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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.
Update on SOD:10-one liter water samples were collected from irrigation ponds at five increased risk nurseries. The 100 ml aliquots (roughly 10 per 1L sample) were filtered through a membrane and plated on PARPH-V8 agar media selective for Phytophthora spp. Suspect colonies were sub-cultured by hyphal tip transfer to fresh plates and observed over a thirty day period for characteristic coralloid hyphae and chlamydospores. No suspect P. ramorum cultures were obtained from any of the samples. This project was conducted cooperatively with the Ohio State University Plant and Pest Diagnostic Clinic with 2010 Farm Bill funds.