Peach Leaf Curl

by John Donan

Peach leaf curl is a disease caused by the fungus Taphrina deformans. Peach leaf curl affects the leaves and shoots of peaches, ornamental flowering peaches, and nectarines, and is one of the most common disease problems for backyard gardeners. The distorted, reddened foliage that it causes is easily seen in spring. When severe, the disease can reduce fruit production substantially. Taphrina deformans survives on tree surfaces and buds, and is favored by wet weather during spring.

The infection first appears in spring as reddish areas on developing leaves. These areas become thickened and puckered, causing leaves to curl and severely distort. The thickened areas turn yellowish gray and velvety as spores are produced on the surface by the leaf curl fungus. Affected leaves later turn yellow or brown and either remain on the tree or fall off; they are replaced by a second set of leaves that develop more normally unless wet weather continues. The loss of leaves and the production of a second set decrease tree growth and fruit production. Defoliation in spring may also expose branches to sunburn injury.

This fungus overwinters as dormant spores in bud scales and bark crevices. During cool, wet periods in early spring, these spores germinate and infect expanding leaves, and possibly twigs and young fruit. When a number of trees are planted close by, the new fungus spores which are later produced are in great numbers and are splashed or blown from tree to tree. These spores then remain dormant until the following spring. They do not infect mature leaves or fruit. Thus, disease development is limited to a brief period in the spring.

It can usually be controlled effectively with a single application of an appropriate fungicide. The timing of the fungicide spray is extremely important. The fungicide should be applied as a dormant spray, either in the fall after leaf drop or in late winter before buds begin to swell. Some of those found effective are ferbam, chlorothalonil (Daconil), Bordeaux, or liquid lime sulfur. This disease cannot be controlled once the leaves have started to expand. It is recommended that the home gardener consult either a certified nurseryman or licensed exterminator before applying any gardening chemicals. Also, read the label and follow the directions exactly.

In areas of high spring rainfall or when spring rainfall is abundant, it may be advisable to apply a second spraying in spring, preferably before buds begin to swell, but definitely before budbreak (when green color is first visible.)

If a dormant spray has been neglected, and disease develops, fruits should be thinned heavily to reduce the nutrient drain on the already weakened tree. Trees should be fertilized in the spring to promote new leaf growth and watered frequently throughout the growing season. However, do not over-fertilize or fertilize late in the season as this will stimulate succulent growth, which is very susceptible to winter injury.

Additional information can be found at

http://ucipm.ucdavis.edu/PMG/r540100311.html