Scientists Work to Define Threat from Palm Pest

Aria Wilcox Pest Update 24 Comments

Sunny Palms Plantation
Southern California, which in recent times ejected the red palm weevil, has a new problem to ponder. It’s the South American palm weevil, which has arrived in the San Diego area from Tijuana and likes to dine on palm trees—both the ornamental and the date-growing kind.

Insect specialists, farmers and others gathered in Bonita last week to discuss the problem.

“One of the first things date palm growers should be doing is getting informed about the situation,” said Mark Hoddle, an entomologist at the University of California, Riverside. “The second thing they could help with is just to be aware of the risks of how this weevil moves around.”

Hoddle described the weevil as a strong flier.

“But movement of live palm material, especially transplants that get moved from potentially infested areas into uninfested areas, could suddenly bring the palm weevil into close proximity to date-growing areas, where currently there are no known breeding weevil populations,” he said.

The third thing, Hoddle said, is keeping an eye out for potentially infested palm trees and bringing those to the attention of agricultural officials for investigation. The UC Riverside Center for Invasive Species Research, which Hoddle directs, has a website where people can report palm trees that may be infested, at cisr.ucr.edu/palmarum_survey.html.

Albert Keck, who runs Hadley Date Farms in Thermal and chairs the California Date Commission, attended last week’s meeting and described date growers as “very concerned.”

“We don’t want the weevil to get a foothold in the United States and then leapfrog into one of these interior valleys and come into our growing district,” Keck said. “We’re hopeful that it’s still a situation that can be contained.”

A South American palm weevil wreaks havoc by laying eggs in a growing area of the palm tree, Hoddle said; on a Canary Island palm, that would be the apical meristem in the crown, where new fronds grow.

“That’s a large, soft, juicy chunk of meat,” Hoddle said. “If you’re a weevil, it’s the most delicious part of the palm you can get into, and it’s also the most nutritious.”

Female weevils—adults are typically an inch to an inch and a quarter in length—will use their long snouts to drill holes for egg laying. The resulting larvae can grow to 2 inches long, and they feast on the crown. That kills the crown, which in turn kills the tree.

“This could be devastating to the date-growing districts of the state, and it’s just a reminder of how vulnerable we are to these invasive issues,” Keck said.

Dates represented nearly $41 million worth of crops in Riverside County alone last year, according to the county agricultural commissioner’s report.

Keck said that the response to such problems usually, and appropriately, takes an agricultural approach.

“That makes it difficult when you’re trying to reach the urban constituents and why it’s a concern to them,” he said. “Palms are extremely important to our urban, coastal California landscaping. It’s very much an urban issue right now, and we don’t want it to become an ag issue.”

Nick Condos, who directs the Division of Plant Health and Pest Prevention Services at the California Department of Food and Agriculture, talked about potential regulatory responses to the threat; besides trapping and pesticides, these could include quarantines, control methods, outreach and research.

“We have put in a farm-bill request to do a trapping program for exotic palm pests, which would include South American palm weevil,” Condos said.

Details still need to be worked out, he said, as it’s not yet known how far north or east the weevil has spread.

As for a quarantine, Condos said it’s not yet known exactly which varieties of palm are susceptible to weevil infestation. Any quarantine would likely take after a plan drawn in 2012 to combat the red palm weevil in Laguna Beach, though that plan was never activated. Quarantines can be expensive to enforce, Condos said, and can involve steps such as growing nursery stock in an enclosed structure for a year and safely transporting frond trimmings.

“Nobody was rooting for a quarantine right now,” he said. “It was just an opportunity to get all these options out there, let people start thinking about them and what we need to do, to prioritize research to pursue some of these options.”

Hoddle said drooping fronds and a tilted crown are signs a palm tree has weevils. Trouble is, by the time one sees these signs, the tree may be beyond help.

“One of the holy grails for palm weevil research is early detection,” Hoddle said. “How do you know if your palm tree’s infected before you start seeing these very obvious visual symptoms? Right now, there’s no really great early detection technology.”

As if all that isn’t enough, the weevil has a partner in crime: the red ring nematode. If this pest is in the tree, it will find its way into the weevils, which then spread it to other trees. But so far, Hoddle said, the nematode has not appeared in California.

The best chance of containing and eradicating the weevil is when the population is small and localized, he said. The most effective anti-weevil tactics involve using pheromone traps and pesticides simultaneously; traps won’t stop the infestation but will help locate affected trees.

“Then you want to apply the pesticide treatments to those infested palms,” Hoddle said. “That type of multi-pronged approach has been really effective at controlling date-infesting palm weevils in the Middle East, for example.”

Condos said CDFA will encourage palm growers to participate in weevil detection.

“Most of our successful pest responses over the past couple of years have a very large commodity presence,” he said, citing efforts to combat pests threatening citrus crops and winegrapes.

“We really wanted to make sure that (farmers) understood that this isn’t government alone,” Condos said. “They have to be part of the process.”

Permission for use is granted by the California Farm Bureau Federation when reprinting this item. Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at khecteman@cfbf.com.

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