Importance. -- Severely affected oaks may be defoliated by midsummer,
which reduces growth, predisposes trees to other diseases and makes
the trees unsightly. White oaks are most severely affected. Anthracnose
does not result in major losses in forests.
the Fungus. --
Small, black, cushion-like, fruiting bodies form on necrotic tissue
where spores are produced. A beaked, flask-shaped, fruiting structure
can be found on dead leaves.
the Injury (figure 67). --
Round to irregular, lightbrown to black areas appear on the leaf, most
frequently along veins. Affected leaves often appear scorched, and may
curl or twist and drop from the tree. Infrequently, cankers and dieback
occur on small twigs.
The fungus overwinters in dead leaves. Spores (ascospores) are wind-blown
to the new, expanding leaves and shoots. Another spore type (conidia),
which reinfects other leaves or shoots, is then produced.
Collect and dispose of fallen leaves and twigs. Reduce the density of
branches to increase air movement. Fertilize to increase vigor and use
fungicide sprays as needed.