Citrus diseases

Page last updated: Wednesday, 22 July 2020 - 5:49pm

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This web article describes the most common diseases of citrus trees and their control using natural or low-toxic methods.

Unfamiliar diseases should be reported to the Pest and Disease Information Service (PaDIS) as these diseases could cause significant problems for our primary industries and environment if they were to become established in Western Australia.

Diseases of root and trunk

Armillaria root rot

Citrus trees affected by Armillaria root rot show decline with leaf yellowing and leaf drop. They may set a very heavy fruit crop in spring but collapse and die when the weather gets hot in summer.

Armillaria appears under the bark of affected trees as fan-shaped mycelia mats with a strong mushroom odour.

Mushroom-like funghi of Armillaria.
Mushroom-like funghi of Armillaria.

Long, thin, black strands (rhizomorphs), which look like shoelaces, spread the infection from root to root and plant to plant as they grow through the soil. Originally this fungus was a mild parasite on native trees, stumps and old roots.

In autumn, honey-coloured clusters of mushrooms which are the fruiting bodies of the fungus, appear around the bark of infected trees.

To avoid the disease, clear all remaining stumps and roots well ahead of planting time. To control the disease, isolate infected trees by deep trenching, which breaks the rhizomorphs. If trees are in the early stages of attack, treat them by exposing the roots to air at a distance of 60cm around the butt. Cut off and burn damaged roots.

Do not replace the soil for several years.

Badly affected trees, including the roots, should be removed and burned.