There is a new threat to Southern California Palms, it’s called The South American Palm Weevil (SAPW).
These are destructive beetles well known for attacking Palms in their native habitats of Mexico, Central and South America.
In December of 2010 reports of dying Canary Island palms in Tijuana, Mexico showed symptoms of palm weevil feeding. After physical examination of the declined palm it was found to be infested with Rhynchophorus palmarum a.k.a South American Palm Weevil (SAPW).
In 2011, the SAPW was first detected in the San Diego county, near the Tijuana border area of San Ysidro, California.
Since then, trapping and monitoring have found nearly 100+ adult weevils and approximately 50 verified cases of dead Canary Island date palms in Southern San Diego border areas of San Ysidro, Chula Vista, Sweetwater Regional Park, El Cajon and Balboa Park area due to the SAPW. These reports indicate that the SAPW is on the move, and doing so rather quickly and aggressively.
In addition to the physical damage the SAPW can inflict on palms directly, it is a primary vector of the nematode that causes Red Ring Disease (RRD), a typically fatal wilt disease of palms. Fortunately, RRD has not yet been detected in SAPWs or palms attacked in the San Diego area.
Infestation Symptoms and Damage Signs:
Currently the most susceptible and targeted host are the Canary Island date palms (Phoenix canariensis), however, the Dactylifera date palms (Phoenix dactylifera) may also be potential targets. Other common landscape palms that could be attacked include California fan palms (Washingtonia filifera), and Mexican fan palms (Washingtonia robusta), all of which have many-leaved canopies and close, tightly packed leaf bases that provide ideal food and shelter.
Early infestation symptoms or signs are very difficult to detect due to the nature of the SAPW feeding. Many cases have shown by the time an infestation is detected and verified it can be too late to save the palm.
Signs to look for:
Early infestations may show “chewed” or cut off leaf tips towards the top of the canopy.
Reduced crown size or distorted “new” growth may be evident. Palms typically lack new center leaves, while the lower “skirt” still appears green. Eventually the green leaves in the lower skirt will die and turn brown.
Leaf bases below the living canopy, may exhibit “holes” made by the SAPW.
Cocoon casings may be found underneath the infested palm.
Larva: Are caterpillar-like, legless, with a head orange-brown with sclerotized mouth parts and a pair of stout, strong mandibles, abdomen creamy white, semi-transparent, each segment bearing tuft of hairs; later instars vary greatly in size, mature larvae.
Pupa: Found inside tough, fibrous, brown, cylindrical, shredded-wheat-like cocoon made from vascular bundles of the host palm.
Adults: Adults are deep black in color. The entire body surface is deeply pitted and is covered with short [hairs]. The insect has a sheen at emergence. The insect then assumes a dull black color for most of its adult life.
Management and treatment:
A judicious detection and monitoring program must accompany any suggested treatment program. Monitoring for any change in appearance is crucial. Insecticide treatments alone do not necessarily guarantee eradication of SAPW. In addition with any suggested treatment, keeping a palm as healthy and vigorous as possible may reduce likelihood of infestation.
- If you are located in a “risk area”, limit unnecessary pruning or cuts to a palm. If removal or pruning of a palm must be made, attempt to do so in late fall to winter (November to February) when adult SAPW activity is much reduced due to cool temperatures. Because of the presence of Fusarium Wilt disease in California the same precautions with pruning tools are suggested.
- Avoid irrigation patterns that maintain the base of the palm trunk and leaf bases in a moist state because soft, moist tissue is more attractive to the SAPW and may facilitate infestation.
- Insecticidal treatments can be made if surrounding environment allows for a safe and proper application. Applications should be made by a licensed and trained professional.
Suggested treatment will consist of a two step application process.
- Insecticidal spraying / drench to the palm canopy, Meristem and the lower petiole bases of all leaves areas will be treated via foliar spray application. This part of the treatment will help provide immediate protection to the leaves.
- Second part of the insecticidal treatment will be a via a soil-applied systemic insecticide which will trans-locate from the roots upwards throughout the palm and incoming tissue will be made. This part of the treatment will provide longer residual control against new feeding.
Suggested treatments are best if made after any pruning or cuts to a palm.
A “preventative” treatment plan can consist of two to three scheduled applications per year. This may prove to be effective in providing year long control.
A big thank you to Donald Hodel (Environmental Horticulturist University of California), Mark Hoddle (Director of Center for Invasive Species Research, Extension Specialist) and their colleagues involved for helping provide pictures and SAPW information used in this document. I acknowledge Donald R. Hodel for the use of his photos from his original article in PalmArbor, which can be found at: http://ucanr.edu/sites/HodelPalmsTrees/files/247345.pdf
For additional information or questions please go to the following websites:
– CISR – Exotic Palm Weevil Symposia – http://cisr.ucr.edu/palm_weevil_symposia.html
– The South American Palm Weevil – A New Threat to Palms in California and the Southwest
– Has the South American Palm Weevil, Rhynchophorus palmarum, Established in Southern California?
– CISR Blog – Mark Hoddle July 24, 2011- http://cisr.ucr.edu/blog/invasive-species/palmaggedon-are-california%E2%80%99s-palms-about-to-face-the-perfect-storm