LEAF SPOT DISEASES OF COMMERCIAL ORNAMENTAL PLANTS — THEIR RECOGNITION AND CONTROL
The taxonomy of fungi is a difficult topic. In the fungi there are some 47,000 known species. Imperfect fungi, with no known sexual stage, account for 15,000 species and many of these are capable of producing leaf spots.
While we might agree that disorders such as Black Spot of roses (Diplocarpon rosae), Leaf Blotch of chestnut (Guignardia aesculi), and Leaf Spot of willow (Marssonina spp.) should be easily recognised by horticulturists, I feel that this generalisation is incorrect and misleading. Advisory experience has taught me that the services of a mycologist is required to obtain a correct identification of leaf spot disorders.
Leaf spot of willow, for example, may be caused not only by Marssonina spp. but also by Ascochyta, Cercospora, Cylindrosporium, Phyllosticta, Ramularia, Septoria, and other fungi. There are more than 100 species of Cercospora. Regular control measures should not be considered until identification of the disorder is certain.
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