Palmetto Weevils Killing Palms

Palmetto Weevils Killing Palms

Calls about Canary Island date palms infested with weevils have been coming into the office, and a Canary Island date palm at the Florida Botanical Gardens was found to be infested with palmetto weevil, Rhynchophorus cruentatus Fabricius.

The adults vary in color from solid black to almost completely red with a variable black pattern. They are about ¾ to 1 ¼ inches long. The larvae, or grubs, are legless and creamy to yellowish in color. Their head is dark brown and very hard. Mature grubs can weigh up to 6 grams.

Male weevils are attracted by the odors “palm esters” given off from dying, wounded, or recently transplanted palms. As soon as a male weevil finds a palm like this it settles in and starts releasing an aggregation pheromone “cruentol” to attract other male and female weevils. The two odors together are very attractive to weevils and they come flying in just like people flocking to the mall during a great sale. As more males land on the host, they also start releasing curentol to attract more males and females. Once a population has gathered on the tree they start mating and soon eggs are laid.

Symptoms of a weevil infestation vary, but generally an irreversible decline of younger leaves begins. In palm species with upright leaves, such as the Canary Island date palm, the older leaves begin to droop and quickly collapse. As the eggs hatch and the larvae start to feed on the crown of the palm the damage and associated rot becomes so severe that the top of the palm falls over. If the crown is examined at this point larvae, cocoons and adults will be found in the crown region. Early detection of weevil infestation is difficult and even during the early stages of an infestation treatment may be too late to save the palm.

Treatment: The best response is to cut down the infested palm and destroy it before new adults can emerge. Applying insecticides to infested palms is futile. Newly transplanted palms can be treated with insecticides, but the costs can quickly become too expensive unless only a few trees are protected.

Host palms include: Our native cabbage palmetto (Sabal palmetto) and saw palmetto (Serrenoa repens). Several exotic species which have been infested include: Canary Island date palm (Phoenix canariensis), date palm (Phoenix dactylifera), Pritchardia species, Washingtonia species, royal palms (Roystonea sp.), Latania species, coconut palm (Cocos nucifera) and Caryota species.

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Posted: July 11, 2011

Category: Pests & Disease
Tags: Weevils

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