Leaf curlers is pathogenic fungus that infects fruit trees. Taphrina deformans, the scientific name for the fungus, causes reddish areas on developing leaves, making them thicken and curl or become distorted. New shoots that are infected become thickened, stunted and often die. Fruit is affected late in the season--as it ripens, it will begin to crack. It affects not only the leaves but the blossoms and fruits. There are no symptoms during the dormant season of fruit trees; symptoms only begin appearing in the spring as new growth appears. Severe cases reduce fruit production. Left untreated, the infected trees will need to be removed because they will no longer produce fruit and will cause the fungus to spread to other trees.
Prune infected stems and branches at the first signs of infection. Heavily infected branches will need to be completely removed. Trim small stems and branches with light infection--you do not need to remove the entire branch. Remove infected fruit.
Prune trees as they enter the dormant period in late fall/early winter. Light pruning over the whole tree will expose spores that may have settled on the tree.
Apply a copper-based commercial fungicide after pruning. This will help decrease the number of viable spores over winter.