Two of the most important invasive Phytophthora
pathways into California wildlands
Commercial Nursery
Landscape to Wildland
1
Restoration Nursery
Restored Wildlands
Commercial Nursery
Restoration Nursery
2
Concern because new species of Phytophthora in
California restoration nurseries and now found in
restored wildlands
• Phytophthora tentaculata
• Described in Germany in 1993 from Chrysanthemums and other commercial
nursery plants
• First IDed in North America in 2012 in Monterrey Co., California Nursery
• Kills the California native Diplacus (syn. Mimulus) aurantiacus –
• symptoms typical of other root rotting Phytophthora species
• Symptoms: root and stem rot, with the roots and stem collars developing
necrotic, sunken lesions and few feeder roots, stunting, leaf russeting, and
chlorosis, defoliation and dieback of twigs, brown to black lesions girdling the
basal stem, and eventually plant death
• Been identified from nurseries in Butte, Alameda, Placer and Santa Cruz Counties
• Been recovered from restoration sites in Alameda Co.
Close evaluation of restoration sites and nurseries has
found many different Phytophthora species from many
different plant species
Plant species
Restoration county
Symptoms
Phytophthora species
Heteromeles
arbutifolia
San Francisco
root rot, root collar canker, foliage
discoloration (chlorosis), death
P. rosacearum, P. cryptogea, P. cactorum,
P. inundata, P. gonapodyides
Frangula californica
Marin
main stem dieback with resprout,
chlorosis, root rot, top dieback
P. cryptogea, P. multivora
Ceanothus
thyrsiflorus
San Francisco
stem and branch dieback, wilting,
root-rot, death
P. cryptogea, P. cactorum, P. multivora
Eriophyllum
staechadifolium
Marin, San Francisco,
San Mateo
root rot, dieback, and death
P. cryptogea, Phytophthora "megasperma like", P. crassamura, P. gonapodyides
Baccharis pilularis
Marin
chlorosis, stem necrosis, death
Phytophthora "cryptogea -like", P.
cryptogea, P. inundata
Artemisia californica Marin
stem and foliar dieback, necrosis
Phytophthora "cryptogea-like"
Stuckenia pectinata
San Francisco
necrotic spotting on seed collected
Phytophthora gonapodyides, P. crassamura
from pond water
Lupinus arboreus
Marin
Necrosis, foliage dieback, wilting
Phytophthora cryptogea
Evaluation of toyon field symptoms, plants
infected with P. cryptogea
root rot
root collar canker
Phytophthora cryptogea from diseased restoration H. arbutifolia plants
Frangula californica
infected with
Phytophthora multivora
No obvious symptoms
Phytophthora root rot
Phytophthora cactorum and Ceanothus thyrsiflorus
• Ceanothous root rot caused by Phytophthora species, especially Phytophthora
cactorum
• Symptoms: Root rot, dieback, branch dieback, and death
Photos by: Lew Stringer dieback of Ceanothus thyrsiflorus, associated with Phytophthora cryptogea, which was
isolated in the field from plants with these types of symptoms -Although in this case not from these particular
plants
Site with planted Eriophyllum st., and Ceanothus thrys., both
associated with P. cryptogea, also remnant Ceanothus thrys. downhill
from planting area was positive for P. cryptogea, plants were dying,
dead, or had dieback.
Photo by: Lew Stringer of
the Presidio Trust
Frangula california dieback associated with P.
multivora
Photos by Alison Forestel of NPS
With many different Phytophthora species, involved comes
differing levels of pathogenicity. Isolate species, and then
evaluate which species are responsible for disease observed.
How to keep Phytophthora out of wildlands...
Nurseries: Integrated approach of sanitation,
water management, monitoring, and host
selection
• Start clean –stay clean
• Pathogen free: benches, soil (and other planting media components)
containers, and plant propagules -leads to pathogen free plants for
landscapes
• group plants on benches based on their watering needs –water appropriately
using tensiometers if necessary
• monitor plants for symptoms weekly
• select plants that are not hosts
Land managers: Prevention first!
Prevention:
• Purchase clean materials
• Have sites tested first –if Phytophthora is present avoid host species
Cultural control:
• Good drainage
• No sprinklers watering trunks of trees
• Correct drainage
Chemical control:
• Several fungicides such as Aliette, Alude, Fosphite, Mefenoxam or Subdue may be
effective if not phytotoxic to the plants.
• Fungicides combined with cultural controls work better than either alone
Goldspotted Oak Borer
Native to AZ and Mexico
Introduced on firewood
1st detected in CA in 2004
• San Diego Co survey traps
Linked to tree mortality in 2008
Tens of thousands of coast live oak, CA black oak,
and canyon live oak trees killed
gsob.org
California Distribution
Risk
Sea level to
6,000 feet
Prepupae cold
tolerance of
about -0.4° F
Study - Cost of GSOB Remediation
Greater San Diego County RCD Project:
Removal of Dead Oaks in Descanso
 Tree removals
• 12-60 in
diameter
• Avg height 40 ft
 Approximate cost
• $9,000 per
parcel
• $1,200 per acre
• $1,500 per oak
Oaks Removed
Parcel Acreage
house present
no house
Total
<1
218
125
343
1 to 5
358
127
485
>5
391
113
504
967
365
1332
Slide courtesy of Tom Scott, UCR
 GSOB mitigation costs to date:
~$16 M
 Possible financial impacts if
GSOB becomes established in
more populated location?
Slide courtesy of Tom Scott, UCR
Remediation/Removal Costs for
Communities with Oaks
Oak density
Oaks
per
acre
Oaks
per sq
mile
Street Trees
0.50
320
Yard Trees
4
2,560
Cost/mile sq
Pasadena (23 sq mi)
low
medium
high
low
medium
high
240,000
480,000
1,600,000
5,520,000
11,040,000
36,800,000
1,920,000
3,840,000
12,800,000
44,160,000
88,320,000
294,400,000
Property Value Losses Associated with Loss of Oaks
Oak density
acre
Street
Trees
Yard
Trees
0.5
4
sq mile
Cost/mile sq
Pasadena (23 sq mi)
Low
$5K
Medium
$10K
High $30K
low
medium
high
1.6
million
3.2
million
9.6
million
36
million
73
million
220
million
13
million
26
million
77
million
294
million
588
million
1.8
billion
320
2,560
Slide courtesy of Tom Scott, UCR
Polyphagous & Kuroshio Shot Hole Borers
Female PSHB. A. Eskalen, UC Riverside
Invasive Beetle/Disease Complex
Polyphagous shot hole borer (PSHB)




• LA, Orange, Riverside, San Bernardino, and Ventura Counties
• 3 fungal species
Kuroshio shot hole borer (KSHB)
• San Diego and Orange Counties
• Closely related to PSHB
• 2 fungal species
Beetle – farmer
Affects seemingly healthy trees
Beetle/fungus affect vascular tissue
Internal symptoms on coast live oak.
A. Eskalen, UC Riverside
Hosts
More than 200 known hosts
Common urban landscape trees and agriculturally important
species
• Avocado, olive, persimmon
At least 35 reproductive hosts
• 13 native CA species
Dead box elder tree, Ontario, CA. A. Eskalen, UC Riverside
Distribution of Infestation
2012
2013
2014
2015
http://eskalenlab.ucr.edu/distribution.html
A. Eskalen, UCR
Tijuana River Valley
Regional Park
KSHB infestation December 9 2015 in southwestern San Diego County. Kevin Turner – UC Riverside (kevint@ucr.edu)
Photo point December 9, 2015 – willows dead, brittle, tops snapping off and falling into the water channel. Note that arundo is
the living green plant in the background. Flooding is a concern with so much dead wood falling into the waterway, especially
anticipating El Nino.