March 2014 Plant Disease Update

Leaf blisters are a group of diseases caused by fungi in the genus Taphrina. These fungi produce their spore-bearing structures in clusters on the leaf surface of susceptible plants, such as peach, oak, elm and other tree species, in the early spring. Infected areas of the leaf pucker outward and form a visible “blister”. The thickened, blistered areas are a different color than the normal green of the rest of the leaf.

Peach leaf curl disease.
Severe blistering of peach leaves with peach leaf curl disease
Magnified Oak Leaf Blister Pathogen
Magnified cluster of spore-producing structures of the oak leaf blister pathogen.

On oaks and elms, blisters are initially light green; on peach, they may be light green or tan to pink or red. Later in the season, the blisters may turn brown and leaves may drop. In severe infections, which can occur during wet springs, leaves become severely distorted. This is especially evident on peach trees, hence the Latin name for the peach leaf curl pathogen: Taphrina “deformans”.

Oak Leaf Blister
Blistering of willow oak leaves due to oak leaf blister.

On ornamental trees, the disease does not usually warrant control measures. However, on peach trees, the disease can cause a significant reduction in yield. The pathogen infects not only the leaves, but also the fruit of peach trees, causing fruit distortion. One application of a registered fungicide, such as lime sulfur or Bordeaux mixture, during November or early spring before bud break will control the disease. By the time the symptoms are noticed later in the growing season, it is too late for effective use of fungicides.