Several of the Canary Island date palm trees that typically stand tall, full and lush along the La Jolla coastline may be falling prey to the South American palm weevil, causing them to droop, turn brown and die.
The infestation, which is throughout San Diego and is on the radar of city officials, was spotted locally by La Jolla resident William Grimm.
“I see more and more trees dying,” he said. “I live on a hillside and can look down into The Shores and it seems like every few days, there’s one. Then there’s another one. One here, one there. It’s that prolific. The infestation is pretty serious. I walk and hike and bike and have seen this happening up and down La Jolla.”
In researching what could be causing the trees to wilt, he reached out to friends in the landscape architecture field and to the UC Riverside Center for Invasive Species Research. Their opinion, he said, is that the weevil is the cause.
The city of San Diego is working with the UC Riverside Cooperative Extension to develop comprehensive management of the region’s date palms that will be affected by the insect.
In looking at photos of La Jolla trees supplied to the La Jolla Light, Mark Hoddle, biological control specialist and principal investigator at the UC Riverside department of entomology, said the trees “were killed by the weevil” and that this type of palm is “highly preferred” for the bug.
The South American palm weevil is a type of beetle native to parts of Mexico, Central and South America and the Caribbean.
Hoddle said it will colonize palm trees, attracting other weevils “by releasing an aggregation pheromone that calls in other flying weevils to the palm.”
“Once at the palm, females lay eggs, those eggs hatch into weevil grubs or larvae that feed on the palm heart,” he said. “Once the larval stage is completed, the larvae form cocoons out of palm fibers within which they pupate. After pupation is complete, the adult weevils emerge and the cycle repeats itself.”
The infestation causes drooping fronds and a collapsed or tilting crown that turns brown.
“At this stage and beyond, palms now look like giant brown umbrellas or mushrooms,” Hoddle said, and eventually the trees will die.
“Often they can’t recover because the damage is so severe,” he said. “Even if insecticides are applied, if damage is heavy, it may be irreversible; the palm can’t recover even if weevil larvae are killed off.”
He said the recent infestation is part of an “invasion” that started in 2010. “Weevils were first detected flying into San Diego in 2011, and by 2014 populations established in San Ysidro,” he said. “Weevils are very strong fliers; they can fly 15-plus miles a day if they choose to do so — at least in the lab. We don’t know if they fly such long distances in nature. Over the course of 10 years, weevils probably flew up the Baja peninsula to Tijuana, across the border into San Diego County.”
City of San Diego spokesman Anthony Santacroce said the city is aware of the South American palm weevil and is “actively removing infested palms.” Many of the trees are on city property or streets.
Santacroce said the city encourages residents to use the Get It Done app to report signs of declining palm trees in parks or along the city right of way.
Hoddle said people with susceptible trees can “undertake a prophylactic insecticide program to protect palms from weevil attack.” But, he added, “once you begin these protective insecticide programs, you are on the treill and need to keep treatments up to avoid weevil attack.”
Grimm said “it’s sad that these old trees are going to fall victim to a bug. These trees are a symbol of the SoCal and Mediterranean lifestyle. They are in Orange County and Beverly Hills; they are such a grand tree. … For me, they have been so much a part of the landscape of La Jolla. You drive under these trees and people don’t realize how much they matter until they are gone. There are whole streets in The Shores that had them planted in the 1930s and there are no other trees on the streets.”
“I think there is an emotional connection to those trees,” he added. “Certainly La Jolla would survive without them, but it wouldn’t have the same feel.” ◆
