[Illustration: Leaf symptoms of oak anthracnose.]
Oak anthracnose is caused by the fungus _Gnomonia veneta_. Trees of the
white oak group, particularly white oak, are susceptible to this
disease. Oaks throughout the entire eastern United States are affected
by the disease, although it is less common in the Northeast.
Infection occurs in the early spring or mid-summer. Symptoms on leaves
develop as irregular brown diseased areas (blotches) along the midrib
and the major side veins. These blotches may grow together by late
spring or early summer if infection occurs early. Blotches are usually
confined to the areas bordered by the larger veins. Leaves on the lower
branches are frequently killed and occasionally trees will be
defoliated. However, a second crop of leaves soon develops and mortality
is rare. Fruiting bodies of _Gloeosporium_, the imperfect fungus
fruiting stage of anthracnose, are located on the midrib and veins of
infected leaves. When the disease spreads to the twigs, cankers and
crown dieback may occur. The anthracnose fungus overwinters on diseased
twigs and in the leaf litter. Oak anthracnose has the same causal agent
as sycamore anthracnose, and the weather conditions favoring the
sycamore disease also increases the anthracnose on oak.
Control is similar to sycamore anthracnose and involves an integrated
program of pruning disease tissue, fertilization, and burning of leaf
litter. No practical control is available for forest trees.