Two palm tree weevils found in California have some nursery stock producers and date growers on edge over the potential spread of the pests and how possible quarantines could jeopardize future plant shipments.
The pests include the red palm weevil (RPW), Rhynchophorus ferrugineus, and the South American palm weevil (SAPW), Rhynchophorus palmarum. The weevils are economic threats to California’s palm nursery and date industries.
Red palm weevil
Last August, agriculture officials confirmed the first U.S. detection of the RPW in a dying Canary Island date palm at a residence in Laguna Beach (Orange County). The palm was safeguarded, removed, quartered, examined, and destroyed.
The weevil, native to Southeast Asia, is considered the worst palm tree pest in the world.
The most shocking impact from weevil feeding occurs when the tree top falls over. Other symptoms include droopy, smaller and yellowed palm leaves. Tunnels and brown fluid are found at base of the frond petiole.
The RPW is attracted to unhealthy palms, but also attacks healthy palms. Primary hosts include 24 species of palm.
The female RPW bores into the palm tree laying up to 250 eggs over a lifetime. The eggs hatch in about three days. The voracious larvae feed in the apical growing point of the palm reducing the ability to transport nutrients and water to the crown. Reddish-brown adults are 1.4 to 1.6 inches in length.
The California Department of Food and Agriculture has placed 144 traps in Orange County; most in the Laguna Beach area. The pheromone bucket traps are checked weekly.
There have been reports of additional RPW finds in the same area which would normally trigger a USDA-Animal and Plant Health Inspection Service (APHIS) quarantine.
Larry Hawkins, APHIS spokesman in Sacramento, Calif., says a single insect was found in the initial find in Laguna Beach by agriculture officials. Other RPW insects found by residents were hand-delivered to agriculture officials. Hawkins says those insects do not officially count to APHIS. Officials must capture an insect on or inside the palm tree to be declared an official detection.
“The federal order (quarantine) trigger for this insect would be finds of two insects of any life stage (either sex) within one life cycle within 3 miles distance of each other,” Hawkins said. “We haven’t met the trigger. We officially only have one insect.”
APHIS has prepared a draft quarantine document in case other RPWs are found.
If the official RPW trigger is met, Hawkins says the quarantine would likely include restrictions on the movement of host material and waste products, plus an inspection of nursery palms grown for shipment.
South American palm weevil
A South American palm weevil was found May 11, in San Ysidro, a community located in southern San Diego just miles from the Mexican border. This was the first find in the U.S. Several additional SAPWs were found close by in July, says San Diego County Agricultural Commissioner Lisa Leondis.
“The South American palm weevil is a bad pest of palms,” Leondis said. “You can look at a 30-foot palm tree and have no idea the pest is inside. The pest really doesn’t come out much until the tree dies and the top falls off.”
The SAPW is a major pest of oil and coconut palms which can result in tree death. Palm hosts include the date, Canary Island date, coconut, African oil, sago, and Washingtonia fan palms.
Adult insects are completely black sometimes with a velvety-appearance. Adults are 1.5 to 2 inches in length and live for about 40 days.
Female SAPWs deposit eggs into bored holes near palm leaf bases or damaged areas. The holes are sealed with a brown waxy secretion. An average of 245 eggs is laid over the insect’s lifetime with egg hatch in about three days. Like the RPW, larvae damage the tree by feeding on palm tissue in the crown - destroying the apical growth area.
The SAPW is a vector for the red ring nematode, Bursaphelenchus cocophilus; the causal agent of red ring disease of coconut. Tree death can occur five months after inoculation. None of the SAPW captured in San Diego County carried the nematode, Leondis says.
One of the difficulties with this pest is trapping so close to the Mexico border.
“We really don’t have the ability to go full circle around the pest and trap for it,” Leondis said. “We can only trap on the California side of the border.”
CDFA has 315 SAPW traps in San Diego County - 290 in San Ysidro and 25 in Vista. Two traps are placed in neighboring Imperial County.
The nursery plant industry is very disturbed by the weevil findings. In San Diego County, ornamental trees and shrubs, including palm trees, are a $300 million business annually. Most San Diego County nurseries grow palm trees.
An APHIS-SAPW quarantine in San Diego County is inevitable, according to Jim Bethke, University of California Cooperative Extension nursery and floriculture farm adviser in San Diego County. Bethke believes a quarantine would significantly hinder the movement of palms from the quarantined areas.
“The quarantine would likely require nursery growers to hold all palms in the nursery in the quarantine area for at least a year before the plants could be sold,” Bethke said. “During that time pesticide treatments would be required on the palms.”
There is also talk of requiring nursery producers to build screened structures to house palm stock for protection from the pest.
“Screening structures would be extremely expensive for nursery palm producers. The vast majority of them would not be able to afford it,” Bethke said. “Many producers would either stop growing palms or go out of business. That would more or less move palm production industry out of San Diego County.”
Bethke believes agricultural research can provide effective control measures for both weevils. Finding answers would require time and funding. Yet Bethke says dollars for agricultural research across California are limited. Today, dollars are only available for the most “serious” pests.
“The Asian citrus psyllid came along several years ago in California and the dollars to fight the diaprepes root weevil just disappeared,” Bethke said. “If we don’t have the funding to fight the palm weevils, we could battle the pests for a very long time.”
California commercial date production, valued at $51 million in 2009, is centered in the southern interior valleys. Date farmers in the Coachella Valley in Riverside County produce two thirds of the state’s crop. The remainder is grown in Imperial County; mostly in the Bard-Winterhaven area.
Dates are also grown in neighboring Yuma County, Ariz.
The Keck family owns and operates Hadley Date Gardens in Thermal in the Coachella Valley. Albert Keck is a third-generation date grower and is concerned about the weevil threats.
“The weevils could be devastating if they are not contained and spread into the date-growing areas,” said Keck, who also serves as chairman of the California Date Commission (CDC).
Keck is optimistic that weevil containment will occur.
“Sometimes an evasive pest is found but does not become established. Hopefully that will be the case,” Keck said. “The state of California is aggressively working to contain and eradicate the pests.”
Keck says palm trees are iconic to California and are found in residential, public, and agricultural areas. This makes the weevils a statewide issue. Statewide funds should be utilized to fight the pests; not just dollars from the agricultural industry.
To report a pest, call the California Pest Hotline at (800) 491-1899 or go online to www.cdfa.ca.gov/go/reportapest.