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Disease and Pests

There are obviously too many disease and pests to be outlined here. At one time or another any tree or shrub will have disease or pest issues, many are insignificant.

Disease and insect pests attack plants in many different ways. Most of the diseases are due to fungi and they commonly cause damage to leaves, stems, limbs and fruits. Insects most often feed on the leaves or fruits of plants, but some, like scale, may be found on limbs.

Plants which simply are not growing well and there are no water or nutrient issues, may have disease of the root system. Many fungi can cause root diseases and present as “root rot”. Insects rarely cause root damage, but microscopic worms called nematodes very commonly damage roots of many types of ornamental and agricultural plants.

Control of the disease or pest problem depends on identifying the cause. OSU Master Gardeners can usually help with the diagnosis. They are available either on the phone or you may bring in a plant sample or photo.

When taking a photo or collecting a sample to take to the Extension Office, look carefully at leaves and stems for evidence of disease. If a sample of a limb is obtained, be sure to get an area with both disease and healthy parts, if possible. Also note whether the whole plant is involved, or the problem is isolated. Note if other species of plants nearby have similar involvement.

When the Master Gardeners are unable to make a diagnosis, The Plant Disease and Insect Diagnostic Laboratory (PDIDL) on OSU Stillwater campus almost always is able to do so. PDIDL web site is here. Samples may be sent to them directly, or through the Master Gardener office, if needed. The PDIDL web site has a form to fill out about your plant. There is no charge for emailed digital images. Charges do apply for physical samples mailed to the lab.

There are some useful websites which may help you with identifying and treating problems with trees and shrubs. Three are listed below.


National Arborists

Identifying Tree Diseases: North Carolina Extension

Disease Management Recommendations: University of Minnesota Extension