South American palm weevil wreaking havoc on Pacific Beach palm trees
The majestic palm tree is part of San Diego’s classic iconography — symbolizing Southern California and the beach, the feel of a tropical paradise.
Most of San Diego’s palm trees are classified as Canary Island date palm trees. Unfortunately, Canary Island date palms are also a favorite snack of the South American palm weevil, a type of bug that first made its presence known in Southern California in 2011. Once a palm weevil attacks a tree, the tree begins to show visible signs of disease, such as brown, drooping fronds.
At this point, according to experts, it’s most likely too late to salvage the tree.
Palms in Pacific Beach, like the one in front of resident Carole Cruz’s house, have been infested by the palm weevil. Cruz has lived in the area for the last 13 years. She said she noticed one day that the tree outside her home was looking a bit different.
“I used to look at this palm every morning from my bedroom window,” she said. “One day, it looked a little odd. It took me a few days to realize something funny was going on — and it was that the crown was collapsing. By the fourth day, I could see many fronds turning brown.”
Cruz said she called the city on Jan. 28 to come out and remove the palm. By Feb. 13, the palm had been removed.
“The main thing about the South American palm weevil is how unbelievably fast it will take down a palm that looks perfectly healthy,” Cruz said. “The tree is virtually dead before you even know anything is going on. The crown collapsing only confirms it. So that’s what happened to the tree. I miss it.”
The weevil infestation issue is multi-faceted, said Mark Hoddle, an extension specialist in biological control in the department of Entomology at UC Riverside. The weevil has been slowly working its way up north from the Baja peninsula, where it was first discovered around the year 2000.
“It looks like San Diego County’s pretty much infested from the border all the way up to San Marcos out to probably El Cajon,” he said. “The weevil is actually spreading fairly slowly, given the fact that we’ve pretty much determined that they can fly a long way. We think the reason for its relatively slow spread throughout San Diego County is because there are just so many palm trees to feed on.
“And I suspect that the intensity of the attacks is now becoming much more apparent to people because I’m just getting overwhelmed now with email inquiries about what to do for palm trees to try and protect them from the weevil,” he added. “It’s really hitting a lot of people’s radars now.”
The weevil is about two-inches long and can fly surprisingly great lengths.
“We think they could easily fly probably 15, 20 miles in a day if they really wanted to do that,” Hoddle said.
If you’re curious, here’s how infestation works: “Adult weevils buzz around and when they find a palm tree that they like, they’ll land at the top of it, in the crown. And the adults are very good at pushing their way down between the palm fronds. They’ll try to get as close top to the trunk of the tree as possible,” Hoddle explained.
The female then drills a hole into the top of the palm with her rostrum (an elephant-like nose or beak) and lays eggs in the hole. The eggs hatch and the weevil larvae boar their way into the crown area of the palm tree.
Once the larvae hatch, they begin to feed on the palm heart, the same type of thing you could buy in a grocery store to eat.
“Weevils love eating that meristematic tissue, or the palm heart. It’s so rich and juicy and that feeding damage basically results in the death of the palm tree. It can’t grow any more new palm fronds, so the tree dies,” said Hoddle.
Dead trees look like “giant brown umbrellas” or “big brown mushrooms” because the dead fronds turn brown and hang from the top of the tree trunk.
“And that’s it, the palm is pretty much dead by that stage,” Hoddle said.
Ron Matranga , consulting arborist at Atlas Tree Service, said that it wouldn’t take many larvae to kill a palm tree.
One female can lay anywhere between 100 to 700 eggs. “And it can take as few as 30 larvae to completely damage a palm,” he said.
Recovering a palm tree that is already visibly infested is next to impossible. By the time you can see it, it’s usually too late.
“I have on rare occasions seen people treat their tree at the last minute out of extreme desperation and there must have been just a little bit of living palm material at the very top of the palm because about six to eight months later, it just started sprouting back,” Hoddle said. “I was absolutely amazed that they had saved that tree. But it had got to the point for them where it was like, we’ve got nothing to lose. We can pay $150 and treat the tree and maybe it will come back to life, if we’re lucky. If not, then well it’s going to be removed anyway.”
Controlling the infestation requires affected palms to be removed immediately, to reduce the risk of the weevils finding another host tree. Treating healthy surrounding trees with insecticide is another way to control the spread.
“The treatment is a dual-pronged treatment: there’s a crown spray, which goes directly up into the top of the palm,” said Matranga. “And then there’s a soil treatment. This chemical is put into the soil, the tree roots pull it in and is what’s called systemic, where it’s ingested into the system of the plant and moves up inside into the vascular part of the palm.”
The treatment must be repeated three to four times a year to remain effective.
“It can cost upwards of $400 to $500 per treatment for the first palm, and then sometimes only $100 to $200 per palm after that if you have multiple palms on a site,” he said. “But it does take a commitment on the palm owner’s part. You can’t just treat once and you’re good.”
Removal of a dead palm could run upwards of $1,000, Matranga said, depending on the location of the tree.
Brian Widener is the city forester for the city of San Diego. He said the city is well aware of the problem, but lack of resources limits their ability to control the spread of the infestation.
“It’s a challenging issue for us, as we’re juggling multiple issues at all times. It’s very limited on what we’re able to do at this point in time in regards to these trees. We have been removing trees as one way to keep the beetle from spreading from tree to tree,” Widener said.
Tree removals are also important for public safety. Once the tree is infected, the dead fronds fall off and can be a safety issue, he said. But it’s also possible that the top of the tree could fall off.
“We always encourage people to call or use the Get It Done app as soon as possible and report the problem,” Widener said.
Right now, the city is closely monitoring the issue, while also treating some palms with insecticide. The palms currently being treated by the city are part of a pilot program to test the effectiveness of such treatments.
“With these kind of issues, monitoring the situation is always one of the key components,” Widener said.
So far, the city has treated palm trees with insecticide in two areas: the trees lining Catalina Boulevard in Point Loma and other affected trees in University Heights.
Hoddle said that managing the infestation is possible. He has worked on studies with similar bugs in the Middle East. In Saudi Arabia, where palm trees flourish due to the intense heat, the infestation of the red palm weevil, which is a close relative to the South American date palm weevil, has been contained through a combination of insecticides, dead tree removal and using pheromone traps to lure the weevils into buckets where they are captured and killed.
“There is a pheromone for the South American palm weevil and it’s very good at drawing the weevils into traps. We can catch lots and lots of them. But the problem is right now is there’s no systematic trapping plan for South American palm weevils in San Diego County,” Hoddle said. “It would require a big input of money, either from the state or the federal government through the USDA, to lay out a big response to this weevil through using these traps. And the work on other weevils and the South American palm weevil suggests that you can trap it down to very low numbers if you’re willing to put the resources into financing that.”
As far as the city is concerned, Widener said it’s important to keep dialogue open with local politicians about options and treatment plans.
“Date palms, in particular Canary Island date palms, can have a lot of maintenance work over the years,” he explained. “Even though we all appreciate them as being a very iconic type of palm in our city, it’s a balancing act on how we keep some of them, at least if we’re going to do future treatments, and which ones we have to let go.”
For now, Widener said concerned citizens can either reach out to a tree care company, if the tree is on private property, or notify the city through its Get It Done app, if the tree is on public property.