What is Armillaria Root Rot?

Armillaria root rot is a severe fungal disease that affects trees, woody plants, and some herbaceous plants including palms and succulents.

Also known as oak root fungus, Armillaria root rot can rapidly kill trees and presents a challenge to management since infected woody roots can persist for years underground. No plants are completely immune to Armillaria root rot, so prevention is key. Deeply planted trees are often more susceptible to this disease.

The distinctive “honey mushrooms” growing from the base of a tree signals an infection, but they may not always be present. Other visible symptoms include flat cankers on the trunk, wilting, and canopy...

[From the August 2016 issue of the UC IPM Green Bulletin]

Two “sap flux” diseases observed in landscape trees—bacterial wetwood (or slime flux) and alcoholic (“foamy”) flux—often trigger demands that a landscaper “do something.” Yet the most appropriate action may be to provide cultural care and to monitor for any additional problems rather than to apply chemicals or undergo drastic “tree surgery.”

Symptoms

A single wound or bark crack located on the trunk or a large branch...

[From Dec 2013 issue of the UC IPM Green Bulletin newsletter]

Pruning in Practice

Pruning is perhaps the most common tree maintenance activity that is undertaken on urban and ornamental trees. This is in sharp contrast with forest trees, which are pruned only in exceptional cases and yet grow and develop their mature form quite well, living considerably longer than urban trees. This tells us that trees do not require pruning in order to survive. Nevertheless, in ornamental landscapes, pruning can be beneficial for maximizing the benefits of trees, and in young trees pruning...