Control PLANT DISEASE
For Better Farming And Better Living

Mimeo BP 2-9
January 1958

Leafspots of Shade Trees

Leafspot diseases of shade trees frequently cause the home owner worry and
concern. While leafspot diseases of shade trees are frequently conspicuous
and falling leaves in mid-summer are disturbing, the damage they actually do
is rarely as serious as the symptoms would suggest. There are many different
leafspot diseases of shade trees but those described below are frequently of
common occurrence in Indiana.

Catalna leafsnots
A number of fungi such as Cercosoora sp., Gloeosnorium sp., Phvllosticita
sp. and Alternaria sp. may cause leafspot diseases on catalpa. In wet springs
leafspot infections may occur on new foliage and appear as yellowish brown
to black areas that ultimately result in dead spots on infected leaves. Some
leaf fall may result from leafspot infections early in the season but de-
foliation rarely continues from this cause after mid-July. Catalpa leafspot
damage is usually most severe on the lower portions of the tree. Occasionally
secondary fungi will cause leafspots on catalpa late in the season. Such
infections occur only on trees in low vigor, are entirely secondary and do
not affect the vigor of the tree. Leafspots that occur in August or early
September on catalpa are of little consequence and should not cause concern
to the home owner.

Elm black spot
Black spot leaf disease of elms is caused by the fungus Gnomonia ulmea
and occasionally causes premature defoliation in wet seasons. Leaves in-
fected with black spot turn yellow early in the season and show small, notice-
able, shiny, coal-black spots scattered over the upper leaf surface. Damage
from this disease is occasionally severe on American elm and will cause
serious defoliation of Siberian elm in late June,

Horse chestnut leaf blotch
The fungus Guignardia aesculi may cause a conspicuous leafspot on horse
chestnut and occasionally on yellow buckeye. In late June or early July
small, irregular, reddish-brown spots with yellow edges will appear on in-
fected leaves. The spots gradually enlarge, run together and involve large
areas of the leaf causing it to curl and turn brown. Later on, small black
dots or spore-producing bodies will develop in the centers of the dead spots.
By early August infected leaves will appear as if they have been scorched
with fire and premature leaf fall may occur at this time. Leaf blotch is
very conspicuous and is frequently a cause for major concern. The damage
done by this disease is rarely serious, since trees are never killed and will
leaf out normally the following spring.

PURDUE UNIVERSITY Agricultural Extension Service, Lafayette, Indiana
Department of Botany and Plant Pathology, Life Science Building