Peach Leaf Curl
· Apricot · Peach · Almond
Symptoms usually appear soon after leaf burst. Leaves become thickened and severely distorted with a puckered, crumpled or curled limb and a reddish to purple discoloration, depending on the variety of tree. As the infection progresses, the affected leaves take on a whitish-gray, powdery appearance as a result of the development of a fungal bloom on their surface. The gray covering gradually turns black, a process that coincides with higher daytime temperatures. Eventually, the diseased leaves die and fall, leading to defoliation and loss of vigor. They are soon replaced by new leaves emerging from the same growing point. Areas of bark or whole shoots can also be blackened when the infection becomes systemic, that is, when the fungus starts to spread within the plant internal tissues. In those cases, growing tips produce abnormal lateral shooting and the development of witch's brooms. On heavily diseased trees, the surface of fruits shows a dramatical change in appearance.
The symptoms are caused by the colonization of the plant tissues by the fungus Taphrina deformans. Spores produced on the leaf surface are washed by rain splashes or blown by wind onto peach twigs and buds, initiating new infections. The spores germinate during periods of frequent rain as the buds open in the spring and infect the still unfolded leaves. From the moment the spore enters the leaf bud, there are no effective countermeasure to stop the infectious process. If rain does not occur at this time, the spores remain inactive and little or no infection occurs. Lodged in bud scales or crevices in the bark throughout the summer and following winter, they eventually germinate during the next season. The fungus is only active at temperatures up to 16°C and can only reproduce at these low temperatures. Taphrina deformans infects peaches and nectarines, also almonds and occasionally apricots and ornamental Prunus.
Fungicidal sprays containing organic copper compounds like Bordeaux mixture can be used to combat effectively this fungus. Treatment should be applied once after the fall in autumn and again before the buds start to swell in spring. Note that repeated use of copper products can result in a buildup of copper in the soil, which eventually can become toxic to soil organisms.
Always consider an integrated approach with preventive measures together with biological treatments if available. Fungicides containing copper oxychloride, cupric hydroxide, thiram, ziram, chorothalinol or difenoconazole can be used. Treatment should be applied once after the fall in autumn and again before the buds start to swell in spring.