Landscape shrubs can fall victim to a range of diseases characterized by a variety of symptoms including yellowed or deformed leaves, damaged bark and poor growth. Narrow your diagnosis by eliminating common shrub pests and inappropriate growing conditions. Once you are satisfied that your shrub is not being eaten by bugs, rodents or deer or starved for water, air, food or light, you can more easily identify shrub disease.
Eliminate Pests and Poor Conditions
Eliminate warm-blooded pests as a source of damage. Deer, rabbits and rodents can damage shrubs. Look for gnawing marks on the trunk, which indicates rabbits and rodents, or stripped leaves, which indicates deer. Dog urine can cause yellowed, dying leaves on the sides of your shrubs.
Inspect closely for insect infestation. Some insects are large enough to be seen happily nibbling on leaves and twigs, but many insect pests are quite small. Scale insects, spider mites and aphids can cause leaf drop and deformity despite their miniscule size. Use a magnifying glass to inspect the top and bottom surfaces of leaves.
Look at the growing area. Most shrubs are happiest in well-drained soil. Other common environmental problems include the incorrect amount of sun or shade, too little water and wind or freeze damage.
Identify The Shrub Disease
Identify your shrub. Some diseases affect only one type of plant. This will narrow your options.
Make note of the plant's specific symptoms. The University of Missouri and Kansas State University Cooperative Extension recommend a thorough examination of the shrub to including the trunk, leaves, branches and roots. Leaf spots are something to look for, as well as cankers, galls, decay, wilting, running sap, and unusual leaf formations, such as cupping.
Research common shrub diseases and compare the results to your observation. Vascular wilts will cause twigs and branches to die back and leave behind a black or brown ring where the branch died. Powdery mildew is a fungal growth that leaves a characteristic white powder on leaf surfaces. Cankers and galls are caused by fungi and bacterium and affect the bark of woody perennials.
Treat your shrub. Most shrub diseases are managed by pruning and/or the application of an appropriate fungicide.
Contact your state agricultural extension if you need more information about diagnosis or treatment. They can inspect a sample of your damaged or diseased shrub and help you make an accurate diagnosis. Cut a sample from your shrub and place it in a sealed plastic bag. Refrigerate the sample if you are unable to deliver it immediately. For the best results, provide as much information as possible.