Cypress canker—Seiridium (=Coryneum) cardinale
Cypress canker, or Coryneum canker, primarily affects Cupressus spp. Leyland cypress is especially susceptible, as is Monterey cypress when planted away from the coast. The fungus occasionally damages arborvitae, Chamaecyparis, and junipers.
Identification
Resinous lesions form in infected bark and cambium. Infected branches or treetops turn yellow or brown and can become girdled and die. Often the entire plant is gradually killed.
Cypress cankers attract cypress bark moths, and their larvae feed and tunnel in cankered bark. These insects are secondary invaders, and their control is generally not warranted as it is the fungus that kills branches and trees, not this insect.
Life cycle
The fungus is moved by wind and within plants by splashing water. The fungus also can be moved on pruning tools and infected nursery stock. The pathogen enters trees through naturally occurring wounds or damaged tissue. Disease development is favored by prolonged periods of fog or light rain during moderate temperatures. Cankers enlarge faster on drought-stressed trees.
Solutions
Provide trees with proper care and prune off diseased branches. Plant species that are well adapted to local conditions and less susceptible to canker.
Instead of cypress, consider planting arborvitae (Platycladus and Thuja spp.) or (along the coast) incense cedar (Calocedrus decurrens), which resemble cypress but are less susceptible to or not affected by cypress canker. Avoid planting Leyland cypress in California. Do not plant Italian cypress or especially Monterey cypress in inland areas away from the direct local influence of the cool coastal climate.
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Cypress canker dieback on Leyland cypress
Cypress canker discolored, oozing bark
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