UC IPM Home > Homes, Gardens, Landscapes, and Turf > Peach Leaf Curl

How to Manage Pests

Pests in Gardens and Landscapes

Peach Leaf Curl Revised 12/08 In this Guideline:
Identification and damage Life cycle Management About Pest Notes Publication Glossary

Peach leaf curl, also known as leaf curl, is a disease caused by the fungus Taphrina deformans. Peach leaf curl affects the blossoms, fruit, leaves, and shoots of peaches, ornamental flowering peaches, and nectarines, and is one of the most common disease problems for backyard gardeners growing these trees. The distorted, reddened foliage that it causes is easily seen in spring. When severe, the disease can reduce fruit production substantially.

IDENTIFICATION AND DAMAGE

Peach leaf curl 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 and then grayish white, as velvety spores are produced on the surface by the leaf curl fungus. Later affected leaves turn yellow or brown and can remain on the tree or may 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 result in decreased tree growth and fruit production. Defoliation in spring may expose branches to sunburn injury.

The peach leaf curl pathogen also infects young, green twigs and shoots. Affected shoots become thickened, stunted, distorted, and often die. Only rarely do reddish, wrinkled to distorted (or hypertrophied) areas develop on fruit surfaces. Later in the season these infected areas of fruit become corky and tend to crack. If leaf curl infection builds up and is left uncontrolled for several years, the tree may decline and need to be removed.

LIFE CYCLE

Leaf symptoms appear about 2 weeks after leaves emerge from buds. The fungus grows between leaf cells and stimulates them to divide and grow larger than normal, causing swelling and distortion of the leaf. Red plant pigments accumulate in the distorted cells. Cells of the fungus break through the cuticle of distorted leaves and produce elongated, sac-like structures called asci that produce sexual spores called ascospores, which give the leaf a grayish white, powdery or velvetlike appearance. The ascospores are released into the air, carried to new tissues, and bud (divide) to form bud-conidia. The fungus survives the hot, dry summer as ascospores and bud-conidia (these are asexual spores) on the tree’s surfaces. When the weather turns cool and wet in fall, the ascospores germinate to produce more bud-conidia. The new and old bud-conidia continue to increase in number by budding. Eventually a film of bud-conidia is formed on the tree’s surface. In spring, the bud-conidia move by splashing water from irrigation or rain and can infect new leaves.

Periods of cool, wet weather, when leaves are first opening on the tree, favor the disease. The optimum temperature for fungal growth in laboratory cultures is 68°F, the minimum is 48°F, and the maximum is 79° to 87° F. Budding of bud-conidia occurs at or above 95% relative humidity. Wetness from rain, dew, or irrigation for over 12.5 hours at temperatures below 61°F is needed for infection. Maximum infection occurs when trees are wet for 2 or more days. Although leaves may be infected, symptoms may not appear if temperatures remain above 69°F. Cool weather prolongs the period of disease development by favoring the pathogen and slowing leaf growth. Development of peach leaf curl ceases when young tissue is no longer developing or when weather turns dry and warmer (79° to 87°F).

MANAGEMENT

To prevent peach leaf curl, treat peach and nectarine trees with a fungicide every year after leaves have fallen. In cooler northern locations leaf fall is usually in late November. In warmer southern locations leaf fall is usually in early January. Generally a single early treatment when the tree is dormant is effective, however, in areas of high rainfall or during a particularly wet winter it may be advisable to apply a second spray late in the dormant season, preferably as flower buds begin to swell, but before green leaf tips are first visible.

Copper. The most commonly used, safest, and effective fungicides available to home owners are fixed copper products (Table 1). For all copper-containing products, the active ingredient is copper, listed as “metallic copper equivalent” or MCE on the label. Various product formulations differ widely in their metallic copper content. The higher the MCE, the greater the amount of copper, and thus the more effective the product will be. However, other factors like coverage, use of additives like stickers and spreaders, and frequency and duration of rain, which can wash off the copper, will also impact product effectiveness. In all cases, the copper is active only when it is wet, when the copper ions are in solution. Fixed copper products include tribasic or basic copper sulfate, cupric hydroxide, or copper oxychloride sulfate (C-O-C-S).

Bordeaux Mixture. Copper sulfate is not a fixed copper and, when used alone, is less effective than tribasic copper sulfate or other fixed copper products. However, if copper sulfate is mixed with hydrated lime to make a Bordeaux mixture, the copper sulfate and calcium in the lime react together to form a fixed copper product that is effective against peach leaf curl. Bordeaux mixture must be mixed up just before application. For information on preparing Bordeaux mixture see Pest Notes: Bordeaux Mixture in References.

The formulation of any of these copper products influences the effectiveness of the treatment. Fixed coppers can be mixed with agricultural spray oils to increase their persistence and efficacy; the oil also aids in the control of some aphids, scale insects, and mites. Do not use copper soaps (copper octanoate), which have a very low percent of copper (0.08%, which is 0.017% MCE) and are not labeled for control of peach leaf curl in the dormant season. Be aware that repeated annual use of copper products over many seasons can result in a buildup of copper in the soil, which eventually can become toxic to soil organisms, and if it moves into waterways, can harm some aquatic species.

Lime Sulfur and Other Fungicides. Other fungicides to use include calcium polysulfide, also known as lime sulfur, which is created when lime and sulfur are boiled together. It is caustic and rather foul-smelling, but a very effective fungicide. However, lime sulfur must be used immediately and not allowed to sit around after mixing as the sulfur can precipitate or separate out after a short storage time, which renders the fungicide ineffective. In addition, just enough of the product should be bought for the season, as it will lose strength after long storage times. The synthetic fungicide chlorothalonil is also available.

Application. Thorough coverage with any fungicide is essential to obtain adequate disease control. While lime sulfur and Bordeaux mixture are more effective than most fixed copper products used alone, home gardeners should be aware that lime sulfur is more hazardous to handle, being very caustic, and Bordeaux mixture is complicated to make. A fixed copper mixed with oil would be the best choice for most home gardeners.

When using pesticides, always read and follow the label for usage, rates, toxicity, and proper disposal. Proper protective clothing and gear including goggles should be used when handling any pesticides.

Physical Controls. Although symptoms of leaf curl are seen primarily in spring as new leaves develop, there is little you can do to control the disease at this time. Some people remove diseased leaves or prune infected shoots, but this has not been shown to improve control. Normally, diseased leaves fall off within a few weeks and are replaced by new, healthy leaves, unless it is rainy. If a tree is severely affected wtih peach leaf curl this can stunt its growth, therefore consider thinning fruit later in the season. Pruning in fall prior to applying any fungicides can reduce spore numbers overwintering on the tree and reduce the amount of fungicide needed. If leaf curl symptoms occurred on your trees in spring, be sure to treat the following fall and/or winter to prevent more serious losses the following year.

Resistant Varieties. There is a range of susceptibility to peach leaf curl in currently grown peach and nectarine cultivars with a few new peaches such as Indian Free, Q 1-8, and Muir considered tolerant to resistant to the disease. There are fewer resistant nectarines, such as Kreibich. The peach cultivar Frost is reportedly very tolerant, but must receive fungicide applications the first 2 to 3 years. Redhaven peach and most cultivars derived from it are tolerant to peach leaf curl, whereas Redskin peach and cultivars derived from it range from susceptible to highly susceptible to the disease.

WARNING ON THE USE OF CHEMICALS

REFERENCES

Flint, M. L. 1998. Pests of the Garden and Small Farm: A Grower’s Guide to Using Less Pesticide. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3332.

McCain, A. H. 1978. Peach leaf curl control for home gardeners in the San Francisco Bay Area. Calif. Plant Pathol. 43:4-5.

McCain, A. H., E. J. Perry, and G. W. Hickman. 1979. Leaf curl fungicides. Calif. Plant Pathol. 46:1-2.

Moller, W. J., A. H. McCain, and D. H. Chaney. 1979. Leaf Curl Control in Peaches and Nectarines. Oakland: Univ. Calif. Div. Agric. Sci. Leaflet 2613.

UC Statewide IPM Project. Oct. 2000. Pest Notes: Bordeaux Mixture. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 7481.

Ogawa, J. M., E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu, and J. K. Uyemoto. 1995. Compendium of Stone Fruit Diseases. APS Press, St Paul, Minn.

Pscheidt, J.W. and C. M. Ocamb 2008. Pacific Northwest Plant Disease Management Handbook. Oregon State University Online Guide to Plant Disease Control, Peach–Leaf Curl section. Accessed October 06, 2008.

Rossi, V., Bolognesi, M., Languasco, L. and Giosue, S. 2006. Influence of environmental conditions on infection of peach shoots by Taphrina deformans. Phytopathology 96:155-163.

PUBLICATION INFORMATION

Pest Notes: Peach Leaf Curl
UC ANR Publication 7426        

Authors: J. C. Broome, UC Cooperative Extension Sacramento, Yolo, and Solano, C. A. Ingels, UC Cooperative Extension, Sacramento.

Produced by UC Statewide IPM Program, University of California, Davis, CA 95616

PDF: You need a PDF reader, such as Acrobat Reader version 8 or later, to view or print this PDF. If no reader is installed on your computer, you can download a free copy of Adobe Acrobat Reader.

Top of page