Recognizing Deciduous Tree and Shrub Diseases

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When you notice a problem with a deciduous tree or shrub, it is often difficult to tell at first glance if the problem is caused by a disease, an insect, or the environment. The important thing is to not jump to conclusions; a wrong diagnosis will not help your plant, and may even make the problem worse. A little time spent gathering information about the tree or shrub, and about where it is planted will help you to unravel some of the complexities of plant diagnosis. The key to successful diagnosis in plants is to be patient and never assume anything.

• First and foremost, what kind of plant do you have? Many diseases affect only specific trees and shrubs, so knowing the plant narrows the field of possible problems. Know what a healthy example of this plant looks like, and what the cultural requirements are for successfully growing it.
• Next, write down any information on cultural practices, weather conditions, and pesticides, fertilizers, and weed killer applications that occurred before and during the development of the symptoms. Along with this information, detail the physical characteristics of the site where the tree or shrub is planted. How old is the plant? What is the soil type? The drainage? Recent construction? Near the street? How often and how much do you water? Does the site provide protection from wind? Or is it fully exposed. How much sun does the plant receive each day, or is it mostly in the shade. After assessing the most recent conditions, think back to last year, or the year before, did anything out of the ordinary happen to the tree or shrub then? Sudden changes in temperature? Ice storms? Early or late freezes?
• Now, take a look at the entire plant and the area surrounding it. Is only this tree or shrub affected, or does other plant material (including same species trees or shrubs) exhibit the same symptoms.
• Where does the problem appear on the tree or shrub? All on one side? Only at the top? At the bottom only? Is the entire plant affected? The distribution of the problem is important in distinguishing between environmental problems, insect problems or chemically induced problems.
• Next, inspect the plant carefully in order to list the specific symptoms of the problem, and list everything unusual you see. You should inspect the trunk, leaves (upper and lower surfaces), branches, roots; look for leaf spots, insects feeding, cankers, galls, decay, wilting, sap running, wounds, unusual leaf formations, cupping of leaves, either upwards or downwards…
• Next, consult reliable sources, and compare your information with descriptions of problems known to occur on your plant. The Extension Office has numerous well-illustrated publications that can help you identify a problem correctly. But, if you are unsure, take a good size fresh branch sample that shows the problem in progress on your tree or shrub to your Cooperative Extension Office.

Once the problem is diagnosed, the proper control measures can be adopted.

Dennis Patton, DPatton@oznet.ksu.edu
County Extension Agent, Horticulture
Johnson County, Kansas
Kansas State University Research and Extension