Palm Insects — Palmetto Weevil

Common Palm Insect pests in north and central Florida

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The palmetto weevil can kill a large Canary Island date palm very quickly. The new fronds topple over while the lower fronds can remain green and intact for months. But the bud is dead and so is the palm.

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 palm bud, the palm tree dies.

The primary target of the palmetto weevil, an insect native to Florida, is the Canary Island date palm. Date palms, sabal palms Bismark 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.

Pineapple cut removes too much live tissue and attracts palmetto weevils to the palm. The “pineapple cut” is so named because the cut frond ends (called boots) look like a pineapple. The cut boots give off an odor that attracts palmetto weevils.

Pineapple cut removes too much live tissue and attracts palmetto weevils to the palm. The “pineapple cut” is so named because the cut frond ends (called boots) look like a pineapple. The cut boots give off an odor that attracts palmetto weevils.

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 right), 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 that hatch and chew into the center of the palm where they attack the bud, the crucial growing point of the palm. The grubs are eating palm heart like the palm hearts available in cans at the supermarket. Except in this case they are eating your palm heart.

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.

The palmetto weevil adults are large, about one inch long. (Photo by Dr. Doug Caldwell, University of Florida, Collier County Extension Service, Naples, FL)

The palmetto weevil adults are large, about one inch long. (Photo by Dr. Doug Caldwell, University of Florida, Collier County Extension Service, Naples, FL)

When the grubs have already feasted, pupated and then turned into adults searching for a mate and another susceptible palm tree, evidence of their work can always be found. Such evidence is in the form of tunnels the diameter of your thumb in the base of some of the collapsing fronds or frass pellets (photo below).

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.

I 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.

The palmetto weevil pupal stage is large, about the size of your thumb. Even if the grub cannot be found, its large tunnels can be found at the base of fronds that have collapsed. (Photo from University of Florida files)

The palmetto weevil pupal stage is large, about the size of your thumb. Even if the grub cannot be found, its large tunnels can be found at the base of fronds that have collapsed. (Photo from University of Florida files)

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. Contact your local Cooperative Extension Service office (usually found under a county government listing) for the latest pesticide recommendations for such a preventative treatment.

View of the frass pellets left near the tunnels made by the palmetto weevil grubs. (Photo from University of Florida files)

View of the frass pellets left near the tunnels made by the palmetto weevil grubs.
(Photo from University of Florida files)

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.

 

 

 

The palmetto weevil kills the bud causing the newer fronds to topple over leaving the lower fronds intact for up to several months.

The palmetto weevil kills the bud causing the newer fronds to topple over leaving the lower fronds intact for up to several months. When this happens the tree will not recover.

 

 

 

 

 

 

 

 

The infested sabal palm folds over on itself after the palmetto weevils consume the bud. This was a recent transplant and the stressed palm attracted the weevils. (Photo by Chuck Lippi)

The infested sabal palm folds over on itself after the palmetto weevils consume the bud. This was a recent transplant and the stressed palm attracted the weevils.
(Photo by Chuck Lippi)