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Home , Corylus cornuta, Kalmia latifolia, Phytophthora ramorum, Pieris (plant)

PhytophthoraPhytophthora ramorum a guide for nurseries Edited 5.25.04 by A. Dailey, OSU, to include WSNLA changes per M. Toohey, and further revised 6.04.04 by J. Parke, R. Linderman and Figure 1. J. Pscheidt Ramorum diebak and newly described fungus-like retail outlet in Washington that was affiliated blight on organism named ramorum was with the Clackamas nursery. In a separate x discovered in 1993 to cause leaf blight, stem incident, in June 2003, infected bodnantense canker, and tip dieback on nursery-grown shipped from were found in two ‘Dawn’. and in Jackson County, , nurseries; they were aand the Netherlands. At about the same time, destroyed. The same California nursery also many tanoaks (Lithocarpus densiflorus) and had shipped camellias to two Portland-area (Quercus sp.) in the San Francisco Bay Area garden centers. Approximately 300 of these were dying from a new disease. The cause of were sold during January to July 2003. A this “sudden death” was also Phytophthora public recall was initiated in summer 2003 to ramorum. check plants and to remove and replace any infected plants found. In 2001, the disease was detected in sites near Brookings, in southwest Oregon, on Further state and federal regulatory actions tanoak, Pacific , and evergreen have been implemented to help prevent huckleberry. A nine-square-mile area was importing infected nursery stock; for more quarantined, and infected material was information, visit the Oregon Department of cut, piled, and burned in an attempt to Agriculture Web site at http://oda.state.or.us/ eradicate the disease. A few new infested forest plant/ppd/path/SOD/index.html. Pacific sites have been detected since then, so the Northwest nursery growers need to be alert for quarantined area has been increased slightly to inadvertent introductions of this , 11.5-square-miles. especially when importing from areas with known infestations or insufficient survey In May 2003, P. ramorum was discovered in a coverage. wholesale nursery in Clackamas County, Oregon, on , Viburnum, and Rhododen- Jennifer Parke1 and Jay Pscheidt1, and Robert Linderman2 dron. In June 2003, P. ramorum blight was 1Dept. of Botany and , Oregon State reported on rhododendron and other hosts at a University; Robert Linderman and 2USDA-ARS June 2004 Horticultural Crops Research Laboratory, Corvallis, OR. An up-to-date list of and associated is online at http://www. aphis.usda.gov/ ppq/ispm/sod/ list.pdf

Hosts Laboratory tests indicate that many more plant species, both wild and cultivated, are potentially In the , the host list is growing; Figure 2. Initial susceptible to P. ramorum. In , nursery as of this writing, it includes 29 hosts (Table symptoms of hosts include rhododendron , Viburnum ramorum leaf 2) and 31 associated species (Table 3) from spp., Pieris spp., Hamamelis virginiana, and blight on Vibur- many plant families. Associated species are spp. The disease has been reported num plicatum var. those found infected under natural condi- from nurseries and gardens in Germany, the tomentosum tions, and from which the pathogen has been ‘Mariesii’, showing Netherlands, Belgium, France, Poland, Spain, detected and/or cultured, but experimental Italy, Sweden, and the U.K. P. ramorum also has necrotic leaf spots confirmation of disease causality has not been and shoot dieback. been detected in a park on mature red oak demonstrated or documented. For an up-to- specimen trees ( and Q. falcata) date list of hosts and associated species, see and on (), http://www.aphis.usda.gov/ppq/ispm/sod/ (Aesculus hippocastanum), and seedlings of holm usdasodlist.html oak (Quercus ilex) in U.K. .

Table 1. Nursery hosts reported in the Pacific Northwest, plant part infected, and known symptions of . Plant Species Common Name Symptoms Japanese camellia Leaf lesions Camellia sasanqua Sasanqua camellia Leaf lesions latifolia mountain laurel Leaf lesions, shoot dieback x japonica Pieris x ‘Brouwer’s Beauty’ Leaf lesions, shoot dieback x japonica Pieris x ‘Forest Flame’ Leaf lesions, shoot dieback Japanese pieris Leaf lesions, shoot dieback Rhododendron hybrids rhododendron Leaf lesions, shoot dieback; death of mature plants Viburnum x bodnantense Bodnant viburnum Stem lesions Viburnum plicatum doublefile viburnum Leaf lesions, shoot dieback; var. tomentosum death of mature plants Viburnum tinus viburnum Leaf lesions, shoot dieback 2 Symptoms Phytophthora ramorum causes different symptoms on different hosts. “Sudden oak death” on tree species is characterized by “bleeding” cankers that girdle the trunks of tanoaks (Figure x) and some other oak species. On Rhododendron, Pieris, Vibur- num, Camellia, and evergreen huckleberry, the disease is characterized by leaf blight and shoot dieback and is more appropri- ately called Phytophthora ramorum blight. Symptoms on rhododendron may be indistinguishable from those caused by other Phytophthora species. The leaf petiole and midrib may be discolored, or the leaf tip or entire leaf blade may be necrotic. Leaf spots can occur where water accumu- lates on the leaf margins. die back when disease is severe. On Viburnum, infected may die and fall off, leaving dark, leafless stems. In more severe infec- tions, Viburnum can be killed. On Pieris, infected leaves turn a dark brown. Young shoots and leaves of Pieris are very suscep- tible to . Other hosts such as camellia may be infected but have only subtle symptoms, such as small leaf lesions on the lower leaves. Infected leaves on these themselves can also detach, germinate, and hosts often fall off. infect. Sporangia and zoospores can be moved Figure 3 (above). with windborne , in water, or with Viburnum Biology water splashed onto foliage. plicatum var. tomentosum Phytophthora ramorum is a fungus-like ‘Mariesii’ infected organism well adapted to the cool, wet P. ramorum produces chlamydospores, which in with P. ramorum, other Phytophthora species are important for conditions of the Pacific Northwest and at showing a necrotic the same time tolerant of heat and drought. surviving unfavorable conditions. There are two leaf as well as Unlike most Phytophthora species that infect mating types, designated A1 and A2. The forest defoliation near roots, P. ramorum is mainly a foliar patho- isolates from California and Oregon the base of the gen. It produces several types, are the A2 mating type, while plant. which helps the organism the European isolates survive and spread. are mainly A1. Figure 4 (at left). landing on Both mating Sporangia wet leaves or types have (clear) and stems germinate been isolated chlamydospores and infect the from (amber) of P. plant. Young Oregon ramorum on an leaves are and infected Oregon especially Washing- myrtlewood leaf. susceptible. ton Within a few nurseries. days, sporangia If both are produced, and mating types they release tiny, are in an infected swimming spores plant, the pathogen (zoospores). The sporangia could undergo sexual 3 Figure 5 (near right). Symptoms on Camellia include leaf lesions and defoliation.

Figure 6 (far right). Leaf spots on Camellia japonica caused by P. ramorum.

Table 2. Host plants for Phytophthera ramorum.

Plant species Common name bigleaf maple California buckeye menziesii madrone Arctostaphylos manzanita manzanita Camellia japonica Japanese camellia Camellia sasanqua Sasanqua camellia Hamamelis virginiana witch arbutifolia toyon Lithocarpus densiflorus tanoak Lonicera hispidula California Pieris formosa Himilaya pieris Pieris formosa x japonica pieris ‘Forest Flame’ Pieris floribunda x japonica pieris ‘Brouwer’s Beauty’ Pieris japonica Japanese pieris Pseudotsuga menziesii var. menziesii Douglas-fir coast live oak Quercus chrysolepis canyon live oak California black oak var. shrevei Shreve oak Rhamnus californica California coffeeberry Rhododendron rhododendron (including ) Rosa gymnocarpa wood coast redwood Trientalis latifolia western starflower californica Oregon myrtlewood, California bay laurel Vaccinium ovatum evergreen huckleberry Viburnum x bodnantense Bodnant viburnum Viburnum plicatum var. tomentosum doublefile viburnum Viburnum tinus laurustinus reproduction and form oospores. So far, Cultural management oospores of P. ramorum have been observed Familiarize yourself and your staff with the only under laboratory conditions, so their range of symptoms caused by Phytophthora role in disease is not known. In ramorum. Check your plants often. Diseases other Phytophthora species, oospores are also caused by other Phytophthora species can thick-walled, like chlamydospores, and are cause similar symptoms. If you suspect P. important for surviving unfavorable condi- ramorum, call the Washington Department of tions. Agriculture’s Pest Hotline at 1-800-443-6684 or email them at [email protected]. Disease prevention Diagnosis, using several techniques, may take Management efforts in Pacific Northwest 2 to 3 weeks. nurseries are focused on eradicating the pathogen where it is found and preventing While waiting for the diagnosis, do not move new . Early detection is vital to or ship symptomatic plants or any nearby preventing disease spread. Practices useful in plants; even if they look healthy, they may be managing other foliar Phytophthora diseases contaminated. also should help protect plants from infec- tion by P. ramorum. The following strategies Be alert for symptoms on any and tree can reduce the risk of this disease in PNW species, not just those on the list of hosts and nurseries. plant species associated with P. ramorum. Disinfect tools and shoes that may have been Exclusion and avoidance in contact with contaminated plants or If importing any species of trees, woody potting media. Incinerate contaminated pots vines or from any source (out of and trays or treat them with aerated steam to state or international), you must notify the kill the pathogen. Nursery Inspection Program Supervisor, Plant Protection Division at the Washing- Propagate cuttings only from plants known ton Department of Agriculture by fax at to have been free of disease for several (360) 902-2094 or email: months. Sanitize cuttings to eliminate the [email protected]. For more information pathogen; soak cuttings in a disinfectant Figure 7. Leaf on Washington’s import regulations, go to before storage and/or sticking in rooting and stem necrosis http://agr.wa.gov/PlantsInsects, and click medium. Use clean, pathogen-free potting and shoot on “Plant Diseases” or “sudden oak death”. media and clean, new pots. dieback on Pieris Federal USDA quarantine regulations japonica. regarding P. ramorum are online at http:// www.aphis.usda.gov/ppq/ispm/sod.

Keep imported known hosts and plants associated with P. ramorum in separate block at least 7 feet from other plants in the nursery for 3 to 6 months. This will allow you to see symptoms develop that initially might have been masked by or delayed by weather condi- tions.

If you visit infested areas, wash your vehicle and shoes before traveling to disease-free areas.

5 Manage irrigation to reduce the length of time that Protection and suppression foliage is wet. If possible, increase watering inter vals. Improve drainage to avoid puddling and with fungicides splashing. Place pots on fast-draining surfaces. Use fungicides as preventive treatments on known host plant species. Most Use only clean water for irrigation. Treat irrigation fungicides used to manage Phytophthora water to kill spores of P. ramorum and other do not kill this organism. They can only Phytophthora species. Remove and destroy any prevent the organism from becoming fallen leaf material, dead branches, or plants. established. They also can prevent continued growth if the organism is already inside the plant—thereby mask- ing symptoms that might have developed. Once chemical activity has subsided with time (about 3 to 6 months), the organism can resume growth within infected plants. This is why plants from other nurseries must be held for several months to see Table 3. Plant species associated with P. ramorum. whether symptoms become evident.

Plant species Common name If you choose to use fungicides, alternate among ones from different Abies grandis grand fir families with different modes of action. Aesculus hippocastanum horse chestnut For specific fungicides, consult the PNW Arbutus unedo strawberry tree Plant Disease Management Handbook or Camellia reticulata camellia An Online Guide to Plant Disease Control Camellia x. williamsii camellia at http://plant-disease.ippc.orst.edu/ sweet chestnut index.cfm. Corylus cornuta California Fagus sylvatica beech Kalmia latifolia mountain laurel Leucothoe fontanesiana drooping leucothoe Detection and Eradication Pieris formosa var. forestii Chinese pieris If P. ramorum is found in your nursery, Pieris formosa var. forestii x. P. jaonica pieris hybrid WSDA and USDA will work with you to Pittosporum undulatum Victorian box prevent further disease spread, eradicate Pyracantha koidzumii Formosa firethorn the infestation, and to monitor your Quercus cerris European oak nursery to verify when it is free from P. Quercus falcata southern red oak ramorum. The USDA is drafting uniform Quercus ilex holm oak procedures for dealing with nursery Quercus rubra northern red oak infestations. Check the final regulatory Rhamnus purshiana cascara action plan posted on the USDA-APHIS Rubus spectabilis salmonberry Web site for up-to-date information. The lilac action plan may include many of the Taxus baccata European yew following provisions. Toxicodendron diversiloba Poison-oak Vaccinium vitis-idaea lingonberry Samples will be removed from symp- Viburnum davidii David viburnum tomatic plants to confirm the identity Viburnum farreri (=V. fragrans) fragnant viburnum of the pathogen. Testing usually will be Viburnum lantana wayfaringtree viburnum part of the annual survey. Viburnum opulus European cranberrybush viburnum Samples will be taken from other plants Viburnum x. burkwoodii Burkwood viburnum in the nursery to determine the extent Viburnum carlcephalum x. V. utile viburnum hybrid of the infestation. Viburnum x. pragense Prague viburnum

6 Host plants will not be sold or moved during the investigation.

Blocks of plants containing infested plants will be destroyed by deep burial or incineration under USDA’s or WSDA’s direct supervision.

Healthy host plants within 10 meters of infested blocks will be held for 90 days* to observe symptoms.

Nonhost plants can be shipped during this time.

Surrounding properties will be surveyed for P. ramorum.

Trace-back investigations will be conducted to determine the source of infected plants, and trace-forward investigations will be conducted if any plants from the infested block(s) were shipped. Figure 8 (above left). Foliar WSDA will monitor water, potting symptoms on mix, soil, and plants for the presence susceptible oaks of P. ramorum. include a darkened petiole The nursery will be tested each year and midrib, as on for the next 2 years as a precaution. this tanoak leaf, or necrosis at the leaf base. For further information Davidson, J.M., Werres, S., Garbelotto, M., and updates Hansen, E., and Rizzo, D.M. 2003. Figure 9. (above right). Bleed- Oregon State University Extension Service. Sudden Oak Death and associated diseases ing canker on the An Online Guide to Plant Disease Control caused by Phytophthora ramorum. Plant trunk of a mature http://plant-disease.ippc.orst.edu/index.cfm Health Progress, Plant Management Network International. tanoak. Pscheidt, J.W. and C.M. Ocamb, eds. Pacific http://ww.plantmanagementnetwork.org/ Northwest Plant Disease Management pub/php/diagnosticguide/2003/sod/ Handbook (revised annually). Corvallis, OR: Extension Services of Oregon State Univer- Oregon Department of Agriculture, Sudden sity, University of , and Washington Oak Death Alert State University. http://oda.state.or.us/plant/ppd/path/ SOD/index.html Washington Department of Agriculture http://agr.wa.gov/PlantsInsects/ (see Plant USDA Animal and Plant Health Inspection Diseases or Sudden Oak Death) Service (APHIS), Pest Detection and Management Programs, Invasive Species California Oak Mortality Task Force and Pest Management: Sudden Oak Death http://suddenoakdeath.org/ http://www.aphis.usda.gov/ppq/ispm/sod/

* The 90-day period must be during active plant and pathogen growth; otherwise, the waiting period may be extended. 7 Acknowledgments The Washington State Nursery & Landscape Association gratefully acknowledges the authors of this publication, Oregon State University and the Washington State Depart- ment of Agriculture for technical assistance and financial support in revising and printing this publication for distribution to nurseries throughout Washington State. WSNLA is a trade association representing all Figure 10 (above facets of the nursery left). Rhododen- and landscape dron ‘Unique’ industry. plants with ramorum leaf blight. Plant in center foreground Photos Figure 1, Jan Hedberg, ODA; Figures was killed by 5 and 6, Cheryl Blomquist, California Depart- ramorum leaf ment of Food and Agriculture; Figure 7, blight; plant in Nancy Osterbauer, ODA; Figures 9 and 12, background shows Everett Hansen, Oregon State Uiveristy. All early symptoms of other figures by Jennifer Parke. ramorum leaf blight on lower leaves.

Figure 11 (above right). Lesions on leaf margins of Rhododendrons ‘Unique’. C 2003 Oregon State University. Produced and distributed in furtherance of the Acts of Congress of May 8 Figure 12 (at right, and June 30, 1914. Extension work is a cooperative program of Oregon State University Extension Service below). offers educational programs, activities, and materials - without discrimination based on race, color, religion, Ramorum shoot sex, sexual orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era dieback on wild veteran status. Oregon State University Extension Service is an Equal Opportuntity Employer. rhododendron. Published June 2004