Study of palm-killing weevils in Rancho Santa Fe yields promising results

The monitoring traps in Rancho Santa Fe have trapped hundreds of palm weevils.

BY KAREN BILLING,news%20for%20Rancho%20Santa%20Fe.%E2%80%9D

DEC. 13, 2023 6:44 AM PT

Earlier this year the Rancho Santa Fe Association and Fairbanks Ranch partnered with UC Riverside on a new research study targeting the South American Palm Weevil, the destructive pest that has killed thousands of ornamental and date palm trees in the county. Once the weevils get into the trees, they destroy the palm’s heart, leaving the crown of the tree a halo of brown dying fronds in a mushroom shape.

With a $1 million grant from the California Department of Pesticide Regulations the homeowners associations are testing a more environmentally-friendly and less expensive method for reducing the weevil populations than the current method of insecticide applications to palm foliage and soil.

While the project was approved in February, the first traps weren’t set until the fall. According to the RSF Association, the Picusan monitoring traps have been set in the public right of way, hidden by vegetation. Inside the trap, a mixture of water and dates ferment, attracts the adult weevils inside where they get stuck and cannot crawl out again.

In the latest count from their trap monitoring survey on Nov. 30, they caught an impressive 796 weevils, including 230 males and 566 females.

“Last month we caught around 700, so there were around 100 more this go round, which is interesting since weevil numbers usually decline in the colder months,” said Caitlin Kreutz, the Association’s environmental resource coordinator.

In late March 2024, UC Riverside will start the next phase of the study which involves placing ‘“Attract & Kill” hanging pheromone traps. The traps will be hung in trees and other vegetation in the roadside right-of-way and along trails, out of view and out of the way of any human or pet activity.

“Early findings from a sister study for the Red Palm Weevil in Egypt is showing an impressive reduction in weevil counts with the deployment of the hanging pheromone traps,” Kreutz said. “This is very promising news for Rancho Santa Fe.”

Palm mortality will be tracked over the course of the two-year study using FireWatch mapping and AI analysis of palm deaths and removals.

A more detailed update on the study is expected to be provided at a future board meeting.

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