Sudden Oak Death (Phytophthora ramorum)
Sudden Oak Death (Phytophthora ramorum) is caused by a recently described exotic species of Phytophthora isolated
from tanoak (Lithocarpus densiflorus) and red oak (Quercus spp.) located in a variety of forest types in central
California to southern Oregon. The pathogen is an oomycete water mold that causes canker, leaf blight, and die-back
diseases on a wide variety of trees and ornamental plants (Plant Dis. March, 2002). A minimum of 23 species in 12
families, notably the Fagaceae (Quercus sp.), Ericaceae (Kalmia sp., Pieris sp., Rhododendron sp., Vaccinium sp.),
Caprifoliaceae (Viburnum sp., Lonicera sp.), Aceraceae (Acer sp.), Pinaceae (Pseudotsuga sp.), Rhamnaceae (Rhamnus sp.),
and Theaceae (Camellia sp.) have been found naturally infected (Plant Health Progress. July 7, 2003). Symptoms of P.
ramorum include stem cankers that seep dark red sap on Quercus sp., stem and branch cankers, foliar lesions and dieback
on Rhododendron sp., stem lesions and wilting on Viburnum sp., and foliar lesions on Lonicera and Kalmia sp.
(Plant Health Progress. 2003), while no below-soil symptoms have been observed (Plant Dis. March, 2002).
Infestations in nurseries may be introduced by the movement of infected plant material from one nursery to
another, natural environmental movement of spores, or introduction of infested soil, water, or equipment.
P. ramorum has been recovered from rainwater collected around diseased trees indicating it can be moved by rain
splash or wind-driven rain (Plant Dis. March 2002), which could potentially be a source of spread within a nursery.
In 2004 the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS)
confirmed the presence of P. ramorum on nursery stock in 171 nurseries and retail garden centers in 20
states in the U.S and has since regulated movement of all commercially produced plant material originating
from California, Oregon and Washington.
In 2004 Ohio's greenhouse/nursery/Christmas tree industry generated more than $615 million so this pathogen has
the potential to significantly impact the state's economy if it is introduced. It is essential to conduct nursery
inspections in Ohio and take immediate steps to survey, detect the pathogen and take measures to prevent spread of
P. ramorum from western states where the pathogen is well established to locations in Ohio.
In 2005 1120 samples were collected from 28 high risk nurseries and in 2006 840 samples were collected from
21 high risk nurseries as part of the national SOD survey. No positive detections were made in Ohio. In 2007
and 2008 drastically scaled back surveys were performed as part of the CAPS program. In 2007 104 samples
from 21 nurseries and in 2008 131 samples from 26 nurseries were collected. Again no positive detections
were made in Ohio.
Symptoms of P. ramorum on non-oak hosts are highly variable. Suspect samples can be initially screened
for Phytophthora with a serological test (ELISA) but confirmation of the presence of P. ramorum requires
a nested polymerase chain reaction (PCR) test. If you suspect you have P. ramorum in your home landscape
or nursery operation contact the Ohio Department of Agriculture
Plant Pest Control Section.
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