Each year, the peach crop depends on whether or not we get a late freeze. As if that wasn’t bad enough, there are some maintenance practices that should be done early to ensure a good crop.

Producers often find themselves pruning and spraying in early spring only to have the whole peach crop ruined by a late freeze. By failing to spray prior to knowing whether the crop will survive the freeze, a grower could end up with a springtime disease known as peach leaf curl.

Peach leaf curl is caused by the fungus Taphrina deformans. The fungus survives the winter as spores (conidia) on bark and buds. Infection occurs very early in the growing season.

Symptoms of leaf curl first appear on developing leaves. They 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.

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. As the tissues mature they become resistant. 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 over winter until the next spring.

Environment can limit leaf curl infection. This partially explains why the disease does not occur every year. Leaf curl is worse when the weather is cool and wet. 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, but only weakly below 45 degrees. Rain is necessary for infection.

Though rarely seen, flowers and fruit may also become diseased. They drop shortly after they are infected. Diseased fruit has shiny, reddish, raised, warty spots.

When sprayed while dormant, peach leaf curl is not difficult to manage. Since the fungus survives the winter on the surface of twigs and buds, a single fungicide spray, 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.

There is no secondary spread of this disease from leaves infected in the spring to new leaves produces later in the growing season. Once infected leaves drop, no further symptoms will appear during that growing season. Disease twigs become swollen and stunted, and may have a slight golden cast. They usually produce curled leaves at their tips.

Peach leaf curl also affects nectarine trees but apricot trees are resistant.

Source - http://www.tahlequahdailypress.com/