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Tree and Shrub Diseases

Iron Chlorosis

Leaves may become yellow, cream colored, or white, usually caused by reduced availability of iron in high pH soil. Correct the site-related conditions such as high soil pH, water logging, and poor aeration. Iron chelate applied to foliage may provide temporary greening, but for long term control, lower the soil pH.


Leaf Scorch

Leaf Scorch is a symptom that can occur any time the leaves need more water than they receive. It may be caused by diseases of the roots, crown and vascular system; cankers; inadequate available water; high air temperatures; damage to the roots from transplanting, soil compaction or excavation or natural gas leaks; chemical injury such as herbicides, excessive fertilizer and road salt; root girdling; “pot boundness” that occurred in containers before planting or following planting if roots fail to extend beyond the planting hole. Be sure soil is moist in the fall. Provide windbreaks around plants. Plant adapted varieties in sheltered locations or erect wind barriers.


Black Sooty Mold

Sooty mold is a name commonly given to a condition that is not truly a disease, but a black coating on leaves, branches and fruit made up of fungal growth.

Powdery Mildew

Powdery white moldy patches will appear on leaves. Remove badly affected shoots. Prune to thin out branches. Spray with fungicide when mildew appears.


Black Spot

Leaves will have black spots with irregular margins. Collect and remove fallen leaves.  A fungicide application may be necessary in spring as leaves expand.  For the best control, varieties that are susceptible to black spot must be protected with a fungicide before the disease is present.


Needles, twigs and smaller branches turn brown to reddish-brown as they gradually die back. Tiny black dots will appear later on infected parts. May be confused with normal fall browning, winter injury, spider mites, etc. Prune or remove blighted plants. A fungicide application may be needed.

Shoot Blight

Leaf Blight

Petal Blight

Twig Blight

Bacterial Blight

Fire Blight


Cankers are diseased areas of the bark. Many different kinds of fungi and a few bacteria may cause them. The outer bark may appear abnormal. Inner bark is brown and discolored. In time, the bark may fall off. Leaves beyond the canker may yellow, scorch or die. Usually canker-causing pathogens can infect only hosts that have been injured or stressed. Trees in decline often lose branches to cankers. Management of canker disease includes avoiding unnecessary injuries and knowing and supplying the maintenance needs of the host to reduce stress. Prune out diseased branches well below the visible infection. After each cut, disinfect pruning tools with rubbing alcohol or 10 percent household chlorine bleach in water. With Rhizoctonia/Phoma canker or “die back,” stems and leaves may become blackened or blighted. Shoots beyond the necrotic area wilt and die. Remove severely affected plants. It may be necessary to increase air circulation by pruning overhanging shrubs and improve drainage by amending soil.

Crown Gall

Use certified and disease-free stock from known suppliers or nurseries. Avoid nursery stock with galls. Avoid wounding stems or roots. Prune out and destroy affected plant parts. Use disinfectants on cut surfaces. Destroy severely affected plants. Carefully remove and destroy infected plants or plant parts. Avoid wounding. Use strict sanitation measures.

Leaf and Flower Gall

Leaves become thickened or fleshy galls that then turn pale green or white. The entire blossom may become a fleshy gall covered with a whitish bloom. Usually, chemical control is not warranted. Pick off and destroy galled parts, if feasible. If there is severe infection, apply the appropriate fungicide.

Root and Crown Rot

Root Rot can be caused by a wide number of fungi. Few of these can be controlled in the landscape, especially on large trees. With Phytophthora root rot, the leaves wilt. Growth is stunted. Fine roots decay and cankers may develop at the base of the stem. Fungicides are available, but their use generally is not recommended for established plantings. Remove and destroy affected plants. If practical, improve soil drainage and replant with a more tolerant variety.


Scab is serious in wet weather. Dull, olive-to-black velvety or scurfy spots will appear on leaves. Leaves may yellow and fall off. May also appear on fruit. Varieties vary in susceptibility.

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