How to Manage Pests

Pests in Gardens and Landscapes

Raywood ash canker and decline

Fraxinus oxycarpa 'Raywood' commonly is affected by this disease. Although trees usually are not killed, severely affected ash are often removed because of unsightly dieback, reduced shading, and their potential limb drop hazard.


Dieback of multiple branches throughout the canopy is indicative of Raywood ash canker and decline. Botryosphaeria stevensii can usually be isolated from the dead branches and is believed to contribute to the decline.

Life cycle

The Botryosphaeria stevensii fungus is a weak (secondary) pathogen. It is aggressive and damaging only when trees are stressed, such as by adverse growing conditions. Stressful site conditions and especially moisture deficit predispose Raywood ash to Botryosphaeria damage.


Raywood ash is apparently less drought tolerant than previously believed. Occasional deep watering during the drought season and pruning to thin canopies and reduce transpiration demand may improve the performance of Raywood ash.

Green ash, Fraxinus pennsylvanica, appears not to suffer from this problem. It is a similar-looking alternative for planting.

Ash leaves dying from Ash dieback
Raywood ash leaves dying from ash dieback

Limb cankers on Raywood ash
Limb cankers on Raywood ash

Statewide IPM Program, Agriculture and Natural Resources, University of California
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