Trees suffer from diseases in rain-soaked Midwest

Diseases affecting tree leaves are being found in sycamore, ash, crabapple and oak trees. Although these foliar diseases are often not the most life-threatening of plant diseases, they frustrate homeowners, said Janna Beckerman, a plant pathologist in Purdue University's Department of Botany and Plant Pathology.

"Otherwise healthy trees can tolerate several seasons of partial defoliation without suffering significant injury," Beckerman said. "In fact, trees produce such an abundance of leaves that some loss of foliage is not a major cause for concern."

She also said, however, that homeowners will be able to notice as little as 5 percent defoliation, and as little as 10 percent defoliation may cause homeowners to panic. While small amounts of leaf loss may begin to be noticed, Beckerman said that homeowners can't be certain their tree is suffering from disease until about one-third defoliation occurs.

Some examples of the more prominent diseases showing up in Indiana include sycamore, ash and oak anthracnose; apple scab; cedar-apple rust; plum pockets; and peach leaf curl.

Symptoms of the various forms of anthracnose consist of brown leaves, brown spots on leaves that spread down the mid-vein, or a loss of leaves.

Trees suffering from apple scab will have velvety brown to olive green spots on the leaves that later turn black, as well as black spots or cracks in the fruit itself. If the infection becomes severe, the trees may drop infected leaves.

If a homeowner finds large orange gelatinous galls on the stems of a juniper tree — also called Arborvitae — it may be suffering from cedar-apple rust.

Abnormally large and hollow fruit that is banana-shaped characterizes plum pockets, which is a disease caused by fungus. Curled, deformed leaves are a hallmark of peach leaf curl.

"If you suspect your plant has a disease, collect a section of the plant that shows both healthy and unhealthy tissue," Beckerman said. "This provides for a good comparison."

Beckerman said the best way to diagnose tree diseases with more certainty and to learn what can be done about them is to submit fresh plant samples for testing to the local Purdue Extension office, a nursery, or the Purdue Plant and Pest Diagnostic Laboratory. Once the sample is in the hands of experts, this testing will help determine the source of the problem and ways to counteract it.

Regardless of where the sample is submitted, be prepared to provide information such as where the plant is located, the type of plant, its exposure to the sun, any possible root disturbance, unique features and the degree of damage on the plant. To download a sample submission form, visit the Purdue Plant and Pest Diagnostic Laboratory Web site.

Writer: Jennifer Stewart, (765) 494-8402, jsstewar@purdue.edu

Source: Janna Beckerman, (765) 494-4614, jbeckerm@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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