Post by Bob Mertens; Horticulture Program Specialist
Once considered a minor pest of palms, the palmetto weevil (Rhynchophorus cruentatus) has in recent years become a serious problem on Canary Island Date palms (Phoenix canariensis) and increasingly on Bismarck palms (Bismarckia nobilis) and Washington palms (Washingtonia robusta). Often attacking stressed or over-trimmed palms, the initial damage, death of the spear leaf and surrounding new growth, usually goes unnoticed until it is too late for effective pesticide treatment.
The largest weevil in North America and a Florida native, the palmetto weevil is found from coastal South Carolina to southern Texas and until recently was the only species of palm weevil in the continental U.S. Weevils are a family of beetle that has the mandible at the tip of a snout-like projection. While the adults do feed, it is the larvae that do the most damage to palms.
Attracted to stressed and over-trimmed palms, the weevil lays its eggs in leaf bases and pruning wounds. Eggs hatch in three days. The larvae are grubs which begin boring into the trunk heading for the bud or apical meristem of the palm. Once the bud has been destroyed, the palm is dead, even though green leaves may persist for some time. The palm’s canopy often collapses and may fall over, a condition called “Popped neck.” If the palm is dissected at this point, larvae, cocoons, and adults may be found in the area of the crown.
Healthy, vigorous palms that have not been over-trimmed or suffered other stresses are usually not attacked by the palmetto weevil. Remove only brown leaves and follow proper fertilization recommendations by the UF/IFAS Extension. Older palms, weak, stressed palms, and palms that have been over-pruned are much more susceptible to an infestation. Once infested, there is little if any chance of saving them, even if the problem is detected early. It is therefore important to remove infested palms immediately to prevent the spread of weevils to adjacent palms. It is possible to apply pesticides prophylactically to adjacent palms to prevent further infestation but this must be done on a regular, continuing basis.
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For more information on the palmetto weevil, please see the UF/IFAS publication at the link below.