Symptoms and Signs
Oxyporus wood rot appears first as a white fungal growth around the base of an affected tree in late summer. The growth, which is made up of fungal fruiting structures, extends for a short distance up the trunk and out into the soil. Ganoderma, Phellinus, and Trametes species produce fruiting structures that appear as conks or shelf-like brackets on the trunk or branches. By the time fruiting structures appear, the wood-rotting fungus is well established in the inner structural tissues of the tree. Although the tree is still productive and may appear perfectly healthy otherwise, it will probably fall over during a windstorm because the interior wood of the tree is weak, soft, and decayed.
Comments on the Disease
Damage by wood-decay fungi may be the leading cause of premature orchard decline. Oxyporus latemarginatus is also found on cherry; species of Ganoderma, Phellinus, and Trametes are found on almond, cherry and peach. These fungi cause white-rot decay. Another fungus, Laetiporus sulphureus, causes a brown rot of wood. Both white and brown rots lead to limb breakage or uprooting of trees during windstorms or mechanical harvesting.
Most wood rots are secondary diseases that invade only injured or dead tree tissue. The best way to protect a tree from wood-rot fungi is to
- follow recommended cultural practices to maintain vigorous trees,
- protect against crown gall,
- use careful soil and water management to avoid crown and root problems, and
- take steps to avoid mechanical injuries and sunburn.
The incidence of wood rots is higher in orchards irrigated with sprinklers; if you use sprinklers, avoid wetting tree trunks as much as possible. Do not apply pesticides for wood-rotting fungi. Destroying the conk or the white fungal growth at the base of the tree, is useless—the fruiting bodies are only an indication of extensive inner rot.
Remove and destroy diseased wood. When a tree falls over and is removed, no treatment is necessary for wood rots before planting another tree in the same spot; the fungi are not a threat to healthy young trees. However, if other disease organisms or nematodes are present in the soil, a preplant fumigation may be necessary. Crown-gall infections are implicated in increasing the incidence of wood rots because the dead portion of the gall is a natural infection site for wood rots. Take precautions to prevent crown-gall infections when new trees are planted.