Chinese elm anthracnose—Stegophora ulmea
The disease affects Chinese elms, Ulmus parvifolia. Even vigorous Chinese elms may be girdled and killed by this fungal disease in coastal areas of California. Chinese elm anthracnose cankers are rarely a problem in warmer interior areas of California.
Identification
Chinese elm anthracnose causes irregular, black, tarlike spots on leaves, premature leaf drop, and twig dieback in Chinese elm. More serious damage results when anthracnose cankers form in limbs and trunks.
Life cycle
The disease cycle is initiated in the spring when new leaves are infected with ascospores from overwintered perithecia. Spores are released into the air following a period of wetness and germinate optimally at approximately 46°F. Infection can occur from spring onwards and be damaging in wet conditions. On evergreen Chinese elm, symptoms of the disease can be present all year.
Solutions
Prune infected branches back to the next healthy lateral. Cut out small cankers on the trunk and major limbs before they become large, but do not make large wounds. Around the entire margin of small cankers cut about 1/2 inch into healthy wood, which should allow wounds to close.
Consider replacing severely infected trees. The Brea and Drake cultivars of Chinese elm are less susceptible to anthracnose. Avoid Evergreen, Sempervirens, and True Green Chinese elms where anthracnose is a problem.
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Chinese elm anthracnose, or black leaf spots
Chinese elm anthracnose trunk cankers
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