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Palm weevil threatens So Cal palm trees
More than 20,000 palms in the region have been killed by South American palm weevil
The swaying palm trees that line San Diego's streets might not be swaying much longer due to a pest that is infecting many of these iconic trees and making its way across Southern California.
The South American palm weevil (SAPW), also referred to as the American palm weevil and black palm weevil, was first detected in San Diego County in 2011, with breeding populations found in a Canary Island date palm in San Ysidro in 2015. According to industry experts, more than 20,000 palms in the region have been killed by SAPW thus far.
While SAPW can attack a variety of palm tree species, Canary Island date palms (Phoenix canariensis) are by far their most preferred host. SAPW adults lay their eggs in the crown of palm trees and then larvae hatch and voraciously consume the growing tissue of the palm. If left unchecked, this pest can kill mature palms in a matter of months.
SAPW has affected neighborhoods and cities throughout the greater San Diego area, creating a need for more residents to be aware of this concern and report infected palms. Though infestation has not been confirmed, SAPW adults have been reported in the Coachella Valley – about 120 miles northeast of San Diego.
‘Super-dispersers' from San Diego can fly long distances
The California Department of Food and Agriculture has trapped weevils in the Coachella Valley and recent posts on iNaturalist, a social network for community members to map and share observations of biodiversity across the globe, indicate that adult weevils are flying into areas where edible dates are grown.
These reports interest researchers like Mark Hoddle, University of California Cooperative Extension based at UC Riverside, because the Coachella Valley, the major production area for edible dates nationwide, is far from any known infested palm trees.
How did the weevils get there? “It may be super-dispersers from San Diego,” said Hoddle. “They are on a death mission when they fly long distances – find food or die trying!”
While conducting an experiment to assess SAPW's flight capability, Hoddle and his team learned that the beetle could fly non-stop for up to five hours, with some variation between males and females. “In some cases, they will fly until they die,” Hoddle said.
Currently, Hoddle is managing an ongoing urban palm surveillance effort of 521 palm trees in and around Bonita in San Diego County, which are assessed every six months. More than 70% of these palms have been killed by SAPW over a 6.5-year period.
Although Canary Island date palms are highly preferred by SAPW, the weevils can complete their entire life cycle in sugarcane as well. For palm species that are not currently preferred by the pest, there is still a chance that they can become more preferred over time as SAPW works its way through all available Canary Island date palms in the region.
Taking action to protect your palms
There are steps that one can take to protect palm trees. Traps can be used to both monitor weevils and reduce the number of adults flying around. There are two types of traps that Hoddle has evaluated for weevil captures: the bucket trap and the Picusan trap. Both use a fermenting bait – prepared with dates, baker's yeast and water – that is placed in a glass jar with a perforated lid, in addition to a commercially available aggregation pheromone that will attract male and female weevils.
Of the two trap types, Hoddle prefers Picusan traps because they catch about six times as many weevils as bucket traps – retaining more than 95% of the weevils that are attracted to them. Bucket traps, on the other hand, retain only about 30% of weevils.
Hoddle emphasizes that trap placement is key. The Picusan trap is designed to be placed on the ground, whereas the bucket trap is typically hung from a tree branch, fence or post. Furthermore, the traps should be placed at least 500 yards away from the potential host palms and avoid direct sunlight. Shaded or partially shaded areas are best to avoid diminishing the trap's potency.
Another strategy is to prune palm trees when SAPW flight activity is low (December through March) to minimize attracting flying adult weevils to freshly pruned palms.
Finally, the best way to protect your tree is to apply insecticides. These chemicals will kill adult weevils that attempt to start infestations. While contact insecticides can deter and kill adults when applied to the crown of the palm, systemic insecticides are usually more effective and can be applied as soil and crown drenches, trunk sprays, or soil and trunk injections. Systemic insecticides move inside the palm and concentrate in the palm heart, the growing area at the top of the palm where weevils feed. Once this growing area is damaged by feeding weevil larvae, palms die.
“Just know that if you are planning to protect palms with insecticides, you are in it for life,” saidHoddle, emphasizing that there is no “one and done” approach to saving palms affected bySAPW. “Don't start if you can't commit.
Aesthetics aren't the only motivation to prevent palm infection and death caused by SAPW. Palm crowns that are highly damaged by larval feeding can detach from the top of the trunk and fall to the ground, putting people and property at risk. Dead fronds drop from dying palms and the large spines at the base of the fronds are a significant hazard to people and pets.
Seek expert support for tree concerns and removal
Removing dead palms is an expensive and time-consuming process. Removal can cost between $2,400 to $4,000 per palm, with cost varying based on location. For example, if a palm is in an area that requires the use of a crane, semitruck or helicopter to safely access, remove and dispose of the dead palm, tree removal can cost up to $15,000.
Once a palm is infested with SAPW, it likely cannot be saved unless it is aggressively treated with insecticides at an early stage of the infestation. If you are certain that a tree is infected by SAPW, it is highly recommended that you work with a tree care company or arborist to manage the weevils that might be present in the palm and to promptly and responsibly dispose of dead palms so that spread of weevils into new areas is minimized.
To confirm visual signs of palm trees that have been affected by SAPW, visit Hoddle's site for more information and to report infested palms: https://cisr.ucr.edu/invasive-species/palmarum-survey.
To read this story in Spanish, visit: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=58381
Invasive pests kill thousands of trees, but scientists see some successes
Early detection increases the chances of eradicating pests
Trees provide shade to keep us cool, produce oxygen for us to breathe and calm our nerves. Numerous studies have demonstrated that even brief contact with trees and green spaces can provide significant human health benefits such as reductions in blood pressure and stress-related hormones. Trees also reduce noise and visual pollution, help manage storm water runoff, reduce erosion and provide habitat for birds and wildlife. Trees naturally capture carbon, helping to offset the forces of climate change. They also increase the value of our properties and communities. In short, trees are essential to our well-being.
Unfortunately, invasive pests pose an ongoing threat to California's forests in both urban and wildland settings. Invasive insects such as goldspotted oak borer and invasive shothole borers have killed hundreds of thousands of trees in Southern California and are continuing to spread. Meanwhile, other pests and diseases such as Mediterranean oak borer and sudden oak death are killing trees in Northern California.
While the situation may sound dire, it is not hopeless. Of course, the best way to stop invasive pests is to prevent them from entering the state, as the California Department of Food and Agriculture has done on many occasions. For example, several months ago, CDFA border inspectors seized a load of firewood containing spotted lanternfly eggs (a pest that is causing extensive damage on the East Coast). When pests do sneak in, the next defense is to catch them early before they become established. Finally, even if pests do become established, they can be managed if not completely eradicated.
A few examples may help to illustrate why invasive tree pests deserve action, but not panic.
Red striped palm weevil eradicated in Laguna Beach
When red striped palm weevil, a highly destructive palm pest native to Indonesia, was discovered in Laguna Beach in October 2010, a working group was quickly formed to develop a management plan. The small but diverse group included international palm weevil experts, research scientists from University of California Riverside, CDFA and U.S. Department of Agriculture, UC Cooperative Extension personnel from San Diego, Orange and Los Angeles counties and county entomologists from the agricultural commissioner's offices in Orange and San Diego counties.
The resulting response included a pheromone-based trapping program, public advisory and targeted insecticide treatments. Within two years, additional trapping and inspections could not find any signs of continued infestations. Early detection was key to the success: the infestation in Laguna Beach was identified early, so the weevil population was still relatively small. In addition, Laguna Beach is geographically isolated, the local climate is much cooler than the weevil's place of origin, and the eradication effort was well funded by state and federal agencies. Eliminating invasive pests where such conditions are not present may prove more difficult.
Invasive shothole borers attack Disneyland
The Disneyland Resort in Anaheim contains 16,000 trees and over 680 different tree species. When park officials identified an infestation by invasive shothole borers in 2016, their initial attempts at vanquishing the insects with pesticides produced mixed results. Then, they consulted with experts from UC Riverside and UC Cooperative Extension and together designed and followed an integrated pest management program that included monthly ground surveys, a trapping program that helped to detect infestation hot spots and find and remove the source of beetles, and occasional pesticide treatments on selected trees. The park went from a large number of beetles in 2017 to very low levels today. There are still some beetles, but resulting damage is extremely low, and although monitoring programs continue, the park's landscape team has been able to turn its focus elsewhere.
Goldspotted oak borer spotted in Weir Canyon
When goldspotted oak borer was confirmed in Orange County's Weir Canyon in 2014, a team from Irvine Ranch Conservancy, the organization that manages the area on behalf of Orange County Parks, sprang into action. UC Cooperative Extension and the US Forest Service assisted IRC in developing a management program, and over the ensuing years, IRC has actively collaborated with OC Parks, The Nature Conservancy, OC Fire Authority, and CAL FIRE to control the existing infestation and stop its spread. IRC has surveyed the oaks in the area yearly to monitor the infestation and guide each year's management actions.
To reduce the spread of the infestation, IRC removed more than 100 severely infested oaks in the first few years of management (no severely infested oaks have been found in the last few years of surveys). Additionally, more than 3,000 tree trunks have been sprayed annually in the late spring to kill emerging adult beetles and newly hatched offspring.
In the most recent survey of the oaks in Weir Canyon, the IRC team found only 12 trees with new exit holes, and most of those had just one to two exit holes per tree, which is an extremely low number. With the situation well under control, IRC is now considering modifying its annual spraying program and adapting other less aggressive treatment options. Finally, IRC has been actively planting acorns to mitigate losses due to the removals as well as the Canyon 2 Fire of 2016.
As these brief examples demonstrate, insect pest infestations can be managed or even eradicated if caught early enough. Early detection not only increases the chances of success, but also minimizes the cost of pest management efforts.
What you can do to prevent infestation
While management actions will vary depending on the insect or disease, species of tree and location, there are a few steps that will lead to greater success in fighting tree pests and diseases.
- Keep your trees healthy. Proper irrigation and maintenance go a long way toward keeping trees strong and resistant to pests and diseases.
- Check your trees early and often for signs and symptoms of tree pests and diseases. These may include entry/exit holes, staining, gumming, sugary build-ups, sawdust-like excretions, and branch or canopy dieback. Use available tools like the UC IPM website to determine probable causes of the problems.
- Talk with experts (arborists, pest control advisers, researchers and advisors from the University of California and other institutions), and report pest findings to your county Agricultural Commissioner.
- Evaluate the extent of tree damage and determine a management plan. Remove severely infested branches and trees that may be a source of insect pests that can attack other trees.
- Properly manage infested wood and green waste. Chip wood and other plant materials as small as possible. Solarization or composting can further increase the effectiveness of chipping. It is generally best to keep those materials close to where they originated, but if you absolutely need to move them, first make sure the facility where they will be sent is equipped to process them. Always tightly cover materials while in transit. If working with a tree care professional, insist that proper disposal is part of the job requirements.
- Many invasive tree pests can survive in down wood for long periods. When buying or collecting firewood, always obtain it as close as possible to where you are going to burn it and leave leftover firewood in place.
The scent that could save California’s avocados
Scientists search for pheromone to disrupt insect mating
UC Riverside scientists are on the hunt for a chemical that disrupts “evil” weevils' mating and could prevent them from destroying California's supply of avocados.
Avocado weevils, small beetles with long snouts, drill through fruit to lay eggs. The weevil grubs or larvae bore into avocado seeds to feed, rendering everyone's favorite toast topping inedible.
“They're extremely hard to control because they spend most of their time deep inside the fruit, where they're very well protected from insecticides and natural enemies,” said UCR researcher Mark Hoddle, a UC Cooperative Extension entomology specialist.
Not only are the insects reclusive, they are also understudied, making information about them hard to come by. “All books on avocado pest management will tell you these weevils are bad. They're well recognized, serious pests of avocados, but we know practically nothing about them,” Hoddle said.
One strategy for controlling pests is to introduce other insects that feed on them. However, that is unlikely to work in this case. “Natural enemies of these weevils seem to be extremely rare in areas where this pest is native,” Hoddle said.
To combat avocado weevils in Mexico, an area where they are native, and to prevent them from being accidentally introduced into California, Hoddle is working with Jocelyn Millar, a UCR insect pheromone expert. They are leading an effort to find the weevil's pheromone, with the goal of using it to monitor these pests and prevent them from mating in avocado orchards.
Pheromones are chemicals produced and released into the environment by an insect that can be “smelled” by others of its species, and affect their behavior.
“We could flood avocado orchards with so much pheromone that males and females can't find each other, and therefore can't reproduce,” Hoddle said. “This would reduce damage to fruit and enable growers to use less insecticides.”
Alternative control strategies could include mass trapping, using the pheromone as a lure, or an “attract-and-kill” approach, where the pheromone attracts the weevils to small sources of insecticide.
The work to identify, synthesize and test this pheromone in the field is supported by grants from the California Department of Food and Agriculture, as well as the California Avocado Commission.
An initial phase of the project sent Hoddle to a base of operations three hours south of Mexico City, an area with large weevil populations. Using a special permit issued by the USDA, Hoddle brought weevils back to UCR's Insectary and Quarantine facility.
Hoddle and Sean Halloran, a UCR entomology researcher, captured the chemicals that avocado weevils release into the air. Possible pheromone compound formulas were identified from these crude extracts and are now being synthesized in Millar's laboratory.
“Weevil pheromones have complicated structures. When they're made in a lab, they can have left- or right-handed forms,” said Hoddle. Initially, Millar's group made a mixture of both forms to see if the blend would work as an attractant, as it is far cheaper to make the blend than the individual left- or right-handed forms.
Field work in Mexico with the pheromone cocktail by Hoddle, his wife Christina Hoddle, an associate specialist in entomology, and Mexican collaborators did not get a big response from the weevils, suggesting that one of the forms in the blend could be antagonizing the response to the other.
As the next step, the researchers plan to synthesize the individual forms of the chemicals and test the insects' response to each in Mexican avocado orchards.
Because the levels of avocado imports from Mexico are increasing, the risk of an accidental weevil invasion is rising as well. Hoddle is hopeful that the pheromone will be successfully identified and used to lower the risk this pest presents to California's avocado growers.
“We've been fortunate enough to be awarded these grants, so our work can be implemented in Mexico and benefit California at the same time,” Hoddle said. “The tools we develop now can be used to make sure crops from any exporting country are much safer to import into California.”
Who's Speaking at the UC Davis Entomology/Nematology Seminars?
Talk about a full schedule! Nematologist Shahid Siddique, assistant professor, UC Davis...
The yellow fever mosquito, Aedes aegypti, will be the topic of a UC Davis Department of Entomology and Nematology seminar on Jan. 12. (Photo courtesy of the Center for Disease Control and Prevention)
The alfalfa weevil, Hypera postica, will be discussed at the Jan. 5 seminar hosted by the UC Davis Department of Entomology and Nematology. (Wikipedia photo by AfroBrazilian)
South America palm weevil is killing palm trees in Southern California
South American palm weevils that have made their way north from Mexico are having a destructive impact on palm trees in the San Diego region, reported Abbie Alford on CBS News 8 TV in San Diego.
UC Cooperative Extension specialist Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside, toured the reporter through the hard-hit Sweetwater Reserve in Bonita, where 10 percent of the palms die every three months.
“We are going to see hundreds, thousands of Canary Island Date Palms die over the next couple of years,” he said.
The weevils use their protruding noses to drill holes in the palm, where females lay their eggs.
San Diego County Agriculture, Weights and Measurements said it plans to remove 50 infested Canary Island Palms from the Sweetwater Regional Park and is educating arborists about the invasive pest.
A spokesperson for the City of San Diego said it is working with UC Cooperative Extension.
