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   Phytophthora cinnamomi (oomycete)
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    Details of this species in California
    Status: Alien
    Invasiveness: Invasive
    Occurrence: Reported
    Source: Menge, 1998
    Arrival Date: 1942
    Species Notes for this Location:
    Phytophthora cinnamomi was first isolated in California in 1942 but it has not previously been reported to caused significant mortality in natural stands of California native species (see impacts below) (Swiecki and Bernhardt 2003).

    P. cinnamomi is the cause of avocado root rot, the main limiting factor in avocado production, in California.

    Management Notes for this Location:
    Integrated management of avocado root rot includes planting clean avocado nursery stock, selecting low hazard sites, planting on mounds in more hazardous sites, preventing the introduction of P. cinnamomi, using resistant rootstocks, preventing over- or under-irrigation, applying systemic chemicals, treating with gypsum and adding organic mulches. It appears that avocados can survive and grow in the presence of P. cinnamomi if this management scheme is practiced.
    Location Notes:
    Economic/Livelihoods: Phytophthora cinnamomi is the cause of avocado root rot, the main limiting factor in avocado production. In California, it affects between 60 and 75% of orchards, and in 1989 caused an annual loss of approximately $44 million.
    Pathogenic: During an intense survey of natural woodlands around Lake Hodges (33°N, 117°W) in June 2001, symptoms typical of root and collar rot caused by Phytophthora spp. were observed on 27% of 474 coast live oaks (Quercus agrifolia) and on none of 86 Engelmann oaks (Q. engelmannii), in spite of intermixing of the two species. Symptoms on coast live oaks included viscous exudates emerging through intact bark matched by underbark dark lesions with irregular margins. Lesions were delineated by a dark line and present on the root collar or the buttress of symptomatic trees. Crowns of trees with lesions ranged from completely healthy to declining or dead. All symptomatic trees were in proximity of the lake or streams. P. cinnamomi was isolated and identified from trees in three distinct sites. Although Q. agrifolia is a known host for P. cinnamomi in California, this is the first report of widespread infestation of P. cinnamomi in natural oak woodlands in the western United States. Survey and inoculation results indicated Q. engelmannii to be less susceptible to infection. Inoculation results confirm previous research that cold temperatures are unfavorable to this pathogen and isolates differed in pathogenicity toward Q. agrifolia. Decline of oaks infected by P. cinnamomi was observed only in conjunction with other factors, in particular with the presence of the oak twig girdler, Agrilus angelicus Horn., an insect favored by stress conditions such as drought. Similar effects have been reported for Mediterranean oaks infected by the same pathogen (Garbelotto, Hüberli and Shaw 2006).
    Last Modified: 5/08/2005 8:47:30 a.m.

ISSG Landcare Research NBII IUCN University of Auckland