Palmetto Weevil - Native Florida Palm Pest
Palmetto weevil (Rhynchophorus cruentatus) damage quickly becomes evident as the upper fronds of the attacked palm collapse often giving the impression that the top has fallen out of the palm tree. The lower fronds can remain green for months. But without the central palm bud, the palm tree dies.
The primary targets of the palmetto weevil, an insect native to Florida, are the exotic Canary Island date palm and Bismarck palm. Date palms, sabal palms, and Washingtonian palms are also susceptible to a much lesser extent to attack by the palmetto weevil. The list of suceptible palms is a little longer for south Florida. When a Canary Island date palm is pruned in the “pineapple cut,” the palm releases an odor which is irresitible to the palmetto weevil. If you have your Canary Island date palm pruned in the “pineapple cut,” you are really putting out the welcome sign for the weevil. Instead only dead fronds should be removed from Canary Island date palms. When a live frond is cut, the irresistible odor is released.
In addition to the Canary Island date palm, which is the primary target of the palmetto weevil, secondary targets are stressed palm trees from the susceptible list of palms above. This means recent palm transplants undergoing transplant stress are targets for the palmetto weevil. The adult weevils (photo left), sensing the stressed palm, congregate at the base of the fronds to mate. The female weevil then deposits eggs at the base of the fronds. When the eggs hatch, the grubs hatch and chew into the center of the palm where they attack the bud, the crucial growing point of the palm. The grubs then begin to eat the growth bud of your expensive ornamental palm.
The immature grub stage is the culprit that kills the palm. The grub is large, about the size of your thumb, and can do extensive damage to the palm heart or bud. Often there are many grubs infesting the bud assuring a quick death for the affected palm. Then slowly the top starts to bend over and some of the fronds collapse. If diagnosed early in the collapse of the upper fronds, we can sometimes find some grubs still at work. It makes quite an impression when one of these huge grubs is plucked out of the crown and dropped at the feet of the homeowner.
Once the palmetto weevil damage becomes visible, there is no hope of recovery even with a subsequent treatment of a strong insecticide drenched into the crown. The damage has been done.
We do not normally like to recommend preventative treatments for most insect problems in the landscape. However, a preventative treatment can be appropriate to protect a high value palm such as the Canary Island date palm from the palmetto weevil. Until recently a twice-a-year prophylactic treatment of an appropriate insecticidal crown drench has been recommended for Canary Island date palms.
Recently at a University of Florida Palm Maintenance Conference in Ft. Lauderdale, entomologists described a much more aggressive regimine of monthly treatments with imidacloprid soil drenches and surface spray on the cut ends of the boots which is the main attractant for the weevils. The imidacloprid is systemic and is quickly taken up into the Canary Island date palm and moved upward through the trunk and the crown to the fronds. However, the important area to be protected is the upper part of the trunk (the “pineapple”). The imidacloprid does not remain for long in the upper trunk but instead continues to move upward and outward to the frond ends where it is not needed. Consequently, monthly soil drenches are needed between March and November to keep an adequate level of imidacloprid in the upper trunk.
Unfortunately, these preventative treatments are not always effective in preventing an infestation and can cause extensive residual death to any insect that comes in contact with the treated palm, including beneficial insects like bees and butterflies. Contact your local Cooperative Extension Service office (usually found under a county government listing) for the latest pesticide recommendations for such a preventative treatment.
Often the lower fronds can remain green for several months following the death of the bud giving some hopeful homeowners the illusion that the palm will recover. It won’t. Leaving the palm in place instead of grinding it up for mulch will allow hundreds more palmetto weevils to infest the trunk and use it for a breeding ground and nursery. Cut the palm down and grind it up.