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English Oak with Bark Loss: Hypoxylon Canker

A 22-year-old English oak near San Francisco Bay has a football-sized barkless patch on a limb with dry, cracked wood. This suggests Hypoxylon canker, a stress-related disease. Prune off affected limb. Fertilize with 10-10-10 at 1 lb per inch trunk diameter now and mid-summer. Water during dry periods. Disease enters through stress; vigor is best defense.

Treatment

Remove cankered limb.
Fertilize and water to reduce stress.
Monitor for new cankers.

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