of Rhode Island GreenShare Factsheets
Leaf 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.
Symptoms 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.
There 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 their tips.
Though rarely seen, flowers and fruit may also become diseased. They drop shortly
after infection. Diseased fruit has shiny, reddish, raised, warty spots.
The 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.
Adapted from Michael A. Ellis, Ohio State University
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information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program