Common Wisconsin Tree Diseases and How to Identify Them (Part 2)
Wisconsin offers a variety of tree species that beautify our area in unique ways. Homeowners all over the area enjoy their trees and want to ensure their continued health. For this reason, American Landscape offers tree care and arboreal services, as well as diagnosis and treatment of all types of tree disease in the Milwaukee and Menomonee Falls area. In this post, we’ll continue our coverage of common Wisconsin tree diseases, so you can be informed about the conditions that can affect your trees.
Leaf blister
A number of species of the genus Taphrina are responsible for this disease. Leaf blister is named because it typically causes discrete, roundish bulges in leaf tissue, often with some cupping and twisting of the leaves. Defoliation rarely follows infection, but affected tissue sometimes has a fuzzy growth over the surface. Red oaks are especially susceptible, although other hosts are sometimes also affected. Like most other fungal leaf spots, each fungal species is host-specific.
Leaf blotch
This is the most prominent disease of horse chestnut, and most related members of Aesculus (buckeye) are susceptible. Leaf blotch commonly produces symptoms similar to anthracnose, beginning in midsummer. In nurseries, symptoms may show earlier. Aesculus species also are susceptible to a physiogenic “leaf scorch” condition that is associated more with a marginal burn of the foliage. However, the two can occur on the same plant. On flowering crab, leaf blotch typically shows more yellowing and blotchiness of foliage than on horse chestnut. As the disease progresses, affected leaves fall off.
Monilinia blight
Irregular blotches suddenly appear on foliage in May or June, especially on hawthorns. Entire twigs are sometimes affected. The damaged tissue frequently has a fuzzy fungal growth over the surface. At first, the tissue appears water-soaked and gray, but soon turns tan in color. Cool, moist conditions favor the disease, which does not spread after initial infections. You can protect trees by using appropriate fungicides where needed. Applications should be made at the same time as for cedar-hawthorn rust control.
Powdery mildew
This disease is found on many trees, especially in late summer. Symptoms include a white or gray surface of fungal spores and vegetative growth over leaves and twigs. Powdery mildew rarely requires control on trees, but several chemicals are registered and effectively control this disease if applied at the proper time.
Rust
Rust diseases usually are diagnosed by the masses of red or orange spores that develop over the leaves’ surfaces. On some shade trees, such as birch and cottonwood, leaves may become severely infected and drop off. On others, such as oak, the infection is barely perceptible. With still others, such as ash, there may be twisting, swelling, and malformation of affected tissue.
Virtually all rust diseases require a second, or alternate, host on which to complete the life cycle, including the juniper for hawthorn and flowering crab rust; certain pines for oak rust; Spartina (a Poaceous grass) for ash rust; and Larix laricina (eastern larch, or tamarack) for birch rust. In some cases, you can control rust by removing the less desirable host from the area, while in most cases, the problem is not serious enough to warrant treatment. However, fungicide treatment may be required in nurseries and other settings. Infection may be seasonal, thus requiring treatments for a limited period only.
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