Peach Leaf Curl

Integrated Pest Management for Home Gardeners and Landscape Professionals

Peach leaf curl, also known as leaf curl, is a disease caused by the fungus Taphrina deformans. Peach leaf curl af- fects the blossoms, fruit, leaves, and shoots of peaches, ornamental flower- ing peaches, and nectarines, and is one of the most common disease problems for backyard gardeners growing these Figure 2. Peach leaf curl symptoms can trees. The distorted, reddened foliage cause leaves to curl and distort. 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 Peach leaf curl as reddish areas on developing leaves. life These areas become thickened and puckered, causing leaves to curl and Figure 3. Though uncommon, symp- severely distort (Figs. 1 and 2). The Figure 1. Peach leaf curl symptoms typi- toms on fruit can occur, making the thickened areas turn yellowish and cal of a serious infection. surface corky and cracked. then grayish white, as velvety spores are produced on the surface by the leaf curl fungus. Later affected leaves turn leaf symptoms yellow or brown and can remain on the developing asci tree or may fall off; they are replaced conidium penetrates break through host tissue and leaf surface by a second set of leaves that develop produces an infection more normally unless wet weather young leaves in spring continues. The loss of leaves and the conidium germinating production of a second set result in de- new infection creased tree growth and fruit produc- REPEATING ascospores in asci tion. Defoliation in spring may expose CYCLE branches to sunburn injury. conidida overwinter conidium The peach leaf curl pathogen also in- on buds or twigs fects young green twigs and shoots. conidium budding ascospore ascospore Affected shoots become thickened, stunted, distorted, and often die. Only rarely do reddish, wrinkled to distort- Figure 4. Leaf curl disease cycle. ed (or hypertrophied) areas develop on fruit surfaces. Later in the season these infected areas of fruit become corky LIFE CYCLE and grow larger than normal, causing and tend to crack (Fig. 3). If leaf curl Leaf symptoms appear about 2 weeks swelling and distortion of the leaf. Red infection builds up and is left uncon- after leaves emerge from buds (Fig. plant pigments accumulate in the dis- trolled for several years, the tree may 4). The fungus grows between leaf torted cells. Cells of the fungus break decline and need to be removed. cells and stimulates them to divide through the cuticle of distorted leaves

EST OTES Publication 7426 PUniversity of California N Statewide Integrated Pest Management Program Agriculture and Natural Resources May 2012 May 2012 Peach Leaf Curl

and produce elongated, sac-like struc- ment when the tree is dormant is effec- to consumers. The most effective cop- tures called asci that produce sexual tive, although in areas of high rainfall per product, 90% tribasic copper sulfate spores called ascospores, which give or during a particularly wet winter, it with a 50% MCE (Microcop), is no lon- the leaf a grayish white, powdery or might be advisable to apply a second ger available to retail outlets, because velvetlike appearance. The ascospores spray late in the dormant season, pref- the manufacturer withdrew the prod- are released into the air, carried to new erably as flower buds begin to swell but uct in 2010, although remaining sup- tissues, and bud (divide) to form bud- before green leaf tips are first visible. plies still can be sold. conidia. Resistant Varieties The copper ammonium complex prod- The fungus survives the hot, dry sum- A few peach varieties are available that ucts can be made more effective by mer as ascospores and bud-conidia are resistant or partially resistant to adding 1% horticultural spray oil to the (asexual spores) on the tree’s surfaces. leaf curl. Currently available resistant application mix; the oil also aids in con- When the weather turns cool and wet varieties include Frost, Indian Free, trolling some aphids, scale insects, and in fall, the ascospores germinate to Muir, and Q-1-8. mites. Copper soap (copper octanoate) produce more bud-conidia. The new fungicides are also available, and pre- and old bud-conidia continue to in- The peach cultivar Frost is reportedly liminary research indicates they may crease in number by budding. Eventu- very tolerant but must receive fungicide provide some protection of trees. ally a film of bud-conidia is formed applications the first 2 to 3 years. Red- on the tree’s surface. In spring, the haven peach and most cultivars derived Be aware that repeated annual use of bud-conidia move by splashing water from it are tolerant to peach leaf curl, copper products over many seasons from irrigation or rain and can infect whereas Redskin peach and cultivars can result in a buildup of copper in new leaves. derived from it range from susceptible the soil, which eventually can become to highly susceptible to the disease. toxic to soil organisms, and if it moves Periods of cool, wet weather, when into waterways, can harm some leaves are first opening on the tree, There are fewer resistant nectarines, aquatic species. favor the disease. The optimum tem- although Kreibich is one such variety. perature for fungal growth in labora- Bordeaux Mixture. Copper sulfate tory cultures is 68°F, the minimum is Fungicides is not a fixed copper and, when used 48°F, and the maximum is 79° to 87° F. Copper. Historically, the most common- alone, is less effective than tribasic Budding of bud-conidia occurs at or ly used fungicides available to home copper sulfate or other fixed copper above 95% relative humidity. Wetness gardeners have been the fixed copper products. However, if copper sul- from rain, dew, or irrigation for more products. For all copper-containing fate is mixed with hydrated lime to than 12.5 hours at temperatures below products, the active ingredient, copper, make a Bordeaux mixture, the cop- 61°F is needed for infection. Maximum is listed as “metallic copper equivalent,” per sulfate and calcium in the lime infection occurs when trees are wet or MCE, on the label. Various product react together to form a fixed copper for 2 or more days. Although leaves formulations differ widely in their product that is effective against peach can be infected, symptoms might not metallic copper content. The higher the leaf curl. Bordeaux mixture is not appear if temperatures remain above MCE, the greater the amount of cop- available for sale; it must be mixed up 69°F. Cool weather prolongs the period per and the more effective the product just before application, and the ingre- of disease development by favoring will be. However, other factors such dients can be very difficult to find. For the pathogen and slowing leaf growth. as coverage, use of additives such as information on preparing Bordeaux Development of peach leaf curl ceases stickers and spreaders, and frequency mixture see Pest Notes: Bordeaux Mix- when young tissue is no longer devel- and duration of rain, which can wash ture in References. oping or when weather turns dry and off the copper, also will impact product warmer (79° to 87°F). effectiveness. In all cases, the copper Other Fungicides. The synthetic fungi- is active only when it is wet, when the cide chlorothalonil currently is the only MANAGEMENT copper ions are in solution. other noncopper fungicide available for To prevent peach leaf curl, use resistant managing peach leaf curl on backyard peach and nectarine varieties where Fixed copper products include tribasic trees. Lime sulfur (calcium polysulfide) possible. (See the Resistant Varieties or basic copper sulfate, cupric hydrox- products no longer are registered for section below.) For nonresistant variet- ide, and copper oxychloride sulfate backyard use. ies, treat trees with a fungicide every (C-O-C-S), but currently only liquid year after leaves have fallen. In cooler products containing copper ammo- Application. Thorough coverage with northern locations leaf fall usually is nium complex products with 8% MCE any fungicide is essential to obtain ad- in late November. In warmer southern (e.g., Kop R Spray Concentrate [Lilly equate disease control. Trees should be locations leaf fall can be as late as early Miller brands] and Liqui-Cop [Mon- sprayed to the point of runoff or until January. Generally a single early treat- terey Lawn and Garden]) are available they are dripping.

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When using pesticides, always read McCain, A. H., E. J. Perry, and G. W. Rossi, V., M. Bolognesi, L. Languasco, and follow the label for usage, rates, Hickman. 1979. Leaf curl fungicides. and S. Giosue. 2006. Influence of en- toxicity, and proper disposal. Proper Calif. Plant Pathol. 46:1–2. vironmental conditions on infection protective clothing and gear including of peach shoots by Taphrina deformans. goggles should be used when handling Moller, W. J., A. H. McCain, and D. H. Phytopathology 96:155–163. v any pesticides. Chaney. 1979. Leaf Curl Control in Peach- es and Nectarines. Oakland: Univ. Calif. Physical Controls Agric. Nat. Res. Leaflet 2613. Although symptoms of leaf curl are seen primarily in spring as new leaves Ogawa, J. M., E. I. Zehr, G. W. Bird, D. develop, there is little you can do to F. Ritchie, K. Uriu, and J. K. Uyemoto. control the disease at this time. Some 1995. Compendium of Stone Fruit Diseases. people remove diseased leaves or APS Press, St Paul, Minn. prune infected shoots, but this has not been shown to improve control. Nor- , Plant Pathology, University of California scientists and other mally, diseased leaves fall off within AUTHORS: J. C. Broome UC Davis/UC Cooperative Extension, Sac- qualified professionals have anonymously peer a few weeks and are replaced by new, reviewed this publication for technical accuracy. The ramento/Yolo/Solano Co.; and C. A. Ingels, ANR Associate Editor for Urban Pest Management healthy leaves, unless it is rainy. UC Cooperative Extension, Sacramento Co. managed this review process. To simplify information, trade names of products If a tree is severely affected with peach TECHNICAL EDITOR: M. L. Flint have been used. No endorsement of named products is intended, nor is criticism implied of similar products leaf curl this can stunt its growth, so EDITOR: M. L. Fayard that are not mentioned. consider thinning fruit later in the This material is partially based upon work supported by the Extension Service, U.S. Department season. Pruning in fall prior to apply- ILLUSTRATIONS: Figs. 1-3, J. K. Clark; and of Agriculture, under special project Section 3(d), ing any fungicides can reduce spore Fig. 4, V. Winemiller. Integrated Pest Management. numbers overwintering on the tree and reduce the amount of fungicide needed. Produced by UC Statewide Integrated Pest Management Program If leaf curl symptoms occurred on your University of California, Davis, CA 95616 trees in spring, be sure to treat the fol- This and other Pest Notes are available at lowing fall and/or winter to prevent www.ipm.ucdavis.edu. more serious losses the following year. For more information, contact the University of California Cooperative Extension office in your REFERENCES county. See your telephone directory for addresses University of California Broome, J. C. and D. R. Donaldson. June and phone numbers, or visit http://ucanr.org/ce.cfm. Agriculture and Natural Resources 2010. Pest Notes: Bordeaux Mixture. Oak- land: Univ. Calif. Agric. Nat. Res. Publ. WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations 7481. Also available online at www. given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed, ipm.ucdavis.edu/PMG/PESTNOTES/ away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans. pn7481.html. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. Flint, M. L. 1998. Pests of the Garden and Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either use the pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collection Small Farm: A Grower’s Guide to Using site. Contact your county agricultural commissioner for additional information on safe container disposal and Less Pesticide, 2nd ed. Oakland: Univ. for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that Calif. Agric. Nat. Res. Publ. 3332. they may contaminate water supplies or natural waterways.

Ingham, R., J. McMorran, C. M. Ocamb, NONDISCRIMINATION STATEMENT J. W. Pscheidt, and M. Putnam. 2010. The University of California prohibits discrimination or harassment of any person on the basis of race, Peach Leaf Curl. In Pacific Northwest color, national origin, religion, sex, gender identity, pregnancy (including childbirth and medical conditions related to pregnancy or childbirth), physical or mental disability, medical condition (cancer-related or Plant Disease Management Handbook: An genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or service in the Online Guide to Plant Disease Control. uniformed services (as defined by the Uniformed Services Employment and Reemployment Rights Act of 1994: service in the uniformed services includes membership, application for membership, performance of Corvallis: Ore. State Univ. Also avail- service, application for service, or obligation for service in the uniformed services) in any of its programs able online at http://pnwhandbooks.org/ or activities. plantdisease/. Accessed May 16, 2012. University policy also prohibits reprisal or retaliation against any person in any of its programs or activities for making a complaint of discrimination or sexual harassment or for using or participating in the investigation or resolution process of any such complaint. McCain, A. H. 1978. Peach leaf curl con- University policy is intended to be consistent with the provisions of applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be directed to the Affirmative Action/ trol for home gardeners in the San Fran- Equal Opportunity Director, University of California, Agriculture and Natural Resources, 1111 Franklin Street, cisco Bay Area. Calif. Plant Pathol. 43:4–5. 6th Floor, Oakland, CA 94607, (510) 987-0096.

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