Almond leaf scorch is a bacterial disease that kill otherwise healthy trees — or, if undetected and untreated, entire orchards — within just a few years. Learn to recognize the disease and take action early to save your trees and your livelihood

Connell, Joseph H

Teviotdale, Beth L

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UC Agriculture & Natural ResourcesFarmTitleAlmond Leaf ScorchPermalinkhttps://escholarship.org/uc/item/5kt594ccAuthorsTeviotdale, Beth LConnell, Joseph HPublication Date2003-06-01DOI10.3733/ucanr.8106 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUNIVERSITY OF CALIFORNIADivision of Agriculture and Natural Resourceshttp://anrcatalog.ucdavis.eduPublication 8106Almond Leaf ScorchBETH L. TEVIOTDALE, University of California Cooperative Extension PlantPathologist, Kearney Agricultural Center, Parlier; and JOSEPH H. CONNELL, Universityof California Cooperative Extension Pomology Advisor, Butte CountyThe bacterial disease known as almond leaf scorch presents a potentially seriousthreat to California almond orchards. The disease may be spread in the orchardby sharpshooter leafhoppers or spittlebugs, which feed in the xylem where wateris conducted through the tree. Within a few years, affected trees become unpro-ductive and may die. Early identification and elimination of diseased trees mayminimize the problem and effectively reduce further tree losses. This publicationhighlights disease symptoms and provides management suggestions.SYMPTOMSAlmond leaf scorch symptoms first appear on individ-ual leaves in early June to mid July. The tips or mar-gins of leaves initially turn light gray-green (fig.1).The scorching occurs with the onset of hot weather.By late July, symptoms are fully developed andare most noticeable (fig. 2). It is important to identifyand mark affected trees then, while the scorched areasof the tree canopy contrast clearly with healthy greenleaves. Once harvest begins, mites, dust, and droughtstress combined with tree shaking often make signs ofalmond leaf scorch difficult to detect.The disease develops slowly over several years,infecting more of the tree with each succeeding year(fig. 3). It may be easily overlooked when only a fewleaves on one branch are affected. Almond leaf scorch is also known as GoldenDeath because of the striking yellow color of a fully infected tree’s canopy. Thesetrees eventually die (fig. 4).Figure 1. Affected leavesdevelop a tan marginalscorch with a characteristcyellow band between thescorched and green portionsof the leaf. Figure 2. Patches of deadtissue may occur on leafmargins, and leaves oftencurl as they die. Entire leafblades may be affected.VARIETY SUSCEPTIBILITYAlmond leaf scorch is most common and severe in the Peerless variety, followed bySonora. Nonpareil is also susceptible and can be significantly affected. The disease israre in Carmel and Butte and is seldom seen in other varieties.PATHOGEN AND VECTORSAlmond leaf scorch and Pierce’s disease of grapevines arecaused by the same bacterium, Xylella fastidiosa. Insectscarry the pathogen from plant to plant, but tree to treespread of the pathogen has not been proven. The greensharpshooter, Draeculacephala minerva, and the red-headedsharpshooter, Carneocephala fulgida, are the most commonvectors of the pathogen found in almond orchards. Theglassy-winged sharpshooter, Homalodisca coagulata, maybecome even more successful at spreading the pathogen inalmond orchards because, unlike other known vectors, itprefers to feed on trees. The small, green potato leafhopper(Empoasca sp.), prune leafhopper (Edwardsiana prunicola),and the white apple leaf hopper (Typhlocyba pomaria) that commonly feed on almondleaves are not vectors of this disease.WHAT TO DONo chemical or nutritional treatments control almond leaf scorch. In addition, noresearch or practical experience suggests that disease occurrence is reduced by con-trolling the vectors with insecticides. If you suspect that a tree may be infected, firsttest its leaf tissue for excess salts, particularly chloride and sodium.Salt injury, particularly chloride burn, may be mistaken for almond leaf scorch.Sometimes the two are indistinguishable (fig. 5). Salt injury may occur atany time but often worsens asthe growing season progresses(fig. 6). Ordinarily it is a resultof excess salinity in soil orwater. Unlike almond leafscorch, salt injury affectsnumerous trees in one concen-trated area rather than individ-ual trees widely scatteredthroughout an orchard.If sodium and chloride lev-els are normal, and salinity hasbeen eliminated as a possible cause of the problem,contact your farm advisor to have the tree tested foralmond leaf scorch. The best time to test for almondleaf scorch is July through September. The best man-agement practice known now is to remove infectedtrees. The value of pruning out very early infections isunder investigation.2ANR Publication 8106Figure 3. Once a largebranch or two is infectedthe disease is more easilynoticed. Such infectionsmay have already beenpresent for more thantwo years.Figure 4. By the time symptomsengulf the entire canopy the treemay have been infected with leafscorch bacteria for 3 to 5 years.3ANR Publication 8106Figure 5. Salt burn is generally more concentrated atleaf tips than along margins, and it usually lacks theyellow band between the brown and green areas ofthe leaf that is characteristic of almond leaf scorch.Figure 6. Late season almond leaf scorch symptoms.4ANR Publication 8106FOR MORE INFORMATIONYou’ll find more information on plant diseases at these Web sites and in theseand other publications, slide sets, CD-ROMs, and videos from UC ANR:http://www.ipm.ucdavis.edu/PMG/selectnewpest.almonds.htmlhttp://www.cnr.Berkeley.edu/xylellaIntegrated Pest Management for Almonds, ANR Publication 3308(order from http://anrcatalog.ucdavis.edu)Pierce’s Disease, ANR Publication 21600 (order from http://anrcatalog.ucdavis.edu)http://ucce.ucdavis.edu/special/gwss/pubs.htmlPierce’s Disease, Glassy-Winged Sharpshooter online media kit(view at http://news.ucanr.org) An electronic version of this publication is available on the ANR Communication Services Web siteat http://anrcatalog.ucdavis.eduPublication 8106© 2003 by the Regents of the University of California, Division of Agriculture and NaturalResources. All rights reserved.The University of California prohibits discrimination against or harassment of any personemployed by or seeking employment with the University on the basis of race, color, national ori-gin, religion, sex, physical or mental disability, medical condition (cancer-related or genetic charac-teristics), ancestry, marital status, age, sexual orientation, citizenship, or status as a covered veteran(special disabled veteran, Vietnam-era veteran or any other veteran who served on active duty dur-ing a war or in a campaign or expedition for which a campaign badge has been authorized).University Policy is intended to be consistent with the provisions of applicable State and Federallaws.Inquiries regarding the University’s nondiscrimination policies may be directed to the AffirmativeAction/Staff Personnel Services Director, University of California, Agriculture and NaturalResources, 300 Lakeside Drive, 6th Floor, Oakland, CA 94612-3550 (510) 987-0096. For infor-mation about obtaining this publication, call (800) 994-8849. For downloading information,call (530) 754-5112.pr-6/03-AS/VJGThis publication has been anonymously peer reviewed for technical accuracy by University of Californiascientists and other qualified professionals. This review process was managed by the ANR AssociateEditor for Pest Management.

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