Phytophthora Root Rot of Rhododendron

By The Old House Web

Phytophthora Root Rot of Rhododendron

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The roots of rhododendrons growing in wet soil are attacked and rotted by water molds.

Symptoms: Symptoms are wilting and death of the top of the plant. To diagnose the cause as root rot, examine the finer roots of plants just showing wilting. If the roots are black and soft and the outer skin easily pulls away from the inner wood, the likely cause of disease is a root rot fungus. Plants affected by root rot show an inward curling of the leaves. Drought alone, however, causes the same top symptoms. With root rot, a single branch near the soil surface may develop curled leaves, then die and drop its leaves. This branch dieback occurs when the root rot fungus is splashed up onto a leaf, infecting the leaf and the branch.

Cause: Root rot of rhododendron is often symptomless in the landscape until stress from drought or flooding brings on disease. Fertilizers are also important in predisposing the plants to disease. High amounts of nitrogen fertilizer are the most important factor in bringing about the root rot disease in the urban landscape.

Control: Plant in a well-drained site and take care to water during summer droughts. Avoid use of fertilizers; if needed, apply a low rate of slow release fertilizer. It is particularly important to not add high nitrogen rates at transplanting. Fungicides for controlling root rots are available for use as soil drenches.

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Phytophthora root rot on rhododendron - 33K Phytophthora root rot on rhododendron - 37K
Phytophthora root rot on rhododendron, branch dieback - 43K Phytophthora root rot on rhododendron, inner bark symptoms - 17K
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