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
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.
Ambrosia beetles comprise a group of over 6,000 species in the Scolytinae subfamily. Most of these beetles typically attack decomposing and dead trees. The Polyphagous/Kuroshio Shot Borers have been reports on over 300 landscape and wildland living tree species, including avocado. Decline and death of trees has been noted in California since 2012, and the full economic extent is still unclear. The beetles feeds on a fungal symbiont that is introduced into the tree, and it is the fungus that spreads throughout the tree and causes the tree decline and death.
What was once thought to be another species of beetle (Tea Shot Hole Borer) and then identified as a new species - Polyphagous Shot Hole Borer- and now expanded to include another species of borer – Kuroshio Shot Hole – is showing that its fungal partners can be quite diverse. A recent publication indicates the increasing tangled association of the shot hole borer/disease complex that is affecting avocado and other tree species.
Two Novel Fungal Symbionts Fusarium kuroshium sp. nov. and Graphium kuroshium sp. nov. of Kuroshio Shot Hole Borer (Euwallacea sp. nr. fornicatus) Cause Fusarium Dieback on Woody Host Species in California
Francis Na, Joseph D. Carrillo, Joey S. Mayorquin, Cedric Ndinga-Muniania, and Jason E. Stajich, Department of Plant Pathology and Microbiology, University of California, Riverside, 92521; Richard Stouthamer, Department of Entomology, University of California, Riverside, 92521; Yin-Tse Huang, Department of Plant Pathology, National Chung Hsing University, Taichung 402, Taiwan, ROC, and School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, Gainesville; Yu-Ting Lin and Chi-Yu Chen, Department of Plant Pathology, National Chung Hsing University, Taichung 402, Taiwan, ROC; and Akif Eskalen,† Department of Plant Pathology and Microbiology, University of California, Riverside, 92521
Shot hole borer (SHB)-Fusarium dieback (FD) is a new pest-disease complex affecting numerous tree species in California and is vectored by two distinct, but related ambrosia beetles (Euwallacea sp. nr. fornicatus) called polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB). These pest-disease complexes cause branch dieback and tree mortality on numerous wildland and landscape tree species, as well as agricultural tree species, primarily avocado. The recent discovery of KSHB in California initiated an investigation of fungal symbionts associated with the KSHB vector. Ten isolates of Fusarium sp. and Graphium sp., respectively, were recovered from the mycangia of adult KSHB females captured in three different locations within San Diego County and compared with the known symbiotic fungi of PSHB. Multigene phylogenetic analyses of the internal transcribed spacer region (ITS), translation elongation factor-1 alpha (TEF1-α), and RNA polymerase II subunit (RPB1, RPB2) regions as well as morphological comparisons revealed that two novel fungal associates Fusarium kuroshium sp. nov. and Graphium kuroshium sp. nov. obtained from KSHB were related to, but distinct from the fungal symbionts F. euwallaceae and G. euwallaceae associated with PSHB in California. Pathogenicity tests on healthy, young avocado plants revealed F. kuroshium and G. kuroshium to be pathogenic. Lesion lengths from inoculation of F. kuroshium were found to be significantly shorter compared with those caused by F. euwallaceae, while no difference in symptom severity was detected between Graphium spp. associated with KSHB and PSHB. These findings highlight the pest disease complexes of KSHB-FD and PSHB-FD as distinct, but collective threats adversely impacting woody hosts throughout California.
The following is the abstract of a recent article highlighting the occurrence of the invasive shot hole borer that is found in California and described in our blog site:
Invasive species are a problem world-wide and this is an example of how invasives can arrive in multiple countries at the same time and/or how possibly they might move from somewhere like California to another far away country like South Africa. People are the usual agents for carrying these pests around the world.
The polyphagous shot hole borer (PSHB) and its fungal symbiontFusarium euwallaceae: a new invasion in South Africa
The polyphagous shot hole borer (PSHB), an ambrosia beetle (Coleoptera: Curculeonidae: Scolytinae) native to Asia, together with its fungal symbiont Fusarium euwallaceae, has emerged as an important invasive pest killing avocado and other trees in Israel and the United States. The PSHB is one of three cryptic species in the Euwallacea fornicatusspecies complex, the taxonomy of which remains to be resolved. The surge in the global spread of invasive forest pests such as the PSHB has led to the development of programs utilizing sentinel tree plantings to record new host-pest interactions. During routine surveys of tree health in botanical gardens of South Africa undertaken as part of a sentinel project, an ambrosia beetle/fungal associate was detected damaging Platanus x acerifolia(London Plane) in the KwaZulu-Natal National Botanical Gardens, Pietermaritzburg.
Identification of the beetle by sequencing part of the mitochondrial cytochrome oxidase c subunit 1 (COI) gene confirmed its identity as PSHB, and specifically one of the invasive haplotypes of the beetle. The associated fungus F. euwallaceaewas identified based on phylogenetic analysis of elongation factor (EF 1-α) sequences. Koch's postulates have confirmed the pathogenicity of fungal isolates toP. x acerifolia. This is the first report of PSHB and its fungal symbiont causing Fusarium dieback in South Africa. This report also represents the first verified case of a damaging invasive forest pest detected in a sentinel planting project, highlighting the importance of such studies. Given the potential impact these species present to urban trees, native biodiversity and agriculture, both the PSHB and its fungal symbiont should be included in invasive species regulations in South Africa.
The full paper is at:
Photo: Infected sycamore which is related to London plane tree.
A recent publication from CA Fish and Wildlife has some wonderful photos of trees that have been known to be attacked by either or both of the Shot Hole Borers, Polyphagous or Kuroshio. The publication can be found at:
The most current listing of hosts and the distribution of the beetles can be found at Akif Eskalen's website:
Shot hole borers (SHB) and Fusarium dieback (FD) represent an increasing threat to many plant species in southern California. Two similar species of invasive shot hole borer exist in southern California, the Polyphagous shot hole borer (PSHB) and the Kuroshio shot hole borer (KSHB) (Euwallacea spp). Shot hole borers are ambrosia beetles forming a symbiotic relationship with the fungi. PSHB symbionts are Fusarium euwallaceae, Graphium euwallaceae, and Paracremonium pembeum, while KSHB forms a symbiotic relationship with two novel species of Fusarium and Graphium (Cooperband et al. 2016) (Lynch et al. 2016) (Eskalen, Stouthamer 2015). These fungi clog the host's vascular tissue leading to branch dieback and eventually tree death. The beetles are not pathogenic in their native habitats in Southeast Asia, preferring instead to infect stressed trees (Hulcr and Dunn 2011). The two shot hole borer species found in southern California differ primarily in the fungal species they associate with but can be treated the same for the sake of management.
SHB infestations begin when females burrow natal galleries into the host, introduce symbiotic fungi, and lay eggs. Females are capable of producing haploid male offspring in the absence of mating while mated females produce diploid female offspring. Eggs mature into adults in six weeks. Beetle emergence occurs over a period of weeks during the spring and summer. Dispersal of females to other hosts is primarily wind-driven, but is also likely facilitated by firewood and green waste movement. Males are incapable of flight; they remain on the host tree but may enter other natal galleries (Umeda, Eskalen, and Paine 2016). Beetle dispersal can occur over large distances if winds allow.
The loss of wildland trees, particularly in riparian areas, poses a threat to numerous threatened and endangered species such as the least Bell's vireo (Vireo bellii pusillus). Destroyed forests give way to invasive species such as giant reed (Arundo donax) and castor bean (Ricinus communis) (Boland 2016). Specifics of this emerging threat are poorly understood and while research is ongoing this guide is intended as an identification aid for land managers in areas where SHB may not yet be discovered.
(references are found at the end of the publication)
- Author: Sonia Rios
During the first week of August, the California Avocado Society, Inc., California Avocado Commission, University of California Cooperative Extension hosted six Laurel wilt researchers from the University of Florida. The speakers were Randy Ploetz, Jonathan Crane, Bruce Schaffer, Daniel Carrillo, Jeff Wasielewski and Edward Evans. In addition to talking at all three seminar locations, San Luis Obispo, Ventura, and Fallbrook, the researchers were also able to tour the major avocado growing regions.
Laurel wilt is a deadly disease of redbay (Persea borbonia) and other tree species in the Laurel family (Lauraceae), which includes the avocado tree. The disease is caused by a fungus (Raffaelea lauricola) that is introduced into host trees by a nonnative insect, the redbay ambrosia beetle (Xyleborus glabratus). Native to Southeast Asia, the ambrosia beetle has similarities to our current ambrosia pest, Polyphagous shot hole borer and the Kuroshio Borer. That is why this visit from our fellow extension researchers from the University of Florida. However the fungus associated with Laurel Wilt is unlike the disease here in California. Laurel Wilt is a disease that that causes a reaction in the tree to restrict water flow in the tree and the tree collapses rapidly. The tree dies so fast that it doesn't even have a chance for the leaves to fall of the dead branches.
The beetle has the ability to spread the specific pathogen to other ambrosia beetle vectors which happens when they feed on infected trees. Sanitation is the most effect way to manage this problem. Scouting for wilted branches and their rapid removal has been the key to early intervention and eradication. Dr. Ploetz suggests removing the tree immediately. By the time you see frass and streaks in the wood, the tree is already infected and has been for sometime. As soon as a growers see the wilt in the branches, its time to move quickly. This disease may be mistaken for Verticillium wilt or Phytophthora. It can spread throughout the grove by root grafting.
The generation time for the beetle inside avocado trees takes about 40-50 days depending upon temperatures. Their flight activity is highest in the late afternoon and early evening. Dr. Carrillo mentioned that ambrosia beetles are notoriously difficult to control because they are inside the tree most of their life cycle versus being outside the tree. Contact herbicides will not work, because the insects are primarily inside the tree. One of the first goals to avoid infection, is to keep your trees healthy. A sick tree is more attractive
Scouting for laurel wilt in commercial avocado groves
1. Surveying for the symptoms of laurel wilt is a key component of limiting the spread of laurel wilt. Growers and their workers should survey their groves immediately and then weekly or more often if an infestation is detected in an adjacent grove. Pathogen sniffing dogs are currently being used, however there are less than half-dozen trained dogs for this purpose. Symptoms to look for might include:
i. Leaf and young stem wilting.
ii. Leaf color changing from light green to dark green, bluish-green or greenish-brown. Some leaves showing leaf mottling (dark and light green areas) and yellowing.
iii. Dead leaves curled hanging on the tree.
iv. A few stems and limbs with 2 to 4 ft of dieback or whole sections or entire limbs with dieback.
v. Inspection of the trunk and major limbs may show dried sap (white, crystalline powdery material) that indicates insect boring. In any case, on symptomatic limbs remove the bark down to the sapwood and look for dark streaking. Dark streaks in the sapwood may indicate fungal infection. Normally this sapwood should be white to yellowish with no dark staining or streaking. In addition, small, dark holes in the sapwood further indicate wood boring beetles are present.
2. If the tree shows only a few stems and limbs with 2 to 4 ft of dieback, wait for confirmation of laurel wilt before removing the tree. You can remove the dead part of the limb by cutting several feet below the dead area of the limb; burn or bury the infested limb.