South American Palm Weevil: What Date Palm Owners in Southern California Should Know

The South American palm weevil is the pest date growers in California watch most closely right now. It has already killed palms by the thousands around San Diego, and adult weevils have been trapped in the Coachella Valley, the heart of American date country. Here is what’s known, what to look for, and what we do about it in our own grove.

What it is and where it’s been found

The South American palm weevil (Rhynchophorus palmarum) is a large black weevil native to Mexico, Central and South America. According to UC Agriculture and Natural Resources:

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• It was first detected in San Diego County in 2011, with breeding populations confirmed in 2015.
• Industry experts estimate it has killed more than 20,000 palms in the region.
• Its strongly preferred host is the Canary Island date palm, but it also attacks other palms, including the edible date palm.
• CDFA has trapped adult weevils in the Coachella Valley, roughly 120 miles from San Diego. An infestation there has not been confirmed.
• Adults are strong fliers; in UC Riverside tests some flew non-stop for up to five hours.

How it kills a palm

Females lay eggs in the crown. The larvae tunnel into the growing heart at the top of the palm and feed on it. Because a palm has only one growing point, once that is destroyed the palm dies, sometimes within months. Badly damaged crowns can break off and fall, which makes infested palms a safety hazard as well as a loss.

Signs to watch for

• The crown starts to tilt, droop or collapse to one side.
• Center fronds wilt, yellow or die while older fronds still look normal.
• Fronds drop suddenly or the crown looks “flattened.”
• In advanced cases the whole top of the palm breaks away.

If you see these signs in Southern California, report the palm through UC Riverside’s South American palm weevil survey, and get a tree care company or arborist to confirm it.

What UC researchers recommend

UC Cooperative Extension’s guidance for protecting palms, in brief:

1. Prune only from December through March, when weevil flight activity is low. Fresh cuts attract them.
2. Trap. Traps baited with fermenting dates, yeast and water plus a commercial pheromone lure both monitor weevils and reduce their numbers. UC advises placing them well away from the palms you’re protecting, in shade.
3. For valuable palms, insecticide is the most reliable protection, usually systemic treatments applied by a professional. UC is clear that this is an ongoing commitment, not a one-time treatment.
4. Act early. Once the growing heart is badly damaged, the palm usually can’t be saved, and dead palms should be removed promptly so they don’t become breeding sites.

What we do in our grove

We don’t spray our palms or fruit, so our defense is mostly attention and timing. Our grove sits on its own at the end of the road in Sky Valley, with no neighboring farms. We prune only in the December–March window, walk the rows looking at crowns, and keep dead material cleared out. If the weevil does establish in the valley, every grower here will have to rethink, and we’ll write about what we decide.

If you’re planting, it is one more reason to source offshoots locally from groves you can see, rather than moving palm material from areas where the weevil is established.

Quick Answers

Is the South American palm weevil in the Coachella Valley? Adults have been trapped there, but as of UC’s reporting an infestation has not been confirmed.

Can a palm with palm weevil be saved? Sometimes, if treated aggressively early. Once the growing point is destroyed, no.

Does it attack date palms? Yes. Canary Island date palms are its favorite, but edible date palms are susceptible.

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