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James A. Chatfield, Ohio State University Extension, Northeast District/Horticulture and Crop Science; Nancy A. Taylor, Erik A. Draper, Stephen Nameth, Joseph F. Boggs, |
There are a number of different anthracnose diseases on trees in Ohio. It was an average year in general for incidence of these diseases. Some short profiles of common anthracnose diseases follow.
Sycamore Anthracnose
Sycamore anthracnose (Apiognomonia veneta) is a potentially serious disease of American sycamore and to a lesser extent London planetree. Susceptibility of London planetree varies considerably with seed source. The fungus overwinters on twig tissue on the tree with spores splashing to new buds, shoots, and leaves in the spring, with disease being enhanced by cool, wet conditions during shoot and leaf development. Considerable defoliation, sometimes with complete leaf loss, occurs on many trees by late spring in some years. Trees typically re-leaf by early to mid summer and are less susceptible to continued infections because of warmer, drier conditions.
Maple Anthracnose
Maple anthracnose (Kabatiella apocrypta) is generally not severe on maple but can cause considerable unsightliness from brownish leaf blotches and some leaf drop when moist weather conditions make the disease particularly severe. The most common symptoms include brownish discoloration along veins, varying from discrete spots to irregular patches of discoloration bordered by veins.
Dogwood Anthracnose
Dogwood anthracnose (Discula destructiva) has become prominent in certain areas in recent years, especially on flowering dogwood (Cornus florida). Dogwood anthracnose is most severe where cool, moist conditions occur during the summer, such as in higher elevation areas, and in densely vegetated shady sites with poor air movement. Leaf symptoms include irregular brown blotches bordered in purple on upper leaf surfaces. Stem symptoms include twig cankering and dieback, often with visible fungal fruiting bodies on dead twigs. Attached wilted, brown leaves often persist into the next spring instead of dropping in the fall.
Ash Anthracnose
Ash anthracnose (Gnomoniella fraxini) commonly causes at least some leaf drop on landscape ashes each year, with blotchy grayish to brownish blotch-like lesions occurring on ash leaflets.
Karen Jacobs and co-workers at Morton Arboretum in Chicago presented data this summer from their ash anthracnose study in a research poster session at the International Society of Arboriculture annual meeting in Milwaukee, Wisc. Two interesting points follow.
First, over a three-year period, they found that ash anthracnose incidence was considerably higher on green ash (Fraxinus pennsylvanica) than on white ash (Fraxinus americana), which is counter to what is commonly thought to be the case.
Second, in a look at eight different species of ash, the key factor in ash anthracnose incidence over the years appeared to be how early the particular species leafed out in the spring. Those that tend to leaf out earliest seem to exhibit the most ash anthracnose. The researchers note that this needs to be looked at over a longer period of time and that cultivar studies are needed. However, this data is interesting and consistent, considering that the key environmental factors for infection by the ash anthracnose fungus are cool and wet and on average the earlier, the cooler and the wetter.