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Species Page

anthracnose of dogwood

Discula destructiva

Distribution

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Host plants / species affected

Main hosts

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Cornus florida (Flowering dogwood)
Cornus nuttallii (Pacific dogwood)

List of symptoms / signs

Leaves - abnormal colours
Leaves - necrotic areas
Leaves - yellowed or dead
Stems - canker on woody stem
Stems - dieback
Stems - witches broom
Whole plant - plant dead; dieback

Symptoms

Initial symptoms are small leaf spots with a purple margin, which then develop into large necrotic blotches. In many cases, infected mature leaves die prematurely. Sometimes, they remain attached to the stems after normal leaf fall. Infection expands from leaves to small twigs and then branches. Twig and branch dieback start in the lower crown (hence the original name of the disease 'lower branch dieback'). Numerous epicormic shoots often form at the base of the trunk or on branches. D. destructiva causes cankers which can kill the tree. The fungus can kill trees of all sizes, but is more severe on young seedlings and understorey forest dogwoods.

Prevention and control

Control of the disease is difficult, particularly in forests. In parks and gardens, cultural control (adequate watering and fertilization, pruning, removal of fallen leaves) and chemical control can be used. In the USA, emphasis is given to: optimum fertilization, trickle irrigation, adequate sunlight, mulching, pruning, fungicides, resistant cultivars, limiting movement of nursery material (Daughtrey et al., 1996). Forest management techniques favourable to the survival of understorey dogwoods remain to be worked out, but Britton et al. (1994) suggest that anthracnose is less severe on stands which were clear-cut 30 years ago than on those where timber was only partially harvested.

Phytosanitary measures

No international measures are currently applied for D. destructiva. As the main risk of introduction is by movement of infected plants for planting, it would be appropriate to require such material to come from a pest-free area or pest-free place of production.

Impact

In the USA, in addition to the environmental impacts, consecutive years of infection have killed many ornamental Cornus spp. in parks and gardens. The disease now presents a considerable problem for nursery production of healthy plants.