Stephen H. Brown, Horticulture Agent Lee County Extension, Fort Myers, Florida (239) 533-7513 firstname.lastname@example.org http://lee.ifas.ufl.edu/hort/GardenHome.shtml Lightning Strikes on Coconut and Royal Palms South Florida has been designated by some as the lightning capital of the world. Given so many strikes, the probability of damage to plants is very high. Coconut (Cocos nucifera) and royal palms (Roystonea regia) are particularly susceptible due to their great height, but other tall palms are equally susceptible. Lightning season in South Florida is generally from mid-June through September. Heat and Speed of Lightning The most important effect is the extreme heat, speed and shock waves generated by the bolt. The electrical current produces temperatures in excess of 50,000°F in a millionth of a second. The velocity is about 1/10 the speed of light making the trip from cloud to ground, through or around the plant and back to the cloud in about 100 millionths of a second. A direct lightning strike on a palm is usually fatal. Indications that Lightning has Struck a Palm Diagnosing a lightning strike is very important as the symptoms may be confused with other causes such as Thielaviopsis trunk rot. Lightning injury symptoms are variable and could include the following: • • • • • • • • • • • • • Symptom onset occurs within days of recent thunderstorm. A sudden collapse of the crown occurs, usually beginning with the older, lower fronds. The collapsed fronds are at first green but become brown and necrotic within days or in two to three weeks. The crown shaft of royal palms is sometimes broken and collapsed at its base. An upper hollowed trunk sometimes occurs in royal palms. The hollowed trunk may at first be filled with slush from the overheated shattered tissue. Odorless wound during the first few days of the injury and perhaps weeks thereafter. Longitudinal gash on the trunk and/or crownshaft. Shot holes in the trunk. Bleeding of the trunk. Fallen nuts. Injury to understory plants. Several palms can be killed by a single strike if they are in close proximity. The lightning can ricochet from one palm to the other in a grouping. If this occurs, it is possible that palms directly hit will die very quickly, whereas the other palms are more likely to linger for months before dying. Management Lightning injuries are usually fatal to palms although some may survive six months or longer following a strike. The injury cannot be treated, and prevention by mounting lightning grounds within palm canopies is impractical for all but the most valuable palms. Dead trees and palms are a scarce resource in many urban sites. A dead palm can remain standing for years without any fronds. If it is not a danger to pedestrians or structures, it could conceivably serve as a “snag” to attract wildlife. It is an ideal nest site for woodpeckers and other cavity-nesting birds that cannot excavate their own nesting cavities. However, dead palms also serve as a magnets for Ganoderma Butt rot to become established in the landscape and that is a good reason not to keep them around. If the palm is removed, the stump should be ground-up to prevent it from becoming a food source for Ganoderma zonatum, the fungus that causes Ganoderma Butt rot. Coconut Palms Struck by Lighting Three coconut palms affected by lighting strike. The effect is less pronounced from first to last palm. August 7th. July 20th August 8th Continuing decline of the palms. September 3rd. August 8th Coconut Palms Struck by Lightning Late July Early September Collapsed fronds and fallen nuts. Early October Late July Decline of a Royal Palm Struck by Lightning August 10 September 1 August 22 September 1 Decline of a Royal Palm Struck by Lightning September 25th Longitudinal gash on trunk. September 25th October 6th The damaged spear leaf is the last to topple. October 6th October 20th The necrotic crown and crownshaft will soon fall. October 20th Symptoms of a Royal Palm on September 23rd struck by Lightning Two Days Before Lighting struck palm with broken crownshaft is being removed from the landscape. Fresh mush is pulled from the odorless trunk. The damage has caused a large cavity in the upper portion of the trunk. The damage extends to the lower trunk but with no apparent cavity. Additional Indications of Palms Struck by Lightning Collapsing crown of coconut palm. Scorched understory hibiscus plant by struck queen palm. Bleeding from a coconut trunk. References Broschat, T.K. 2011. Physiological Disorder of Landscape Palms. University of Florida Research and Education Center, Fort Lauderdale, Florida Nelson, S.C. 2008. Lightning Injury to Plants. University of Hawaii Cooperative Extension Service, Manoa, Hawaii Zona, S. 2008. When Lightning Strikes. Growing Palms: Horticultural and Practical Advice for the Enthusiast. Palm Journal, International Palm Society Palm Links Bismarck Palm Buccaneer Palm Cabbage Palm Cabbage Palm Pictorial Cold Damage of Coconut Palms Cold Damage of Christmas Palms Diseases of Palms Florida Native Palms Power Point Florida Thatch Palm Fusarium Wilt of Queen Palms Fusarium en Palma Reina Ganoderma Butt Rot Video Ganoderma Butt Rot Development Video Hurricane Palm Recovery Identification of Palms Nutrition and Fertilization of Palms Palm Aphids Power Point Palm Bagworms Palmetto Weevils Attack Bismarck Video Palmetto Weevils Attack Canary Island Video Palmetto Weevil Grubs Video Portrait Gallery Pruning a Cabbage Palm Video Root Initials Some Palm Problems Power Point Transplanting Sabal Palms All but one pictures taken by Stephen H. Brown. This fact sheet was reviewed by Drs. Tim Broschat and Monica Elliott, Fort Lauderdale REC; Peggy Cruz, Lee County Extension and Connie Brennan, Lee County Master Gardener. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, religion, age, disability, sex, sexual orientation, martial status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. 9/2014.