Peach Leaf-Curl

Agdex#:	212/634
Publication Date:	10/83
Order#:	83-071
Last Reviewed:	10/83
History:	Not Available
Written by:	WP Roberts - OMAF

Table of Contents 

1. Introduction
2. How to Recognize the Disease
3. Injury
4. Cause
5. Factors Favouring the Disease
6. Control

Introduction

Peach leaf-curl is a potentially serious disease of peach and nectarine trees, and is the most frequently encountered disease of peach in the home garden. Peach leaf-curl received its name due to the characteristic shape of the infected leaves, but is also known less frequently as "curl" or "leaf blister."

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How to Recognize the Diseases

Peach leaf-curl affects leaves, tender growing shoots (Figure 1) and, more rarely, blossoms and fruit (Figure 2). The diseased leaves are either noticeably reddened or paler in colour than normal, and become curled or distorted. The leaves also become greatly increased in thickness and of a firm consistency. This condition is referred to as "blistering" (Figure 3). Only a few leaves of a tree may be affected, or the infections may be so numerous as to involve almost the entire foliage. As the season progresses, the red colouration becomes less pronounced and a greyish or powdery coating (the spores) appears over the upper surface of the leaves. The leaves gradually turn brown, wither and fall from the tree in the latter part of June or early July. Following the loss of leaves, a new set will be produced from dormant buds. Young terminal shoots may sometimes be affected and are reduced in length, appear swollen, pale green or yellow in colour, and produce only curled leaves.

Figure 1: Terminal peach shoot infected, showing brown withered leaves. Photo: T.R. Davidson, Agriculture Canada.

Figure 2: Young developing peach fruit infected with peach leaf-curl. The fruit on the leaf is a normal, healthy fruit. Photo: T.R. Davidson, Agriculture Canada.

Figure 3: Advanced infection or "blistering" on peach foliage. Photo: T.R. Davidson, Agriculture Canada.

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Injury

The injury from peach leaf-curl may be summarized as:

1. Loss of foliage in the early spring.
2. Death of trees due to repeated loss of foliage. This generally takes a period of approximately 3 to 5 years.
3. Terminal twigs may die back.
4. Blossoms may fail to set fruit or the young fruit may drop.
5. Fruit set may be reduced or prevented in the following year.
6. Affected trees are more susceptible to winterkill.

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Cause

Spores of the fungus (Taphrina deformans) are produced on the infected peach leaves and become lodged on the twigs, where they remain throughout the summer, fall and winter. In the following spring, the spores are washed into the opening buds. Infection occurs mainly during a short period when the leaf buds are breaking dormancy and starting to swell and open. As the leaves grow and mature, they are less susceptible to infection.

Factors Favouring the Disease

It has generally been observed that peach leaf-curl is favoured by cold, wet weather when the leaf buds are breaking dormancy and beginning to open. Temperatures of 10 to 15 degree C are favourable for infection, but at 21 degree C or above, if the leaves are growing rapidly, the fungus may die even though infection has started. Periods of heavy dews, light rainfall and early warm spring weather are unfavourable for the disease.

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Control

For effective control, one preventive spray should be applied. This should be applied in the late fall after all the leaves have fallen or in the early spring before buds break. Fall applications should be applied only after all the leaves have fallen; spray applied while leaves are still on the tree will result in severe burning of the leaves and poor coverage.

Treatments in the late spring after bud-break or in the summer are not effective.

Chemical control in commercial orchards is required each year. Growers should refer to the peach section in the current issue of Ontario Ministry of Agriculture, Food and Rural Affairs Publication 360, Fruit Production Recommendations.

Chemical control of peach leaf-curl can also be achieved by the home fruit grower. One preventive spray applied in the early spring before bud-break is recommended. The recommended materials for use by the home grower are ferbam or lime sulfur. The home grower should refer to the peach disease section in the current issue of Ontario Ministry of Agriculture, Food and Rural Affairs Publication 64, Insect and Disease Control in the Home Garden.

Some growers have reported that spraying does not always control the disease. These failures may be due to:

1. too-late applications of the fungicide
2. lack of the thoroughness of fungicide coverage
3. an ineffective choice of fungicide
4. weather conditions at the time of spraying or immediately following spraying.

Trees that have been defoliated by leaf-curl should be given the best of care and culture in order that they may overcome the effects of the disease.

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