Oral Presentation Science Protecting Plant Health 2017

Fusarium dieback in California and other ambrosia beetle associated diseases of avocado and urban forest (4549)

Akif Eskalen 1 , S C Lynch 1 2 , J S Mayorquin 1 , J D Carrillo 1 , P Rugman-Jones 3 , R Stouthamer 3 , T Thibault 4
  1. Department of Plant Pathology and Microbiology, University of California Riverside, CA
  2. Department of Environmental Studies, University of California Santa Cruz, CA
  3. Department of Entomology, University of California Riverside, CA
  4. Huntington Library , Art Collections and Botanical Gardens, CA

Polyphagous shot hole borer (Euwallacea nr. fornicatus) an invasive ambrosia beetles that form symbioses with multiple fungal species, Fusarium euwallaceae, Graphium euwallaceae, and Paracremonium pembeum which together cause a disease called Fusarium Dieback (FD) on trees in urban and native forests in California. Females are black colored and about (1.8 – 2.5) mm long; males are brown colored and about 1.5 mm long. In California, PSHB was first reported on black locust in 2003 but there were no records of fungal damage until 2012, when the F.euwallaceae was recovered from the several backyard avocado trees infested with PSHB in Los Angeles County. The aim of this study was to determine the plant host range of the beetle-fungus in two heavily infested botanical gardens in Los Agneles County. Off the 335 tree species observed, 207 (62%), representing 58 plant families, showed signs and symptoms consistent with the attack by PSHB. The F.euwallaceae was recovered from 54% of the plant species attacked by PSHB, indicated by the presence of the F.euwallaceae at least at the site of the entry hole. Trees attacked by PSHB included 11 species of California natives, 13 agriculturally important species and many common street trees. Survey results also revealed 19 tree species that function as reproductive hosts for PSHB. Since 2012, the number of reproductive hosts for PSHB has increased from 19 to 49, and includes 20 species that are native to California. The infestation has spread from a single county in 2012 to seven counties in 2017. Furthermore, the infestation was originally limited to the urban forest but it has recently spread into native forests in southern California.