- Author: Tunyalee Martin
UC ANR Integrated Pest Management Program
A sugar volcano is one symptom that shows your avocado tree might be infected with Fusarium dieback, a fungi spread by a beetle called the shothole borer. But what you might see if your tree is being attacked by shothole borer, varies among the different kinds of tree hosts. The symptoms—staining, sugary exudate, gumming and beetle frass—are often noticed before the tiny beetles (1.5–2.5 mm) are found.
As its name suggests, these beetles bore into trees. Near or beneath the symptoms, you might notice the beetle's entry and exit holes into the tree. The female tunnels into trees forming galleries, where she lays her eggs. Once grown, the sibling beetles mate with each other so that females leaving the tree to start their own galleries are already pregnant. Males do not fly and stay in the host tree.
Shothole borers have a special structure in their mouth where they carry two or three kinds of their own novel symbiotic fungi. Shothole borers grow these fungi in their tree galleries. It's these fungi that cause Fusarium dieback disease, which interrupts the transportation of water and nutrients in the host tree. Advanced fungal infections will eventually lead to branch dieback.
Early detection of infestations and removal of the infested branches will help reduce beetle numbers and therefore, also reduce the spread of the fungus.
- Chip infested wood onsite to a size of one inch or smaller. If the branch is too large to chip, solarize them under a clear tarp for several months
- Avoid movement of infested firewood and chipping material out of infested area
Avocado is one tree host. Shothole borers successfully lay eggs and grow fungi in many tree hosts, with some of these trees susceptible to the Fusarium dieback disease. For more information about tree host species, where the shothole borer is in California, and what symptoms look like in other tree hosts, visit the UC Riverside Eskalen Lab website.
Californians can help in the fight against invasive species by learning and participating during California Invasive Species Action Week, June 2–10.
During the week, spend your lunch with us learning the latest about invasive tree killing pests, aquatic nasties like quagga mussels and nutria, and how the invasive weed/wildfire cycle is altering our ecosystems! http://ucanr.edu/sites/invasivelunch/
Content in this post taken from the UC IPM Avocado Pest Management Guidelines. Faber BA, Willen CA, Eskalen A, Morse JG, Hanson B, Hoddle MS. Revised continuously. UC IPM Pest Management Guidelines Avocado. UC ANR Publication 3436. Oakland, CA.
And more about Shot Hole Borers
http://ucanr.edu/sites/pshb/
- Author: Ben Faber
Los Angeles County Spring 2018 ISHB/GSOB Field Trainings
Registration now open
Learn how to recognize the signs of invasive shot hole borer and gold spotted oak borer infestations in native and landscape trees. Each training will cover how to recognize signs, symptoms, active and inactive populations, take field samples, treatment options, proper handling and disposal of green waste.
- Huntington Gardens, Tuesday May 8, 10:30 - 12:30
training entrance: 1800 Orlando Avenue, San Marino CA 91108
2) O'Melveny Park, Thursday May 17, 10:00 - 12:00
17300 Sesnon Blvd, Granada Hills CA 91344
The events are free, but registration is limited. To register, go to www.pshb.org and click on the calendar entry, or go directly to http://ucanr.edu/sites/gsobinfo/News_and_Events/GSOB_Training_Event_Registration/?editon=0
These trainings were initially offered as part of a series with two live webinars, which have now past – if you did not attend the webinars, unfortunately, these trainings alone will NOT offer CEUs.
AS OF 5/3/2018, THE ONLY FIELD TRAINING WITH SPACE REMAINING IS THURSDAY, MAY 17TH, O'MELVENY PARK, LOS ANGELES COUNTY. IF YOU CANNOT ATTEND THIS TRAINING, DO NOT REGISTER.
- Author: Frank Byrne, Akif Eskalen and Joe Morse
Two closely related Ambrosia beetles (Euwallacea sp.) have been identified in commercial avocado groves in California. The polyphagous shot hole borer (PSHB), detected in Los Angeles, Orange counties and recently in Ventura county, and the Kuroshio shot hole borer (KSHB), detected in San Diego and recently in Orange and Santa Barbara counties, are morphologically indistinguishable, but genetically distinct. Already widespread in a variety of reproductive host trees common in the urban landscape (including box elder, willow, several maples, oak and sycamore species), the beetles represent a significant threat to trees in both landscape and agricultural settings. Adult females construct galleries in the xylem system of host trees, where they cultivate symbiotic fungi (Fusarium, Paracremonium and Graphium spp.) as a food source for their developing young. The fungi are taken up by progeny females in specialized organs within their mouthparts, and transported to other sites within the same tree, where new colonies are established, or to newly colonized hosts. The galleries compromise the structural integrity of infested trees, which can represent a serious safety hazard in urban environments, and disrupt the flow of water and essential nutrients within the xylem. In addition to the physical damage, the fungi extract nutrients from the xylem system, further depriving the tree of nutrients essential for healthy growth and fruit production.
An effective biological control agent is not yet available to manage the SHB in California, and so management for now must rely on the use of chemical pesticides. The control of Ambrosia beetles and their associated fungi using
chemical pesticides is complicated because of their location inside the host trees. The application of insecticides to the external surfaces of trees, where the beetles must first alight prior to boring, has the potential to kill beetles by contact activity, and they may also have the potential to control emerging young adults before they can re-infest the trees.
The drawback of surface treatments is that multiple applications are often required because of the relatively short duration of efficacy. In addition, once the beetle burrows inside the tree, surface treatments are become ineffective. One possible solution to this problem may be the use of systemic pesticides, and scientists at UC Riverside are evaluating the use of both systemic insecticides and fungicides in a 2-pronged attack against the symbiotic system.
Systemic pesticides are mobile within the xylem system of plants, and the fungicides could potentially target the fungi growing in the xylem and deprive the beetle larvae of a food source. The insecticides would prevent the beetle from establishing galleries within susceptible tree hosts, and prevent the survival of beetles and their offspring already present within trees. The big problem with systemic pesticides is getting sufficient concentrations of chemicals to the areas within the trees where the beetle and fungus occur. Although there are exceptions, most systemic treatments are administered to the soil for uptake through the roots. However, in mature avocado groves, the high organic matter content of the soil can prevent effective absorption by roots because the pesticide becomes bound to organic components within the soil. Trunk injection of pesticides directly into the vascular system of trees eliminates the potential for binding of pesticides within the soil, and increases the amount of active ingredient inside the tree available to impact the beetle/fungal system. Systemic pesticides must be formulated for trunk injection and so careful evaluation is needed to ensure optimal efficacy. Trials are being conducted with the assistance of avocado industry and grower collaborators in areas where the SHB has been recorded. The chemicals are injected into the trees using commercially available equipment, and the movement of the active ingredients is then monitored over time in wood core samples taken at different heights of the trees. Two methods are being used to confirm the presence of the chemicals. Insecticides are being quantified using ELISAs that are specific for the active ingredients under investigation. Wood cores taken from trees treated with fungicides are placed in direct proximity to the fungal pathogens growing on agar plates to determine if growth of the fungus is inhibited.
The investigations are still at an early stage, but the researchers are optimistic that they will develop effective control strategies for the SHB that growers can incorporate into their overall pest management programs. Laboratory based bioassays have been used to identify several pesticides that are toxic to the beetle and fungi. The objective of the field trials is to determine whether these chemicals can be utilized as trunk injection agents for the protection of avocado trees. Anyone interested in finding out more about the SHB should go to the web site maintained by Dr. Akif Eskalen at:
http://eskalenlab.ucr.edu/avocado.html
- Author: Ben Faber
At a recent conference in Florida, University of Florida entomologist Daniel Carrillo reported some very disturbing news. There is a fungus/pest complex in Florida avocado and related native laurel species that is similar to a complex found in the California - Shot Hole Borer/Fusarium fungus complex. There it is called Laurel Wilt Disease and is a complex of the ambrosia beetle Xyleborus and the fungus Rafaelea lauricola. It is a fungus/insect complex that causes death in avocado and the relatives of avocado trees. The California complex can cause the death of many tree species, such as sycamore, coast live oak and willow, as well as the decline of avocado. The complex and disease are called Fusarium Dieback here, caused by Euwallacea ambrosia beetle and Fusarium fungus.
What Carrillo and other colleagues have found is that there are similar species to their introduced Rafaelea species of ambrosia beetle that are now attacking live avocado trees. These so-called cryptic species are members of a group of beetles that normally do not attack live trees. These beetles are typically some of the first group of decomposers that go after dead trees. These newly identified insects are morphologically very similar to the original beetle, but are native members of the Florida environment. They too are now attacking live trees. There are now ten potential species of ambrosia beetle that can introduce pathogenic fungi.
To exacerbate the situation, there are other fungi now that have been associated with these beetles that may be similarly as pathogenic as the original fungus. These fungi are genetically distinct from the species causing damage in California. However, this ability of different fungi to adapt to a new invasive beetle species and the ability of other beetle species to pick up the pathogenic fungal species is a scenario that might appear in California.
As the world becomes smaller and more living materials are moved around and they mix, this may be the new reality we are facing.
To read more about the Florida findings check out the article:
http://www.mdpi.com/2075-4450/7/4/55
http://ucanr.edu/sites/socaloakpests/Polyphagous_Shot_Hole_Borer/
- Author: Richard Stouthamer
The recent find of the Kuroshio shot-hole borer in Santa Barbara shows that the beetle is expanding up the coast and it comes on top of the finding earlier this year of a single Kuroshio shot-hole borer in San Luis Obispo. Earlier yet in 2014 a single beetle identified as Euwallacea fornicatus was found by the CDFA monitoring in Santa Cruz county, unfortunately this specimen was only identified using morphological characters and therefore we do not know which of the three cryptic species of the Euwallacea fornicatus species complex we are dealing with for that particular find. After the single find (2016) in San Luis Obispo a several additional traps were placed in the vicinity of the first find but no additional beetles have been caught. In a single location in Irvine KSHB has also been detected last year (2015). Recently, the Kuroshio Shot-hole borer has also been reported in Tijuana Mexico, which is not surprising since the heavily infested Tijuana river valley park in San Diego county is less than 0.6 miles from the border with Tijuana. It is clear from these detections that the KSHB is on the move, just like the PSHB. These long distance moves by the beetles are most likely caused by human transport, and the most likely culprit is wood transported after trees have been cut down or trimmed. Both in San Luis Obispo and the location in Santa Cruz no additional finds have been reported, often the density of insects following an invasion of a new area remains low while the population is expanding and followed by it reaching such levels that they are “suddenly” detected in many locations.