Leaf curl

Leaf curl
Peach leaf curl
Causal agents	Taphrina fungi, Begomovirus
Hosts	peach, almond
Distribution	America, Europe, Asia, Africa, Australia, New Zealand

Leaf curl is a plant disease characterized by curling of leaves, and caused by a fungus, genus Taphrina, or virus, especially genus Begomovirus of the family Geminiviridae. One of the most notable types is peach leaf curl, caused by the fungus Taphrina deformans, which infects peach, nectarine, and almond trees. T. deformans is found in the United States, Europe, Asia, Africa, Australia, and New Zealand. It was first introduced in America in 1852 and has now spread all over the country.

Peach leaf curl reduces the amount of leaves and fruit produced by peach and nectarine trees. The disease costs the United States $2.5 to 3.0 million annually.

The fungus T. deformans causes deformed young leaves, red blisters, and ultimately the whitish bloom that covers the leaf as the infection progresses. This white color is made of asci that break through the cuticle of the leaf. One ascus consists of eight ascospores that create conidia, which are ejected in early summer and spread by rain and wind. The fungus survives the winter on the surface of the host plant, such as on bark or buds. In the winter, rainwater washes spores into the buds as they burst. Once this happens, no treatment is effective. In the spring, new leaves are infected by the conidia as the leaves emerge from the buds. The disease may not occur every year due to variation in temperature and rainfall. Specifically, for successful infection, the fungus requires cool and wet winters, where rain (not fog or dew) wets the tree for more than 12.5 hours at temperatures below 16 °C (61 °F).

...
Wikipedia