FROM THE GROUND UP

Weevil woes

Destructive beetle killing region’s Canary Island date palms

By NANCY NYGARD

The palm tree is an iconic silhouette in San Diego County. Though not native to our region, palms have become a symbol of Southern California, adding a tropical feel to our decidedly nontropical Mediterranean climate.

The Canary Island date palm (Phoenix canariensis) has a strong presence in Coronado and throughout San Diego County, especially in the yards of older homes.

Once considered virtually impervious to pests, this stout-trunked palm has a new enemy: the South American palm weevil (Rhynchophorus palmarum), also known as SAPW. This voracious insect was first discovered ravaging palms in the Tijuana area in 2010. Since then, the South American palm weevil has been eating its way north, creating a “palmageddon,” killing thousands of San Diego County palms in its ever-growing path.

The South American palm weevil is a large black beetle, approximately 1.5 inches in length, with a large, distinctive snout. Female weevils use the snout to bore into the base of fronds and lay their eggs inside the tubular holes. When the eggs hatch, the larvae gnaw their way into the heart of the palm, then spin a protective cocoon made from palm fiber. These destructive actions cause the palm heart to rot. If not promptly treated, the tree will eventually die.

After the larvae morph into adult weevils, they fly from the host tree in search of a new palm to begin the infestation cycle again.

“Up to 233 larvae have been documented inside collapsing Canary Island date palms, with an estimated average of 24 weevil larvae being capable of killing a Canary Island date palm,” said Dr. Mark Hoddle, director of the Center for Invasive Species Research at the University of California Riverside. Those findings were researched in Florida on Rhynchophorus cruentatus, a related palm weevil. “It may be reasonable to think that these data may be somewhat applicable to SAPW attacks on Canary

The South American palm weevil measures approximately 1.5 inches in length. Female weevils use their large snout to bore into the base of fronds and lay eggs inside the tubular holes.

CENTER FOR INVASIVE SPECIES RESEARCH, UNIVERSITY OF CALIFORNIA RIVERSIDE

Island date palms in California.”

It’s easy to spot SAPW casualties. Dead palms with brown fronds droop from flattened crowns. According to the University of California Cooperative Extension San Diego, these are the signs of palm weevil infestation: » Yellowing of the foliage. » Flattening of the crown. » Holes and tunnels near the base of fronds. » Pupal cases on the ground near the palm.

Victims of the weevil can be seen in many areas of Balboa Park and along Barnett Avenue at the Marine Corps Recruit Depot San Diego. Here in Coronado, the first identified SAPW casualty is the Canary Island palm in the 100 block of Orange Avenue near the Coronado Veterinary Hospital. Others have been discovered. The city of Coronado’s Public Services department is actively treating the palms.

How can you prevent a “palmageddon” on your property? Currently, the best option is preemptive twice yearly spraying of the fronds and crown with a contact insecticide. But if, despite your best efforts, SAPWs find their way to your palm, Hoddle recommends treating it with a systemic pesticide, which can be injected or applied to the truck or injected into the surrounding soil. Another option is applying a contact insecticide to the foliage. Consult with a trusted tree service for the best treatment for your palm.

If a palm tree cannot be saved, Hoddle advises removal by a professional arborist. To prevent further spread of these destructive insects, the fronds and remains of the heart should be chipped

LESLIE CRAWFORD The Canary Island date palm in the 100 block of Orange Avenue is the first identified South American palm weevil victim in Coronado.

on site to kill the larvae, pupae and adult weevils. The rest of the tree should then be wrapped in a tarp and transported immediately to a landfill. Palm tree removal can be expensive, but leaving a palm killed by a weevil is dangerous — the heavy, rotted palm crown could topple and severely injure someone or damage property.

Even if you don’t have a Canary Island palm, don’t let your guard down. These ravenous bugs have broadened their palate. Though the weevils originally only attacked the area’s Canary Island palm population, other palm varieties including Bismarckia, Mexican fan palms (Washingtonia robusta), Chilean wine palms (Jubaea chilensis) and Bermuda palmettos (Sabal bermudana) have been targeted by the hungry weevil.

The UC Riverside Center for Invasive Species Research is requesting the public’s help in tracking the South American palm weevil in San Diego County. To report palms which may be infested with SAPW, complete the online form at cisr.ucr.edu/ invasive-species/palmarum-survey. ■

Nancy Nygard is a UCCE Master Gardener.