curl is a springtime disease that occurs on peach, nectarine and
related ornamental plants. The disease, though not a problem every
spring, can be severe during cool, wet springs following mild winters.
The leaf curl fungus damages peach trees by causing an early leaf
drop. This weakens the trees, making them more susceptible to other
diseases and to winter injury. Weakened trees also will produce
fewer fruit the following season. Yield may be further reduced when
blossoms and young fruit become diseased and drop.
of leaf curl appear in the spring. Developing leaves become severely
distorted (thickened and puckered) and have a reddish or purple
cast. Later, as spores form on the leaf surface, the leaves become
powdery gray in color. Shortly after this, the leaves turn yellow
or brown and drop.
curl symptoms on peach leaves. Photo from the Iowa State Extension.
is no secondary spread of this disease from leaves infected in the
spring to new leaves produced later in the growing season. Once
infected leaves drop, no further symptoms will appear during that
growing season. Diseased twigs become swollen and stunted, and may
have a slight golden cast. They usually produce curled leaves at
Though rarely seen, flowers and fruit may also become diseased.
They drop shortly after infection. Diseased fruit has shiny, reddish,
raised, warty spots.
peach leaf curl fungus survives the winter as spores (conidia) on
bark and buds. Infection occurs very early in the growing season.
During cool, wet spring weather the conidia infect new leaves as
they emerge from the buds. Host plant tissues are susceptible for
only a short period; the tissues become resistant as they mature.
The fungus produces another type of spore (ascospore) on the upper
surface of the diseased leaves. During wet weather, ascospores produce
additional conidia by budding. These conidia are carried to other
parts of the tree by rain and wind, where they will overwinter until
the next spring. Environmental conditions can limit leaf curl infection,
which helps to explain why the disease does not occur every year.
Low temperatures are thought to retard maturation of leaf tissue,
thus prolonging the time infection may occur. The fungus can penetrate
young peach leaves readily at temperatures between 50 and 70 degrees
F, but only weakly below 45 degrees F. Rain is necessary for infection.
Leaf curl is not difficult to control. Since the fungus survives
the winter on the surface of twigs and buds, a single fungicide
spray--such as lime sulfur or a copper-based fungicide--thoroughly
covering the entire tree, will provide control. If leaf curl does
result in significant defoliation in the spring, the fruit on affected
trees should be thinned to compensate for the loss of leaves. Over-cropping
the tree will weaken it and make it more susceptible to winter injury.
Michael A. Ellis, Ohio State University Extension, 1999