| Guignardia blotch is a foliage disease of many
Aesculus species, including California, Ohio, red,
and yellow buckeye and common, red, and
Japanese horse chestnuts. Bottlebrush buckeye (A.
parviflora) and some varieties of Ohio buckeye (A.
glabra varieties arguta, monticola, and sargentii) may
be resistant.
The leaves of affected plants develop large reddish
brown blotches surrounded by yellow tissue, often
causing the foliage to curl and brown. In severe
cases, leaves may fall prematurely in late summer.
Since the foliage is usually not badly damaged until
after the tree has completed much of its annual
growth, the disease is primarily aesthetic.
Wet weather promotes the growth of Guignardia
blotch. In the United States, this fungal disease only
occurs east of the Great Plains, perhaps because of
the drier conditions of the West. This disease may
become severe in nurseries or in plantings where
tree crowns are close together.
Symptoms and Diagnosis
Guignardia blotch first appears as water-soaked
irregular areas. These enlarge quickly and in a few
days are reddish-brown to brown leaf spots with
clear bright yellow margins. The blotches vary in
size and may frequently grow together, covering
large areas of leaf tissue. This causes the leaf to curl
and brown, becoming dry and brittle, and may
cause early leaf drop. Fruiting bodies of the fungus,
seen as black pinhead-sized specks, may be visible
in the lesions. Occasionally petioles and immature
fruit may also have small reddish brown lesions.
Symptoms of this disease are similar to those of
environmental leaf scorch. Leaves affected by scorch
will be on the sunny or windy side of the tree while
Guignardia blotch may affect most leaves. Scorched
leaves will not have the black fruiting bodies. See
also “Scorch of Trees and Shrubs”.
Life Cycle
The Guignardia fungus overwinters on fallen
Aesculus leaves. In early spring, its fruiting bodies
mature and during wet weather, they release spores
into the air. If the spores land on newly developing
susceptible leaves that remain wet for several hours,
the leaves become infected, resulting in blotches
within 10–20 days. New fruiting bodies develop in
early June and in wet weather, more infections may
continue throughout the summer.
Integrated Pest Management Strategies
1. Sanitation. Rake and dispose of infected leaves.
2. Pruning. Thin the tree canopy to improve air
circulation and to speed drying of leaves.
3. Fungicides. Chemical treatment is usually not
necessary or recommended in the home
landscape. Serious damage may be controlled by
applying a fungicide containing chlorothalonil or
mancozeb at bud break and then repeating the
application at 10 to 14 day intervals as long as
wet conditions continue. |
