Fungal diseases on shrubs

Written by jenny harrington | 13/05/2017
Fungal diseases on shrubs
Keep shrubs healthy and disease-free. (Holly shrub. image by LiteWave from

Shrubs provide colour and structure to the home landscape. Whether you grow deciduous or evergreen shrubs, proper care is vital to prevent fungal diseases. Some fungal infestations kill shrubs, while others just render the plants weak and unattractive. Most fungal problems are avoidable if shrubs are planted correctly and properly cared for.

Root rots

Root rots stem from a variety of causes, most of them fungal. Affected shrubs may grow poorly, become stunted or stop producing new foliage and shoots. Root rots may be present for a year or longer before symptoms become apparent. Overly wet soils lead make plants susceptible to fungi that cause root. Avoid planting in poorly drained areas and do not overwater the shrubs. Occasionally, visible fungus may grow low on the trunk of affected shrubs, such as shelf fungi or slime mould. If you dig down to the roots, affected plants have soft, spongy roots that you can easily push your finger into.

Leaf spots

A variety of diseases cause leaf spots, and not all of them are fungal in origin. Fungal foliage diseases often cause brown or black spots that have a visible growth on them -- either slimy or fuzzy. Some fungal problems only attack the foliage and do not lead to plant death. Sometimes, leaf spots are a symptom of other fungal problems, such as root rot. If the spots do not return each year or only affect a few leaves, an overly wet or humid summer may have caused some temporary fugal growth. If overall decline of the shrub occurs, the fungal problem is in the roots. Prevent many forms of fungus that cause leaf spots by practicing proper irrigation and avoid wetting the foliage when watering. Pruning correctly also improves air circulation, which prevents may foliage fungal problems.


Mildews often only ruin the appearance of shrubs but don't lead to long-term health problems. Powdery mildew produces a grey or white powdery growth on foliage and stems. Severely infected leaves die off. Downy mildew produces similar growth, but the growth appears thicker and soft. Poor air circulation and too much moisture causes most mildew problems. Yearly pruning helps prevent the mildew from forming, as does proper watering. Prune out infested areas of the shrubs to help prevent the mildew from spreading, and remove all old plant matter from around the shrubs each year.

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