RSF Association board approves new palm weevil research study in Rancho Santa Fe

The flatted top of a palm weevil-infested palm on the golf course.
(Caitlin Kreutz)

On Feb. 2, the Rancho Santa Fe Association board approved the Covenant’s participation in a new UC Riverside research study that will help target the South American Palm Weevil, a destructive pest that has plagued palm trees throughout San Diego County.

With a $1 million grant from the California Department of Pesticide Regulations, Dr. Mark Hoddle will experiment with a more environmentally-friendly, less expensive method for reducing weevil populations than the current method of insecticide applications to palm foliage and soil.

“We are excited about the new opportunity to potentially help control this,” said Caitlin Kreutz, the Association’s environmental resource coordinator.

While the palm weevils prefer to feast on Canary Island date palms, they’ve also been found to lay eggs and kill a variety of Southern California palms—the pest has killed an estimated 20,000 ornamental and date palm trees in the county. There are about 16,000 Canary Island palms in the Ranch and high mortality rates are starting to have an impact in the community: “These flat top palms are everywhere,” Kruetz said.

Once the weevils get into a palm tree, they lay eggs which hatch into really large larvae which destroy the palm’s heart. The first sign of infestation is seeing the crown of the tree droop and turn brown. The tree can’t grow any new fronds and all that is left is a halo of dying fronds in a mushroom shape, like a brown umbrella.

While they have value as an ornamental tree, the Canary Island palms are an invasive species that sap resources away from native vegetation and displace habitat for native species. As the palms are also highly flammable, Kreutz said they are a part of the Association’s invasive species removal and fuel reduction initiatives.

Currently the best way to protect the trees is an application of insecticide at the crown or using a systemic insecticide to drench the soil beneath the tree. The applications have to be made frequently and it can become very expensive.

Hoddle, a biological control specialist and principal investigator at the Center for Invasive Species Research at UC Riverside and leading palm weevil researcher will experiment with his new “Attract and Kill” method in Rancho Santa Fe, using the weevil’s biology against itself rather than spraying an entire tree with insecticide.

With the method, a dollop of low-concentrated insecticide is mixed with an irresistible weevil pheromone and placed in a hanging trap.

Traps will be hung 1.5 meters above the ground in four plots throughout the Covenant with different concentrations in each plot. There will be 1,250 traps in total, all on Association-managed properties, roadsides and trails: “We are not asking to access any private properties,” Kreutz said.

The traps will be checked every two months and it’s possible that the study will expand into the neighboring communities of Fairbanks Ranch and Encinitas.

With the Association’s FireWatch program, they are uniquely set up to track the study’s progress—Kreutz said they plan to use FireWatch maps to measure efficiency and count palm loss over the next two years of the study.