Palm weevil appears to be spreading north


Issue Date: May 2, 2018
By Kevin Hecteman
This palm tree was killed by South American palm weevils.
Photo/Center for Invasive Species Research
South American palm weevils
Photo/Center for Invasive Species Research
A healthy Canary Island date palm. The Center for Invasive Species Research at UC Riverside maintains a webpage for reporting palm infestations at cisr.ucr.edu/palmarum_survey.html.
Photo/Center for Invasive Species Research

Is Southern California about to fall to the weevil empire? University of California entomologist Mark Hoddle is working to keep that from happening, even as the South American palm weevil continues its march northward into San Diego County and continues to worry date growers in the Coachella Valley.

"I think it's pretty widely established now in San Diego County," Hoddle said. "Obviously, the territory that's infested is now increasing. That is going to make it much harder to contain and eradicate."

Hoddle, based at the Center for Invasive Species Research at UC Riverside, said he received a "very credible report" last week of a palm tree in southernmost Orange County, about 60 miles north of San Diego, that showed all the signs of having been killed by weevils. If the report checks out, he said, it will mark a major expansion of weevil territory.

Palm weevils can fly as far as 15 miles in a day if they're so inclined, Hoddle said.

The South American palm weevil first arrived in California from Mexico seven years ago. Weevils wreak their havoc by laying eggs in the tree's crown, which generates new fronds for the tree. It's also a smorgasbord for weevil larvae.

"This is like eating ribeye," Hoddle said, pointing out that the Canary Island date palm—the trees "pruned at the top to look like a pineapple"—is by far the insect's favorite.

The larvae's voracious appetites eventually kill the crown; unable to make new fronds, the tree soon dies as well. A palm killed by weevils is distinguished by a lopsided or absent crown and a ring of sagging fronds.

The South American palm weevil represents a significant concern for California date farmers.

Albert Keck of Hadley Date Gardens in Thermal has been one of the more vocal date growers calling for increased weevil-fighting efforts, and not just on farms.

"It's not really a farm problem right now, and we don't want it to become one," said Keck, who also chairs the California Date Commission. "A lot of these invasives obviously start in the cities. What's upsetting is they eventually make their way out into the farms."

Keck said that at present, date growers have few options available.

"Right now, we're trying to sound the alarm. It's in San Diego now. We need to do something about it," he said, adding that he wished infested urban areas shared his urgency.

Hoddle has been tracking the weevil in San Diego County for nearly two years.

"We've been using drones to survey palm mortality rates through infested areas," he said, "and we've also been running surveys of urban palms in the hot zones to see how quickly palm trees are dying in that area."

Hoddle started his surveys in August 2016.

"At that time, we tagged 423 healthy palms," he said. "We survey them every six months. At the last survey in January, about 20 percent of those healthy palms have now died because of weevil attack. That's quite an alarming rate of mortality."

His strategy now involves three parts.

Fellow UC Riverside entomologist Thomas Perring is deploying approximately 100 pheromone-loaded bucket traps around the Coachella Valley, Hoddle said.

"This is basically using the traps as eyes to see whether or not there's weevil activity in the valley," he said.

The second part of the strategy involves evaluation of different types of weevil traps and baits in work intended to develop "the best trapping recommendations for the growers," Hoddle said.

Finally, he said he will work with Rainbow Tree Care Science, beginning this month, to check the effectiveness of insecticides at protecting palm trees in the San Diego County hot zone.

"We've identified palm trees that look healthy right now, and we are randomly assigning treatments to those healthy-looking palm trees," Hoddle said. "Some of those palm trees won't get treated. They'll be the control treatments. And then we're just going to see who lives and who dies over the next 12 to 18 months."

Keck said urban areas "stand to lose a terrible amount of palms," which can cost up to $10,000 per tree.

"I think the biggest constituency that stands to lose the most right now is the urban coast of California," he added. "All the landscaping that's developed utilizing palm trees is basically at risk."

Keck said there have been community meetings in San Diego, the Coachella Valley and Yuma to discuss the issue, and that date growers have supported grant applications for Hoddle's work to combat the infestation.

One such grant was received in late 2017 from the Foundation for Food and Agriculture Research, matched by UC Riverside and several companies and agricultural groups for a total of $300,000. The grant will help fund weevil-countermeasure efforts, and also helped hire a postdoctoral researcher for the project.

"But it's going to take a lot more than that," Keck said. "It's going to take a huge amount of firepower from the urban coast, from the state of California, to get involved and really get serious about doing something."

Hoddle said he sees a very symbol of Southern California at risk, noting the historic avenues in the region lined with 75- to 100-year-old Canary Island date palms that rise 40 feet or more in height.

"These are landmark trees that people expect to see when they come to Southern California," he said. "Every week that goes by, obviously the weevil's going to spread a bit further, the population's going to grow a bit larger, and those things make eradication more challenging."

(Kevin Hecteman is an assistant editor of Ag Alert. He may be reached at khecteman@cfbf.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.