Root rot is caused by various fungal diseases. One of the most serious is cinnamon fungus, Phytophthora cinnamomi.

In hot weather a healthy plant may partially or completely wilt and die within a few days.

Armillaria root rot spreads through the soil by means of flat, black cords that resemble shoelaces. Infected trees lose vigour, leaves yellow and branches die back from the tips. Clusters of honey- or golden-coloured toadstools appear at the base of dead trees or from roots remaining in the ground. They're produces from the source of infection of armillaria root rot.

Control:
The fungus may linger for years and it's necessary to fumigate the soil before replanting. Remove dead plants, including their roots. Drench the soil with an approved chemical, early application of which can save mildly affected plants.

In future, grow plant species that are tolerant of cinnamon fungus.