Petiole (Rachis) Blight of Palm - Manatee County Extension Office ...

Petiole (Rachis) Blight of Palm 4office or FEPDC for information on samplesubmission and cost of laboratory diagnosis. Ingeneral, the entire leaf should be placed in acardboard box or tube and padded with dry paper.The leaf can be cut into pieces with a handsaw foreasier packaging. Do not place the pieces in a plasticbag.Disease ManagementVery little is known about petiole blight,including the specific environmental conditions thatencourage disease development. It is presumed thathigh humidity is required for fungal infection anddisease development, as that is a requirement formany plant diseases that affect above-ground tissue.It is also presumed that spores are the primary meansof fungal movement from palm to palm. Based onthese assumptions, sanitation and water managementare the basis for petiole blight management.Removal and destruction of severely infectedleaf fronds would be suggested as a means ofreducing inoculum (available spores to infect otherleaves and palms). This would be especially criticalin a nursery situation where palms are planted closertogether and are more numerous. However, if thepalms are in the landscape and under nutrient stress,pruning should be minimal as removal of too manyleaves may be detrimental to the palm rather thanbeneficial.In a nursery, increasing distance between plants,increasing air movement, and irrigating in the earlymorning hours to reduce leaf wetness at night arecritical water management components. Whenpossible, overhead irrigation should be eliminated.fungicide sprays to protect the petiole and rachis maybe useful. For palms where the canopy is no longeraccessible, broad-spectrum systemic fungicide soildrenches may be useful, although information as tomovement of systemic fungicides in palms isextremely limited.It is critical to understand that fungicides do notcure the damage already present on the palm. Planttissue does not “heal” itself. Once the damageoccurs, it will remain for the duration of the life ofthat particular leaf. Fungicides are used to preventfurther spread of the disease by protecting a leafpetiole and rachis that has not yet been infected by thefungal pathogen.Selected ReferencesBarr, M. E., H. D. Ohr, and M. K. Murphy.1989. The genus Serenomyces on palms.Mycologia 81:47-51.Hyde, K. D., and P. F. Cannon. 1999. Fungicausing tar spots on palms. Mycologial Papers,No. 175. CABI Publishing, Wallingford, U.K.Simone, G. W. 2004. Rachis blight. Pages33-34 in: Compendium of Diseases andDisorders of Ornamental Palms. M. L. Elliott, T.K. Broschat, J. Y. Uchida, and G. W. Simone,eds. American Phytopathological Society, St.Paul, MN.Simone, G. W. 1998. Prevention andmanagement of palm diseases in Floridaslandscapes. PP-Mimeo 98-4. FloridaCooperative Extension Service, Gainesville, FL.Since no fungicides have been evaluated forefficacy in managing petiole blight, fungiciderecommendations are educated guesses at best.Fungicides would only be recommended in thosesituations where a palm is being seriously affected, orthe potential for an epidemic is high, such as in anursery. Never initiate a fungicide program withoutfirst initiating a cultural control program as describedabove.For palms where the canopy is still accessible forspraying, broad-spectrum contact or systemic foliar