General Types of Diseases
Fungal Leaf Spots
plant genera, species, or varieties. Leaf spot damage ranges from minor to severe depending on the interplay of fungus, host plant, and environmental conditions.
Symptoms
Ascochyta blight on clematis.
In t r o d u c t i o n
Depending on the fungus-host combination, leaf spots can vary in size, shape, and color. Some leaf spot fungi produce tiny, dark-colored fruiting bodies (spore-producing structures) in the spots and others develop distinctive-looking masses of spores. A hand lens can help you to spot these clues. Still other leaf spot fungi produce no conspicuous signs. When conditions are favorable, leaf spots may expand in size or number, merging to create larger dead areas referred to as leaf blight. In severe cases, all of the foliage may become blighted.
Ecology
Fungal leaf spots are among the most commonly occurring diseases of herbaceous perennials. A multitude of fungi can cause leaf spot symptoms, including species of Alternaria, Ascochyta, Cercospora, Corynespora, Cylindrocladium, Cylindrosporium, Didymella, Entyloma, Fabraea, Marssonina, Phyllosticta, Pleospora, Ramularia, Septoria, and many others. Although some leaf spot fungi attack a wide range of perennials, many are specific to one or a few
Almost all leaf spot diseases thrive in warm, moist weather. To invade, spores of these fungi need leaf surfaces to remain wet for at least a minimum period of time — several to many hours — depending on the air temperature and the host plant. Prolonged spells of warm, rainy weather set the stage for severe leaf spot outbreaks. Most leaf spot fungi are adept at surviving unfavorable periods (winter or drought periods) burrowed inside dead
Heterosporium leaf spot on iris.
Stemphylium leaf spot on gladiolus.