filaments. The causal organism, Peronospora sparsa Berk., is capable Fig. 31. Powdery mildew of the rose : («) Diseased leaves, (6) summer spores, (c) a perithecium, (d) ascus containing eight ascosporcs.
Diseases of glasshouse plants (1923) Diseases of glasshouse plants diseasesofglassh1923bewl Year: 1923 110 DISEASES OF GLASSHOUSE PLANTS Downy Mildew of the Rose.—This disease, while common on glasshouse roses, is somewhat difficult to detect. Frequently young plants appear to lack vigour for no obvious reason, but a careful examination of the leaves reveals the presence of minute fungal filaments. The causal organism, Peronospora sparsa Berk., is capable Fig. 31. Powdery mildew of the rose : («) Diseased leaves, (6) summer spores, (c) a perithecium, (d) ascus containing eight ascosporcs. of attackmg all leaves and young shoots. The first symptom of the disease is the sudden flagging of young, vigorous leaves, which readily fall off the stem if it is shaken gently. The shoot itseK droops and dies. Diseased leaves and shoots possess reddish-purple patches bearing a fungus growth. Gradually the disease develops until all the green tissues are destroyed.
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