Fusarium Wilt of Canary Island Date Palm1 - University of Florida

PP-215Fusarium Wilt of Canary Island Date Palm 1Monica L. Elliott 2Summary• As the name implies, Fusarium wilt of CanaryIsland date palm is primarily observed onPhoenix canariensis (Canary Island date palm).• The disease is caused by the fungus Fusariumoxysporum f. sp. canariensis.• The leaf symptoms include a one-sided death,wherein the leaflets on only one side of therachis are desiccated or dead. This is oftenaccompanied by a reddish-brown or dark-brownstreak on the petiole and rachis on the same sideas the desiccated or dead leaflets. Eventually,the entire leaf dies.• The disease symptoms normally appear first onthe oldest (lowest) living leaves, and thenprogressively move upward in the canopy untilthe palm is killed.• The only other disease that these symptomscould be confused with is petiole/rachis blight.• Transmission of the fungus from palm to palmis primarily by contaminated pruning tools.• There is no cure for this lethal disease.Fungicides have not been effective againstFusarium wilt.• Since there is no cure, disease management isaimed at disease prevention. A new hand saw ora disinfected pruning tool should be used forpruning leaves from each individual CanaryIsland date palm.• A laboratory confirmation of Fusarium wilt,using molecular techniques, is stronglyrecommended for nursery situations.IntroductionUnlike most fungal diseases of palms, thisdisease is very host specific, with the primary hostbeing Phoenix canariensis (Canary Island date palm).It is caused by Fusarium oxysporum f. sp.canariensis. The name “Fusarium wilt of CanaryIsland date palm” was given to this disease todistinguish it from two other Fusarium wilt diseasesthat occur on palms, which are also very hostspecific. In Florida (and the U.S.), the name is oftenshortened to simply “Fusarium wilt.”1. This document is Fact Sheet PP-215, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food andAgricultural Sciences, University of Florida. Original publication date January 2006. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. M. L. Elliott, professor, Plant Pathology Department, Fort Lauderdale Research and Education Center--Ft. Lauderdale, FL; Florida Cooperative ExtensionService, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL.The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information andother services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex,sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service,University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. LarryArrington, Dean

Fusarium Wilt of Canary Island Date Palm 2"Fusarium wilt of date palm" (also calledBayoud disease) only occurs on Phoenix dactylifera,and thus far is restricted to Morocco and Algeria. Itis caused by Fusarium oxysporum f. sp. albedinis."Fusarium wilt of oil palm" only occurs on Elaeisguineenis and Elaeis oleifera, and thus far is restrictedto countries in Central Africa and South America. Itis caused by Fusarium oxysporum f. sp. elaeidis.Pathogen and HostsFusarium wilt of Canary Island date palm iscaused by the fungus Fusarium oxysporum f. sp.canariensis. It was first documented in the U.S. inthe 1970s in California, but was not documented inFlorida until 1994. The disease has been observed inAustralia, France, Greece, Italy and Japan.This fungus causes a vascular wilt of the palm.Specifically, it obstructs the xylem(water-conducting) tissue, which results in thesymptoms of desiccation and death described below.The fungus produces short-lived spores(macroconidia and microconidia). It also produceschlamydospores, spores that will live in the soil andplant tissue for long time periods (usually years).Because most of the root system is left behind after apalm dies from this disease, this mass of roots mayact as a reservoir for the fungus for long time periods.Experimental and observational evidencesuggests that other Phoenix species may besusceptible to this fungus, including Phoenixdactylifera (date palm), Phoenix reclinata (Senegaldate palm), and Phoenix sylvestris (wild date palm),but not Phoenix roebelenii (pygmy date palm).The disease has also been noted on Washingtoniafilifera (California fan palm) in one location each inCalifornia and Australia. Both these sites hadpreviously contained diseased Canary Island datepalms that died from Fusarium wilt. However, thefield diagnosis of Fusarium wilt-like symptoms onWashingtonia robusta (Mexican fan palm), a palmcommonly grown throughout Florida, can probablybe attributed to petiole/rachis blight. See the factsheet on this disease at http://edis.ifas.ufl.edu/pp145.From 1999 through 2004, the Florida ExtensionPlant Disease Clinic reported 71 palm samplespositive for Fusarium oxysporum f. sp. canariensis.Of these, 56 were Phoenix canariensis, 4 werePhoenix dactylifera, 1 was a Phoenix sylvestris, 5were unidentified Phoenix spp., 4 were palms ofunknown genera (information not provided whensample submitted), and 1 was a Washingtoniarobusta. Thus, in Florida, as for most of the world,the vast majority of palms diagnosed with Fusariumwilt have been Phoenix canariensis.Palm AnatomyTo understand the symptoms described below,the terminology regarding palm anatomy must bedefined. Phoenix species are an example of a pinnateor feather-leaf palm. The entire leaf is often called afrond. The leaf consists of a blade, a petiole and aleaf base. The leaf base is the broad section thatattaches to the trunk. The petiole is the “stem” ofthe leaf from the leaf base to the point where leafletsbegin to attach to it. On a feather-leaf palm, theextension of the petiole into the leaf blade where allthe leaflets attach is called the rachis. The leaflets areoften referred to as pinnae.SymptomsAlthough the name “Fusarium wilt” impliesthat the primary symptom will be a wilt, vascularwilts in palms do not cause wilt symptoms. Instead,they cause leaf desiccation and leaf death symptoms.As with any disease, a progression of symptoms isobserved with Fusarium wilt. Initial symptomsnormally occur on the lowest (oldest) living leaves.Leaflets, either all of them or only a portion, on onlyone side of the rachis will be discolored, usually ashade of brown due to desiccation or death. Theleaflets on the opposite side of the rachis will behealthy. This very distinctive symptom is oftenreferred to as a “one-sided wilt” or “one-sideddeath” (Figure 1). Eventually, the leaflets on theother side of the rachis will turn brown also, and theentire leaf dies.A reddish-brown or dark-brown streak or stripewill be observed on the petiole and rachis of theaffected frond, initially on the same side where thefirst dead leaflets appeared, and usually beginning at

Fusarium Wilt of Canary Island Date Palm 3Figure 2. Reddish-brown stripe on leaf petiole is on sameside that exhibited one-sided death of leaflets due toFusarium wilt. Credits: N.A. HarrisonFigure 1. One-sided death of leaflets is typical ofFusarium wilt. Credits: T.K. Broschator near the leaf base (Figure 2). This streak may runthe full length of the petiole and rachis, or just aportion of it. Internal discoloration will be observedin both cross-sections and longitudinal sections of thediscolored petiole and rachis (Figure 3). This internaldiscoloration is due to the fungus infesting the xylemtissue.The disease symptoms normally begin on thelowest (oldest) leaves and then move up the canopy,progressively killing younger and younger leaves(Figure 4). The palm may die relatively quickly(within months) or linger for a couple of years. Thereasons for this disparity is not known.Possible variations in symptoms include thedisease initially starting mid-canopy rather than at thebottom of the canopy. For some leaves, the leafletsmay begin turning brown at the leaf tip and on bothsides at once, rather than just on one side. It has alsoFigure 3. Longitudinal section of petiole illustrates thevascular discoloration due to infestation of xylem tissue byFusarium oxysporum f. sp. canariensis. Credits: G.W.Simonebeen noted that the presence of palm weevils in thebud of Fusarium wilt-stressed palms hasten thedecline of the palm, and may complicate determiningthe cause of the palm's decline.DiagnosisField diagnosis can often be made based on thesymptoms described above, especially if thesymptoms are typical ones. The only other diseaseFusarium wilt of Canary Island date palm might beconfused with is petiole/rachis blight. The latter isnot a true vascular wilt and usually does not kill thepalm, but the resulting individual leaf symptoms canbe very similar on a Phoenix species. See the factsheet on this disease at http://edis.ifas.ufl.edu/pp145.While a molecular laboratory diagnosis toconfirm the field diagnosis may not be a necessary

Fusarium Wilt of Canary Island Date Palm 4culture. Thus, isolation of a fungus that looks like F.oxysporum does not confirm the field diagnosis. Thefungus growing on the culture plate is then subjectedto a molecular test that is specific for F. oxysporum f.sp. canariensis.If the field symptoms appear typical forFusarium wilt, but the molecular test results arenegative, then there are two things to consider. First,the symptoms may not be an expression of Fusariumwilt, but may be an expression of petiole/rachisblight. Many of the petiole/rachis blight pathogensare not culturable from plant tissue. Second, thesymptoms may be an expression of Fusarium wilt,but a false negative was obtained from the moleculartest. No diagnostic test is perfect every time.Figure 4. Progressive death of leaves up through thecanopy due to Fusarium wilt. Note that the right side of theupright leaf at top of canopy is exhibiting the one-sideddeath of leaflets typical of Fusarium wilt. Credits: T.K.Broschatexpense for a landscape situation, it is critical if thedisease symptoms are occurring in a palm nursery.To confirm the field diagnosis, a laboratory mustisolate the pathogen from the affected leaf tissue andthen conduct a molecular test on the isolated culture.Currently, only the Florida Extension Plant DiseaseClinic in Gainesville conducts this molecular test.Contact your local county Extension office or theClinic for complete details on correct samplesubmission procedures and cost of a laboratorydiagnosis.Molecular confirmation of the isolated fungus iscritical. There are numerous Fusarium oxysporumisolates that do not cause disease, but may beassociated with palm material. Unfortunately, it isnot possible to separate pathogenic isolates fromnon-pathogenic isolates based on their appearance inThe next step would be to obtain new samplesfrom the diseased palm or similarly diseased palmand resubmit to the Clinic for the molecular test forF. oxysporum f. sp. canariensis and to confirmpresence or absence of petiole/rachis blightpathogens. Be sure to discuss the problem with theclinic staff before resubmitting samples. If nosymptomatic leaves are available, wait until newsymptoms develop before resubmitting.Disease ManagementThere are no cures for this disease. Fungicideshave been evaluated, but none have been effective.Disease management is based solely on diseaseprevention.The fungus is moved between distant locationsby plant material, both live plants and probably seed.This is probably how the disease was first introduced(and re-introduced) into Florida. Unpublishedresearch from both Florida and Australia havedemonstrated the fungus can colonize palm seeds.This makes it critical for palm nurseries to know thattheir seed source and stock plants are coming from adisease-free source. Likewise, nursery growers,landscape architects and installation companiesshould examine and select Canary Island date palmswhile they are still in the field or on site at a containernursery and make this inspection prior to anytrimming of older leaves so the plants can beinspected for symptoms. Then, either monitor thetrimming of these palms to ensure they are trimmed

Fusarium Wilt of Canary Island Date Palm 5correctly, or trim them at the installation site usingthe correct procedure discussed below.Once the disease is established in a landscape ornursery, the disease appears to primarily betransmitted from palm to palm via leaf pruningequipment (Figure 5). The fungal pathogen is in thevascular tissue of the leaf. Equipment used to removeleaves from an infected Canary Island date palm(chain saw, lopper, pruning shear, hand saw, etc.) willhave fungal-infested leaf material (wood dust, plantsap) on the blades. If that equipment is not cleanedand disinfected, the next Canary Island date palm(and perhaps other Phoenix species) pruned by thisequipment will be exposed to this fungal-infested leafmaterial.It is important to note that a palm could beinfected but appear healthy (symptomless) becausethe disease has not developed to the point that leafsymptoms are being expressed. Unfortuantely, we donot know how long this infected but symptomlessstage of the disease lasts. It could be 6 to 18 months.Thus, the fungus could still be moved from palm topalm by pruning infected but symptomless leaves!This means Canary Island date palms should bepruned with either new handsaws or clean,disinfected tools – both in the landscape and nursery.This applies to all Canary Island date palms, diseasedand healthy. Either a new handsaw or a clean,disinfected pruning tool should be used for eachindividual palm. Pruning should be limited to onceeach year. Furthermore, pruning should be restrictedto removal of only dead or dying leaves. Severepruning, such as “hurricane cuts” or “pineapplecuts,” weakens trees and increases the risk ofpathogen transmission. Pruning should be viewed asa risk factor for Fusarium wilt disease transmission,and not as a benefit to the Canary Island date palm.Table 1 is a list of materials that can be used asdisinfecting agents. Brush the tool blades clean ofdebris before placing in the disinfectant solution. Forchain saws, it is recommended that they be takenapart and both the chain and bar soaked. By havingmultiple pruning tools, one tool can be soaking in thedisinfectant solution while the other tool is used forpruning. The disinfectant solution should be replacedat least every ten trees or every two hours. Rinsetools with clean water before pruning.The following is a management suggestion. Forthe initial installation of a Canary Island date palm, itis normal to remove a large number of fronds. Usinga handsaw would be time consuming. So, either use anew chainsaw or disinfect the chainsaw between eachpalm. Thereafter, the number of leaves prunedshould be limited as only dead leaves should beremoved. This can be accomplished with a newhandsaw for each palm.While this is an extraordinary measure, it isinexpensive disease prevention management forextremely valuable palms. A mature Canary Islanddate palm that has died from Fusarium wilt isexpensive to remove and expensive to replace. It iscertainly more economical to prevent the disease thandeal with the deadly consequences, especially if thereare multiple Canary Island date palms in thelandscape (Figure 5). Using a new handsaw ordisinfecting the pruning tool is inexpensive incomparison to a devastated landscape.Figure 5. Multiple Phoenix canariensis dying fromFusarium wilt. The disease is moved from palm to palm byinfested pruning tools. Credits: H.M. DonselmanAgain, this is a disease without a cure. In anursery situation, diagnosis of this disease effectivelydestroys the crop as the plants are unsaleable andmust be destroyed. In the landscape situation, thepalm will eventually die and have to be removed. Inboth situations, but especially the nursery situation,the diseased palm(s) should be removed anddestroyed immediately. Be very careful not todistribute potentially fungal-infested soil or potting

Fusarium Wilt of Canary Island Date Palm 6mix in the nursery. Surrounding Canary Island datepalms should be monitored closely, as it is quitelikely the entire crop could be infected.The diseased palm should be incinerated orplaced in a landfill. If this is not possible (as is thecase in many Florida counties), then be sure the palmis not chipped and recycled for mulch in thelandscape. Instead, chipped material should beplaced in a compost pile. Chain saws and other toolsused for removal must be brushed free of plantmaterial and disinfected as described previously.Chlamydospores of Fusarium oxysporum f. sp.canariensis can survive for long periods in the soil,and certainly will survive in any infected root massleft behind when a diseased palm is removed.Experimental and observational evidence has shownthe potential for infecting palms, especially seedlingpalms, with this fungus via the root system.Therefore, it would not be prudent to plant a CanaryIsland date palm back into a site where Fusarium wilthad killed the previous palm(s). It is not known howfar away from the potentially fungal-infested site onemust move before it is safe to plant a Canary Islanddate palm, or other potentially susceptible Phoenixspecies.Selected ReferencesUniversity of Florida, Cooperative ExtensionService, Gainesville, FL.Simone, G. W. 2004. Fusarium wilt. Pages17-25 in: Compendium of Ornamental PalmDiseases and Disorders. M. L. Elliott, T. K.Broschat, J. Y. Uchida, and G. W. Simone, eds.American Phytopathological Society, St. Paul,MN.Simone, G. W. and G. Cashion. 1996. FusariumWilt of Canary Island Date Palms in Florida.Plant Pathology Fact Sheet PP-44. University ofFlorida, Cooperative Extension Service,Gainesville, FL.Smith, D.I., I.W. Smith and P. Clements. 2003.Fusarium Wilt of Canary Island Date Palm.Forests Fact Sheet, Department of Sustainabilityand Environment, Victoria, Australia.Summerell, B. A., H. C. Kistler, and L. V. Gunn.2001. Fusarium wilt of Phoenix canariensiscaused by Fusarium oxysporum f. sp.canariensis. Pages 263-270 in: Fusarium: PaulE. Nelson Memorial Symposium. B. A.Summerell, J. F. Leslie, D. Backhouse, W. L.Bryden, and L. W. Burgess, eds. AmericanPhytopathological Society, St. Paul, MN.Feather, T. V. 1982. Occurrence, Etiology andControl of Wilt and Dieback of Phoenixcanariensis in California. Ph.D. diss. Universityof California, Riverside, CA.Feather, T. V., D. E. Munnecke, and J. B.Carpenter. 1989. The occurrence of Fusariumoxysporum on Phoenix canariensis, a potentialdanger to date production in California. PlantDisease 73:78-80.Plyler, T. R., G. W. Simone, D. Fernandez, andH. C. Kistler. 1999. Rapid detection of theFusarium oxysporum lineage containing theCanary Island date palm wilt pathogen.Phytopathology 89:407-413.Simone, G. W. 1998. Prevention andManagement of Palm Diseases in Florida'sLandscapes. Plant Pathology Mimeo 98-4.

Fusarium Wilt of Canary Island Date Palm 7Table 1. Suggested materials and soaking times for disinfecting pruning tools.Material z % Solution Soaking timeHousehold bleach (ex: Chlorox) 25% (1 part bleach + 3 parts water) 5 minutes minimumPine oil cleaner (ex: Pine Sol) 25% (1 part cleaner + 3 parts water) 5 minutes minimumRubbing alcohol (70% isopropyl) 50% (1 part alcohol + 1 part water) 5 minutes minimumDenatured ethanol (95%) 50% (1 part alcohol + 1 part water) 5 minutes minimumzThe above materials were shown to be effective in eliminating the fungus from the wood dust or palm sap trapped onpruning tools (Simone, 1998). It is suggested that the solution be replaced after ten trees or every two hours. Rinse thetool with fresh water after soaking. Other potential disinfectants would be trisodium phosphate or quaternary ammoniumsalts. The latter is recommended at a 5% solution, soaking for 5 minutes (Smith et al., 2003).