[Illustration: Defoliation of sycamore tree caused by sycamore
anthracnose.]
Sycamore anthracnose, caused by _Gnomonia veneta_, is common on American
sycamore throughout its range in the eastern United States.
Anthracnose is a disease characterized by distinctive limited lesions on
stem, leaf, or fruit, often accompanied by dieback or blight and usually
caused by fungi that produce slimy spores that ooze from small
cup-shaped fruiting bodies that are visible with a hand lens. This
disease has four distinct symptom stages identified as twig blight, bud
blight, shoot blight, and leaf blight. Twig blight appears before leaf
emergence and kills the tips of small one-year-old twigs. Infection
comes initially from leaf litter and twig cankers. The second stage, bud
blight, develops during bud expansion in April and early May. Shoot
blight, the most frequently observed symptom, causes the sudden dying of
expanding shoots and also young leaves. Leaf blight, the final stage,
involves the actual infection of expanding or mature leaves. Diseased
portions of the leaf involve irregular brown areas adjacent to the
midrib and veins which are dotted with diseased spots. Incidence of
anthracnose is directly related to the amount of spring rainfall. Shoot
blight is severe if the weather for two weeks after leaf emergence is
cool and moist. The disease may defoliate trees, which usually put out a
new crop of leaves by late spring or summer.
Control of sycamore anthracnose under forest conditions is not
economically feasible. Where the disease is prevalent, other species
should be favored during thinnings. In shade and ornamental trees,
pruning of infected twigs, burning of leaves, and fertilization will
reduce the disease impact.
[Illustration: Leaf and twig symptoms.]