Posts Tagged: Oak Borer
Invasive pests kill thousands of trees, but scientists see some successes
Reposted from UC ANR news Early detection increases the chances of eradicating pests Trees...
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.
New Invasive Insect: Mediterranean Oak Borer
The Mediterranean oak borer (Xyleborus monographus), or MOB, is an invasive ambrosia beetle that was first collected from declining oak trees (Quercus spp.) near Calistoga (Napa County) in 2019 (Fig 1). Subsequently in early 2020, the beetle was detected in the neighboring counties of Lake and Sonoma, and more recently a separate infestation was discovered in suburbs near Sacramento. MOB is native to the Mediterranean regions of Europe, the Middle East, and North Africa and was likely introduced to North America in infested wood material. Within its native range MOB is a pest primarily of dead and dying oaks. In California, MOB has been detected in valley oak (Q. lobata) and blue oak (Q. douglasii). Given the cryptic nature of the insect, the extent of the infestations, and presence of dead trees with evidence of the beetle, the insect has likely been in California for more than five years.
Ambrosia beetles are interesting insects because they carry symbiotic ambrosia fungi which they cultivate along their galleries (boring tunnels) for food. Most ambrosia fungi are weak pathogens (typically only colonizing the tissue near the galleries), but a fungus associated with MOB, Raffaelea montetyi, appears to cause wilt disease in cork oaks in Portugal. This fungus and several others associated with MOB, have been recovered from infested trees in California and research is underway to determine if these ambrosia fungi could cause similar diseases in North American oak species.
MOB appears to initially attack the canopy of host trees where it kills branches, with persistent infestations spreading to the main stem and eventually killing the tree (Fig. 2). The extensive network of MOB galleries can weaken trees and make them more susceptible to failure. Thus far, trees in California with MOB infestations appear to have been stressed by other biotic and abiotic factors prior to MOB colonization, so it is unclear if the insect and its ambrosia fungi can infest and kill healthy trees.
Signs of MOB infested trees are declining canopies, tiny exit holes and boring dust in cracks of the bark, and occasionally sap flux; however, these symptoms could be caused by other boring insects or diseases. The best way to detect MOB infested trees is to observe the pattern of canopy decline. MOB begins by colonizing a large branch in the upper canopy, so newly infested trees will often have one declining branch while the rest of the canopy appears healthy. As the infestation progresses, the entire canopy begins to decline and in some instances, heavily infested branches can produce extensive epicormic sprouting with leaves diminished in size and densely clustered (sometimes referred to as “popcorn foliage”). The most reliable way to confirm MOB is from the architecture of its galleries, which are trellis-like, intersecting, and fan out in a single plane (Fig. 3A). These gallery patterns distinguish it from native Monarthrum spp. of ambrosia beetles, which have galleries branching from a single point and do not intersect neighboring galleries (Fig. 3B). These native beetles will only attack trees that are already dead, dying, or diseased.
Research is currently underway to determine the extent of the two infestations and to find effective management strategies to control MOB. From other similar invasive insects, such as the shot hole borer in southern California, options like chipping (≤1” size), solarization, burning, or burying infested material will likely be crucial in mitigating spread. However, since infestations can be cryptic for several years, there is significant potential for the beetle's range to expand as they can be moved in infested wood and are capable fliers. The best method of control is preventing the movement of the insect and its host material from known infested areas. For more information, please visit: ucanr.edu/sites/mobpc.
If you have a tree that you believe to be infested, please contact the California Department of Food and Agriculture:
- Pest Hotline: 1-800-491-1899
- Report a Pest: cdfa.ca.gov/plant/reportapest/
Michael I. Jones, PhD, UC Cooperative Extension Forest Advisor, Mendocino, Lake, & Sonoma County, mjones@ucanr.edu, (707) 463-4495
New Invasive Insect: Mediterranean Oak Borer
The Mediterranean oak borer (Xyleborus monographus), or MOB, is an invasive ambrosia beetle that...
Fig1 MOB female closeup
Invasive pest spotlight: Goldspotted Oak Borer
Goldspotted oak borer. First identified in eastern San Diego County in 2004, the goldspotted oak...
Photo Adult female (left) and male (right) goldspotted oak borers. [Photo by Michael Jones, UC Davis]