Beautiful Bismarck Palms Victims of the Palmetto Weevil

Bismarck palms (Bismarckia nobilis), native to the island of Madagascar, near the east coast of Africa, is a very popular landscape palm in Southwest Florida.

When we first bought our house in Marco, the pair of Bismarck palms on each side of the driveway were beautiful and helped our decision to purchase the property. The Bismarck palm’s huge crown, stout trunk and stunning silvery, blue-green foliage made an impact to the front landscape.

Sadly, we lost both Bismarck palms to the infestation of the evil palmetto weevil. It happened very suddenly. After a week of rain, we noticed a couple of fronds were drooping followed by the collapse of the top crown. Initially, we thought it was rot.

We had it removed immediately and the landscapers found larval grubs that bore into the top trunk at the softer heart of the palm. According to Stephen Brown of the University of Florida, IFAS, Lee County Extension, the number one cause of the demise of Bismarck palms in Southwest Florida is the palmetto weevil.

After a conversation with Tom Becker of the University of Florida/IFAS, Collier County Extension, he indicated that Bismarck palms are often beyond the stage of saving by the time any damage is apparent on the trunk or leaf fronds. Dying and wilting of younger leaves is the first sign as the weevils work in the tree’s soft interior; then the whole crown weakens and drops off called “popped neck” condition.

Palmetto weevil (Rhynchophorus cruentatus Fabricius) is native to Florida and the Southeastern United States. The adult weevils can vary in coloration from nearly solid black to almost solid red with variable black pattern. It also varies in size from 1.9 to three centimeters and is the largest weevil in North America.

According to Brown, the adult insects are attracted to stressed and weakened palms. Palmetto weevil adults are active flyers and can be found throughout the year but particularly during the summer and fall months. When not flying in search of a host palm, they hide between the leaf bases and stems of healthy palms.

The most common palms in Florida that are susceptible include: Canary Island Date Palm, Bismarck palm, Royal palms, and Coconut palms. According to the University of Florida/IFAS website, Palmetto weevils attack palms that are recently transplanted as well as palms that are over-pruned, wounded, stressed or nutrient deficient.

Stressed palms release a volatile odor called “palm esters”. Palm weevils are able to detect these odors and are attracted to these trees. Once the palm weevil finds such a host, it will then release hormones that attract more palmetto weevils and when a population of weevils gather at a tree, mating and egg laying take place.

The larva will bore into the heart of the palm and eat their way through the crown or heart of the palm. As the larvae grow and feed, they create cocoons from which the adult weevil emerges.

This tunneling introduces water into the top/crown and rot begins as a secondary issue Immediate removal of the infected palm is highly recommended to prevent weevils spreading to other palms in the neighborhood.

Healthy palms are less likely to be infested. Palm weevils are pests to exotic palms from other parts of the world but have been known to attack some native palms.

Native Host Plants:

Sabal palms

Saw palmetto

Florida thatch palm

Royal palms

Paurotis palms

Cabbage Palms

Other Host Plants:

Canary Island date palms

Bismarck palms

Fan palms

Date palms

Coconut palms

Latania palms

Fishtail palms

Tom Becker of UF/IFAS, Collier County recommended planting less exotic and more native palm species to avoid the environmental conditions that stress palms such as extreme heat, too dry, too wet, etc.

Brown also added that prevention treatment at the late stage rarely prevents death of the palm. There are systemic pesticides that are applied as injections or as a soil drench or trunk sprays by professionals, but these are often used with newly transplanted susceptible palms.  

As of this writing, one mature Fox Tail palm was showing signs of palm weevil infestation and it also was removed.