Wanted: the red palm weevil, tree killer

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The red palm weevil, an insect widely considered to be the biggest threat to palm trees worldwide, has been discovered in Laguna Beach — the first time the Southeast Asian pest has been detected in the United States.

The discovery was made in August, when a tree trimmer removed a dying Canary Island date palm from a home garden. He sent an insect and debris from the damaged tree to the California Department of Food and Agriculture, which confirmed the identity of the pest as the red palm weevil and forwarded the samples to the U.S. Department of Agriculture. Investigators’ subsequent review of the site turned up another red palm weevil on a different property, about 500 yards away. Pheromone traps were set in the area, and state and federal officials are continuing detection efforts. No other red palm weevils have yet been found.

The red palm weevil — about 1.5 inches long with a long snout and sometimes a red stripe down its back — is a reluctant but strong flyer. When it searches for a new home, it can travel about half a mile at a time. It targets many varieties of palm trees including Phoenix and Queen palms; other types such as the European fan palm and Washingtonia filifera, a Southern California native that’s also called the California fan palm or desert fan palm, have shown resistance to infestation.

The weevil has caused major damage in the Arabian Gulf, around the Mediterranean and across Asia, including Japan, Vietnam, Pakistan and the Philippines. In Indonesia, the pest has hit palm oil plantations.

An infected tree will die back from the crown, according to Nick Nisson, an entomologist with the California Department of Food and Agriculture. The weevil lays eggs in the crown, where the larvae have a steady supply of young, tender leaves on which to feed. Emerging fronds appear bent or twisted, or they turn a dull green before dying. Other potential signs of an infestation: tunnels on the trunk; palm fronds oozing with a viscous, smelly fermented liquid; coarse frass, the excreta produced when the larvae chew up the tree from within (it looks like ground-up tree mixed with three-quarter-inch palm fibers); or an audible sound of chewing.

Red palm weevils typically take a year or two to kill a tree. Symptoms differ from those of a fungus common among Phoenix palms in Southern California. The fungus kills older fronds but leaves younger leaves appearing healthy.

Palms from other countries are prohibited from entering the U.S., so officials don’t know the origin of the Laguna Beach weevils. Officials found no new landscaping in the area where the bug was found.

Treatments vary, but Nisson said there is no consensus on the best solution. Insecticides, traps and biological controls have all been used elsewhere, with limited success and conflicting reports about their efficacy. A healthy tree and early detection are essential to surviving an infestation.

To report palm trees whose problems sound consistent with a red palm weevil infestation, call the California Department of Food and Agriculture pest hotline, (800) 491-1899, or report online. UC Riverside’s Center for Invasive Species Research has more photos of the pest.

-- Jeff Spurrier

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