| The species listed below have been featured as 'Host of the Month' in past issues of the COMTF Monthly
Report. (back to top)Abies concolor (white fir) This is an evergreen tree native to the mountains of southern Oregon, California, the southern Rocky Mountains, and Baja California. Large and symmetrical, white fir grows 80 – 120ft tall and 15 – 20ft wide in its native range and in the Pacific Northwest. White fir is one of the top timber species found in the Sierra Nevada Mountains of CA and is a
popular Christmas tree, as well as one of the most commonly grown native firs in Western gardens. Young trees are conical in shape, but develop a dome-like crown with age. The flattened needles of white fir are silvery blue-green, blunt at the tip, and grow 2 – 3in long. Often curving upwards, the needles
extend at right angles from the twig, and twigs produce a citrus smell when needles are broken. White fir is monoecious, producing yellow- to red-toned, catkin-like male flowers and inconspicuous yellow-brown female flowers. The oblong cones grow 3 – 5 ½in upright, are yellow-green to purple in color, and are deciduous at maturity, dispersing seed in the fall. New twigs are dark-orange, but become gray-green, then gray with maturity. The bark of saplings is thin, smooth, and gray, turning thick, ash-gray with age, and developing deep irregular furrows. P. ramorum- infected Abies concolor (white fir) was first reported in the
October 2005 COMTF newsletter as having been found at a Christmas tree farm in the quarantined county of Santa Clara. Additional sampling of the tree farm is underway. Koch's Postulates have not been completed. The USDA Animal and Plant Health Inspection Service (APHIS) has reviewed the CDFA data and expects to add A. concolor to the official list of associated host plants soon. References: - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. p 163.
- Virginia Tech Forestry Department; Dendrology at Virginia Tech; Abies concolor, 2005-2006
Acer davidii – David's maple (Aceraceae) – was named after the Jesuit priest, Jean Pierre Armand David, who discovered it in China in 1869. This deciduous tree, native to central China, Grows 20 – 35 ft. tall and wide, and has shiny green bark striped with silvery white. Leaves are
glossy green, lobed, have deep veins, and grow 2 – 7 inches long and 1.5 – 4 inches wide. New foliage has a bronze-tinted appearance, with fall colors revealed in yellow, red-orange, and purple. Spring flowers are clustered and greenish yellow, and the glabrous samara fruits are approximately 3 cm long and horizontally spread. David's maple was first identified on 11/25/05 in a Canadian nursery.
With Koch's postulates not yet completed, it will be added to the USDA APHIS associated host list. References: - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. p 167.
- Oregon State University, Department of Horticulture; Landscape Plants; Images, Identification, and Information, Vol. 1, 1999 - 2006 http://oregonstate.edu/dept/ldplants/acda.htm
(back to top) Acer laevigatum (Evergreen maple) This is a frost-sensitive tree native to the Himalayas and China, and can grow to 35 feet. Its leaves are lanceolate shaped and can grow five inches or more in length. Evergreen maple was detected in a United Kingdom outdoor green area. Symptoms included chlorotic leaves and leaf necrosis. References: Acer pseudoplatanus (Planetree Maple) This hardy tree is native to Europe and central Asia, and has been cultivated in Europe for centuries. While it prefers cool, sunny environments, it is generally very adaptable, and tolerates salt and
seaside locations. It is also a good shade tree for lawns. The Planetree Maple is easily transplanted and established, and has even demonstrated a capability of escaping from cultivation and naturalizing in minimally managed areas. Planetree Maple is a deciduous, medium to large tree, growing 40 ft. or
more in height and nearly as wide. Its foliage and branching is dense and compact, with upright spreading. Planetree Maple bark is irregularly scaly, and is a steel gray color with orange color showing when bark flakes off. Summer foliage is attractive, with thick, leathery leaves that are 3 – 6 inches across and have impressed veins and coarsely toothed margins. The leaf surface is dark green on the top and greenish white
on the underside. Autumn foliage is generally poor and yellowish to greenish brown. This tree blooms yellowish-green flowers in May and produces samaras 1.25 – 2 inches in pendulous clusters. This species is susceptible to necrotic cankers, aphids and sooty mold, stem borers, and twig dieback in cold winters. P. ramorum was found causing characteristic lesions on an infected
Planetree Maple found at a known P. ramorum-positive woodland garden site in the UK. The 70 cm diameter tree had lesions on two sides of the trunk, extending from ground level to 1.5 and 2.0 meters high. The pathogen was readily isolated from cankers. Additionally, Armillaria was identified on the tree as a secondary invader. References:
- Personal email communication
Clive Brasier, Emeritus Mycologist
Forest Research, UK Forestry Commission - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 169.
University of Connecticut - UConn Plant Database of Trees, Shrubs, and Vines
Acer pseudoplatanus
http://www.hort.uconn.edu/plants/a/acepse/acepse1.html
(back to top) Adiantum aleuticum (Maidenhair fern) This fern is native to western North America and thrives along shady
moist banks, streamsides, and in serpentine soils. It has reddish-brown to black petioles, and its fronds create an airy effect, forking to make a fingerlike pattern atop slender stems reaching 1-2 ½ feet tall. The stems of this Maidenhair fern are used for designs in basketry by the Karok, Makah, Quinault, Tolowa, and Yurok. This fern is most commonly planted in containers or shaded beds. Symptomatic P. ramorum maidenhair fern were found along the same Mendocino County tributary as infected V. planipetala and T. californica (see below). Symptomatic plants were found on a hillside associated with infected CA bay laurel, tanoak, Pacific yew, woodrose, CA honeysuckle, madrone, evergreen huckleberry, and toyon. Symptoms were similar to those observed on Adiantum jordanii (CA maidenhair fern)
, with necrotic areas on the leaves. The necrosis appeared to begin near the leaf margins and advance between the veins. Although some leaves were nearly or entirely necrotic, the disease did not appear to be fatal to the ferns. P. ramorum has been recovered from plated leaf tissue, but PCR testing has not been conducted. State and federal regulatory officials are reviewing the findings. References: (back to top) Adiantum jordanii (California maidenhair fern) Native to California and southern Oregon, this fern is found in shaded hillsides and in moist woody areas under oaks and pines or on damp banks at the base of rocks and trees. Fronds are twice-divided and
grow to 2ft. Maidenhair fern requires steady moisture and soil rich in organic matter. It is s close relative of Adiantum spp commonly sold as a houseplant and appreciated for its graceful form and delicate structure. The symptomatic maidenhair fern were found at Jack London State Park along a trail with symptomatic woodrose, western starflower, and CA
bay laurel. Symptoms on the ferns ranged from leaf spots to entirely necrotic leaves. References: (back to top) Arbutus unedo (Strawberry tree)Strawberry tree is native to southern Europe and Ireland and is a
common landscape tree in low-lying areas of the western United States that do not have severe winters. Since it is drought tolerant and attractive, it is commonly planted in the Bay Area. It is closely related to madrone (Arbutus menziesii), a native to the Pacific Coast of the United States and British Columbia, and also a host for Phytophthora ramorum. Strawberry trees are attractive and compact, with smooth, shredding reddish bark, and grow to about 35 feet in height. It has clusters of small white urn-shaped flowers in the fall and winter, and round fruits turning from yellow to red that take a year to ripen. It is tolerant of a wide range of moisture conditions, wind, and pollution. This spring (2003), Phytophthora ramorum was isolated from strawberry
trees and camellias in a garden center on the island of Majorca, Spain. Phytophthora ramorum-infected rhododendron and viburnum plants had been confirmed in this garden center prior to the new finds; consequently, it is believed that the camellia and strawberry trees were infected on-site. Symptoms of the disease on strawberry tree are similar to those on madrone, with leaf necrosis extending down the leaf,
through the petiole and into the twig. Strawberry tree leaves have been found to be highly susceptible to Phytophthora ramorum in laboratory tests. (Moralejo and Hernandez, 2002. Inoculation Trials of Phytophthora ramorum on Detached Mediterranean Sclerophyll Leaves. Sudden Oak Death Science Symposium, http://danr.ucop.edu/ihrmp/sodsymp/paper/paper25.html.) The susceptibility of strawberry tree is not only of concern to the nursery industry and gardeners in Europe and North America, but for the natural ecosystem of the Mediterranean, since this species occurs extensively in this area (Moralejo and Descals, 2003. Risk analysis of Phytophthora ramorum establishment in the Mediterranean area, Sudden Oak Death Online Symposium, http://www.apsnet.org/online/sod/Papers/Moralejo_Descals/default.htm.) Ardisia japonica (Japanese ardisia) Japanese Ardisia or marlberry (Myrsinaceae) – is native to Asia, and is one of two species in this genus typically grown in Western gardens. It is a low-growing non-aggressive evergreen shrub that spreads by
runners to produce upright branches ranging 6 – 18 inches high. Its leathery, 4-inch-long bright green leaves cluster at the tops of branches. Its pink and white star-shaped flowers, ranging from 2 – 6 in a cluster, appear in fall and are ½ inch in size. The bright red berries can be found throughout winter. This plant makes a good ground cover in the shade, but requires well-drained soil and does not tolerate foot traffic. Ardisia japonica was first found P. ramorum-positive on 12/14/05 in a Canadian nursery. Since Koch's postulates have not been completed, this species will be added to the USDA APHIS Associated Host List. References: Calcyanthus occidentalis (Spice bush) This deciduous shrub is native to California's Coast Ranges and Sierra Nevada foothills, growing along streams and moist slopes. It grows 4-12 ft. high and equally as wide. Its bright green leaves turn yellow in the fall, and range from 2-6 inches long and 1-2 inches wide. In mid- to late spring or summer, brownish red fragrant flowers up to 2 inches across
can be found. Spice bush requires regular watering and grows well in sun or shade. It is tolerant of sandy or clay soil, as well as poor-drainage and seasonal flooding. It can be trained into a spice vine or used as a multi-stemmed small tree, but is best as a background shrub or screen. Symptomatic spice bush samples from Jack London State Park were
found along a creek near symptomatic bigleaf maple and CA bay laurel. Symptoms on spice bush ranged from leaves with necrotic lesions along leaf margins to dead leaves. The lesions were grayish-brown in color, and some had a dark margin. Small necrotic spots were also observed beyond the lesions found on spice bush. (While this is the first official confirmation of spice bush, original identification was made by Arborist Rob Gross in Sonoma County.) References: - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. p 242.
- Las Pilitas Nursery
Calycanthus occidentalis
http://www.laspilitas.com/plants/127.htm - Personal email communication
Dave Rizzo, Professor
Department of Plant Pathology, UC Davis (back to top)
Calluna vulgaris (Scotch Heather) Added to the USDA APHIS associated host list in August, Calluna
vulgaris is native to much of Europe. It is a low-growing evergreen groundcover, growing 2 – 3' tall and equal in spread. Branching is upright, forming thick, compact, dense mats. The evergreen leaves range from .05" - .1" long, are scale-like, and are 4-ranked with opposite arrangement, making shoots look square-like. Foliage is medium green during the summer, turning bronze, yellow, reddish, or silvery in
autumn depending on the cultivar. Scotch Heather flowers range in color from rosy to purplish pink, and are .25" long and clustered. Infested Calluna vulgaris was identified in Polish container-ornamental nurseries. Symptoms were observed on plants near the nursery road, and included cankers on 2 – 4 cm shoots, as well as shepard crook tips. Koch's postulates have not been completed. Although this first report of P. ramorum in Poland on Calluna vulgaris nursery stock is preliminary, it does raise concern that heathlands in the
UK and other parts of Europe may be impacted by this pathogen. Heathlands composed of Calluna vulgaris, Vacciniums and other plants support many rare wildlife species and are ecological valuable. For more information on the heathlands and the importance of this natural resource, go to the European Heathlands homepage at: http://www.english-nature.org.uk/heathlands/default.htm. Cinnamomum camphora – camphor tree (Lauraceae) – is an evergreen tree native to China, Taiwan, and Japan. This slow-growing, strong-structured tree has a substantial trunk with heavy, upright spreading limbs, and grows to more than 50 ft. in height. Its leaves grow 2.5 – 5 in. long and are a glossy green with three main veins arriving from near the base. When crushed, the leaves produce an aromatic camphor smell. New foliage in early spring appears pink, red, or
bronze, maturing to a shiny yellow-green. Fragrant yellow flowers bloom in spring, followed by small blackish fruits. Camphor tree timber can be distilled to produce an essential oil. Traditional uses of camphor include colds, influenza, fever, pneumonia, inflammation, and diarrhea. However, camphor is toxic in large doses and
should not be used without professional supervision. P. ramorum-positive Cinnamomum camphora was found in the UK. Symptoms included shoot tip die-back and stem necrosis or canker. Consequently, USDA APHIS has added this species to the list of regulated Plants Associated with Phytophthora ramorum.
Resources: - Van Wyk, Ben-Erik and Wink, Michael. Medicinal Plants of the World. Portland, OR: Timber Press, Inc., 2004. 104.
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 275.
Clintonia andrewsiana (Andrew's clintonia bead lily/Andrew's clintonia/Red clintonia/blue-bead lily)Andrew's clintonia bead lily is closely associated with redwood forests, making their ranges very similar. While redwood forests with bead lily in the understory are found from San Luis Obispo County, along the Northern California coast, Andrew's clintonia bead lily is believed to have been extirpated from its former range in coastal southern Oregon. Andrew's clintonia bead lily grows in moist, shady forests at elevations
less than 2,000 feet. The plant is one of the larger species in the genus Clintonia, with a rosette of 5 to 6, 10 inch-long leaves and a central flower stalk up to 20 inches tall. Attractive, deep red bell-shaped flowers, which bloom from May to July, are followed by light blue berries. (See a photo of healthy Clintonia andrewsiana.)
Phytophthora ramorum-infected Andrew's clintonia bead lily was found at Muir Woods National Monument, Marin County, in March, 2004. The infected plants were under a canopy of redwoods and infected California bay laurel. Symptoms included lesions both at the tip and base of the leaves. Note that over time, the necrotic tissue develops a shot hole
appearance. (See photos of infected Clintonia andrewsiana.) Resources: Drimys winteri (Winter's-bark) Native to Argentina and Chile, Winter's-bark is an evergreen tree that can grow to a height of 50 ft. Its mildly fragrant flowers bloom from late winter to mid-spring, are white with yellow centers, and are found in
clusters on branch tips. Its leathery aromatic leaves have a peppery smell when crushed, and the aromatic bark is used to treat certain stomach ailments. Winter's-bark grows best in full sun to light shade, and prefers moderate temperatures in addition to well-drained soil. Phytophthora ramorum-infected Winter's-bark was found in Southwest England, December 2003. The plant was a large bush shape, and
exhibited foliar blight as well as shoot dieback. Numerous infected rhododendrons were also found in the vicinity. To date, Koch's postulates have not been completed, as the host was originally thought to be a rhododendron, so the isolate was discarded. Resource: (back to top)
Dryopteris arguta (California wood fern/coastal wood fern) California wood fern is a common understory species growing in moist, open wooded areas, especially along creeks and northern slopes. It
ranges from Arizona to British Columbia, at elevations up to 6,000 feet. Fronds are 1-2 feet in length, and 5-7 inches wide. (See a photo of healthy Dryopteris arguta.) CA wood fern root stocks were used by Native Americans as a starchy food source. Infected coastal wood fern was found at Fairfield Osborne Preserve in
Sonoma County, CA in a coast live oak/California bay laurel forest. Symptoms were necrotic frond tips. This host find is significant because previously identified P. ramorum hosts were limited to plants with seeds: Gymnosperms (Douglas-fir, redwood, yew, and grand fir) and a wide range of Angiosperms (broadleaf plants). This is the first known P. ramorum-susceptible species in the fern group (division Pteridophyta). Resource: (back to top) Euonymus kiautschovicus (Spreading euonymus) Euonymus kiautschovicus (E. patens) – Spreading Euonymus (Celastraceae) – is native to eastern and central China, and grows to 8 ft. tall and at least as wide. This shrub is often an evergreen, although it may lose leaves or suffer leaf damage if snow is present or temperatures reach 0° F. Its 2 – 3 in. dark-green, thin-textured leaves
are oblong shaped and grow in an opposite leaf arrangement. Small greenish white flowers can be found blooming in July and are attractive to bees. The characteristic squarish "hatbox" fruit matures in October and is pink with orange seeds. This durable shrub is often used for landscape structure, as a hedge or divider. Euonymus kiautschovicus was found P. ramorum-positive for the first
time on 12/8/05 in a Canadian nursery. With Koch's postulates not yet complete, it will be added to the USDA APHIS federal P. ramorum Associated Host List. References: (back to top) Fagus sylvatica (European beech)European beech's natural range extends across southern Scandinavia
down to central Spain, Corsica, Sicily, and Greece, as well as eastward to western Russia and Crimea. European beech is common and prized in the UK. Roughly one third of the UK's forestland is hardwood, comprised of beech oak, birch, and ash. The total area of forest and woodland in Britain is more than two million hectares, approximately 10% of the UK's total land area. Botanists are uncertain whether European beech naturally colonized the UK following the last Ice Age, or if it was introduced by humans, but the tree has an important place in the UK's culture and natural environment. Beech nuts were eaten by prehistoric man and are still consumed today. Beech wood has been used for centuries for both firewood and furniture.
Historians claim that the first written European literature was inscribed on beech bark in Sanskrit. The English word 'book" comes from the Anglo-Saxon "boc," a derivative for the Anglo-Saxon "beece" or beech. A wealth of information on European beech and other UK forest species may be found on the Royal Forestry Society website: http://www.rfs.org.uk/ In addition to growing in natural stands in Europe, European beech is widely planted as an ornamental tree in the US. European beech is a stately tree (see photo), and is more tolerant of cultivation and human disturbance than its North American counterpart, Fagus grandifolia. A
number of European beech cultivars have been developed, including `Asplenifolia' with finely cut foliage; `Atropunicea' with purple foliage; `Fastigiata' with a columnar form; and `Pendula' with weeping branches. To date, only two beech trees in Cornwall, England have been found with bark cankers and bleeding symptoms similar to those on true oaks
and tanoak in California. Inoculation studies indicate European beech is highly susceptible to P. ramorum (http://www.defra.gov.uk/planth/pra/sudd.pdf), but European beech's susceptibility in a natural setting is not yet fully understood. References:(back to top) Fraxinus latifolia (Oregon ash) This is a deciduous tree that thrives in moist conditions and is native to the West Coast of the US. It is most often
found in central oak woodlands, northern oak woodlands, riparian environments, and yellow pine forests. Growing 40 - 80 feet tall and one to three feet in diameter, this is one of only a few native western trees with compound leaves. These pinnately compound leaves are five to 14 inches long, have five to nine leaflets that are broadly ovate, obobate, or elliptical, and are green above and paler in color below. The Oregon ash flower is dioecious
, small, greenish-white in color, and borne in dense clusters. Its flat samaras are one to two inches long and are attached singly, but hang in clusters. The twigs of this tree are stout and round, with flattened nodes, and appear olive-gray when young, turning gray-brown with age. Its bark is thin, smooth, and gray-green when young, eventually thickening to 1 ½ inches and furrowed with thin, flat ridges and a gray-brown color. The wood of Oregon ash is used for making baseball bats
and ax handles. A P. ramorum-symptomatic Oregon ash was found at Sugarloaf State Ridge Park, along Sonoma Creek, near the visitor's center. The infected tree was part of a research plot established that included 10 P. ramorum infected CA bay laurel trees. Symptoms on the Oregon ash consisted of necrotic lesions developing on the leaves and along the leaf
margins. Lesions had a grayish-brown color with a water-soaked appearance, similar to lesions caused by ash anthracnose. Leaf tissue isolations were made, and P. ramorum was recovered. PCR testing has not been performed. State and federal regulatory officials are reviewing the findings. References: (back to top) Gaultheria shallon (Salal) Gaultheria shallon – Salal (Ericaceae) – is a member of the heather family and a common evergreen shrub native from California's central coast to British Columbia. Capable of reaching 4 – 10 ft. tall and slightly wider, in the unfavorable conditions of full sun and poor, dry soil, this plant only reaches 1-2 ft. high. Its nearly round, glossy, bright green
leathery leaves are 1 ¾ - 4 in. long, and finely serrated. The bell-shaped pendent white or pink flowers are found in 6 in.-long loose clusters and can be seen on reddish stalks in spring. The edible fruit of this plant follows the spring blossoms and appears black, resembling large huckleberries. Although the berries have a bland flavor, birds eat them. Salal is also useful as a groundcover in moist, shady, peaty soils,
and branches are also collected for use by florists in bouquets. The name shallon is a derivative of Kikwu-salu, the Chinook name for this plant. Salal was confirmed positive for P. ramorum on 12/20/05 in a Canadian nursery. Since Koch's postulates have not been completed, this species will be added to the USDA APHIS Associated Host List.
References: Griselinia littoralis (New Zealand Privet)
Girselinia littoralis – New Zealand Privet – is an evergreen shrub native to New Zealand. Flowering in May, the New Zealand Privet grows to 6 m high and nearly as wide. Having dioecious flowers, both male and female plants must be grown to produce seed. Tolerating maritime exposure,
this plant grows well by the sea and likes full or partial sun as well as moist soil. It has an upright form and thick, leathery, lustrous green leaves. Since this shrub always looks well groomed and has a dense, compact screen, it is a good shrub for espalier use and is often used as an ornamental. P. ramorum-infected New Zealand Privet was found on one established
plant in South Wales. Symptoms included leaf blight and dieback. Culturing and TaqMan PCR are complete; Koch's postulates are pending. The identified plant has been destroyed. Resources: - Plants for a Future, "Griselinia littoralis"
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 376.
(back to top) Hamamelis mollis (Chinese witch-hazel) Hamamelis mollis - Chinese witch-hazel – is a deciduous large shrub or
small tree native to central China. As a shrub, Chinese witch-hazel grows slowly to 10' - 15' tall and wide; as a small tree it may reach 30 ft. Its somewhat rounded leaves grow 3" – 6" long and are dark green and rough on the top side, while gray and felted underneath. Turning yellow to yellow-orange in the fall, the Chinese witch-hazel has very showy autumn foliage. Its flowers have a sweet fragrance and grow 1 ½" wide.
Blooming on bare winter stems, these rich golden yellow flowers with red-brown sepals are excellent for cutting. P. ramorum-infected Chinese witch-hazel was found on one grown plant in South Wales. Symptoms included leaf blight and dieback. Culturing and TaqMan PCR are complete, but Koch's postulates are not. The identified plant has been destroyed. Hamamelis mollis is the second P. ramorum-regulated witch hazel, following Hamamelis virginiana. Resources: - University of Connecticut, Plant Database, "Hamamelis Mollis"
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 379.
(back to top)
Hamamelis verginiana (witch hazel)Another Phytophthora ramorum host has been discovered in the United Kingdom, Virginian Wych hazel or witch-hazel (Hamamelis virginiana).
Witch-hazel is a deciduous shrub or small tree with a short trunk, bearing numerous spreading, crooked branches. At maturity, it is commonly 15 to 25 (4.5-7.5 m) feet tall. This is the first tree host to be identified in Europe. Witch-hazel is native to North America. The genus name (Hamamelis)
translates from Greek as "at the same time" and "apple," possibly because flowers and fruits are present simultaneously. The species name (virginiana) refers to the Virginia colony. It obtains its common name from the dowsers, or "water witches" who used forked witch-hazel sticks to detect groundwater. Leaf and bark extracts were traditionally used medicinally, a practice that is still common today. Extracts of the twigs
were also believed to infuse the imbiber with occult powers. Witch-hazel is unusual in its flowering schedule. Pale yellow flowers appear from late October to early December and are pollinated by the winter moth, which can visit trees during temperatures as low as 28º F. Because of this rare winter flowering and its tolerance for shade, witch
-hazel is a common ornamental tree. As individuals, witch-hazel probably does not live more than 100 years, but they reproduce from root sprouts, and clones may live for a very long time. The P. ramorum-infected witch-hazel was discovered in August 2003 in a public garden in Wales. The garden was being treated to eradicate P. ramorum from infected rhododendrons. The symptoms on witch-hazel
were brown lesions on the leaves, often delimited by large and small leaf veins, and often on the leaf tip or edge. Twigs were also affected, resulting in aerial dieback. Laboratory test confirmed P. ramorum and Koch's postulates were completed. The plants were destroyed and measures taken to eradicate P. ramorum. No other cases of infected witch-hazel have been found. References:- P.M. Giltrap, A.J. Inman, V.C. Barton, A.V. Barnes, C.R. Lane, K.J.D. Hughes, J. Tomlinson, M.L. Dean and K. Izzard. Plant Health Group, Central Science Laboratory (CSL), Department for Environment, Food & Rural Affairs; Plant Health and Seeds Inspectorate (PHSI); and Horticultural Marketing Inspectorate.
- U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (2003, October). Fire Effects Information System, [Online]. Available: http://www.fs.fed.us/database/feis/ [17 October 2003].
- Tree Guide, Athenic Systems – The Outdoor Asset Management
Company. http://www.treeguide.com/
(back to top) Hamamelis X intermedia (Hybrid witchhazel) Hamamelis X intermedia – hybrid witchhazel (Hamamelidaceae) – is a group of winter-blooming hybrid shrubs between H. mollis and H. japonica. These deciduous shrubs, with upright, loosely branched forms, grow 12-15 ft. high and wide and are often grafted. The bright fall foliage and yellow to red blooming clusters flower in winter, and appear
as narrow, crumpled petals, resembling shredded coconut. Hamamelis X intermedia was found P. ramorum-positive 7/6/05 in a Canadian nursery. Koch's postulates have not been completed, so this species will be added to the USDA APHIS Associated Host List. References: Laurus nobilis (Sweet bay laurel) Sweet bay laurel is an evergreen shrub or small tree, native to Mediterranean region woodlands. It can grow 12 – 15 ft. tall and equally as wide, or it can be clipped and shaped as a shrub. It is adaptable to sun or shade, and while it requires well-drained soil, it is drought tolerant
once established. The dark to bright green leaves are very fragrant, and after drying can be used for culinary flavoring. Leaves and branches are also used for garlands and wreaths. As a medicinal plant, bay leaves and berries have been used for rheumatism, skin rashes, earaches, and insect repellent. Phytophthora ramorum-infected Sweet bay laurel was identified in a
Southwest England nursery, May 2004. The infested plants were container grown and exhibited foliar blight symptoms. Other infected container-grown plants were also identified at the nursery. Koch's postulates have been completed. Once the UK reports its completed findings to APHIS, and APHIS reviews and accepts the information, Laurus nobilis will be moved from the associated host list to the host list. Resource: - Simon, J.E., A.F. Chadwick and L.E. Craker. 1984. Herbs: An Indexed Bibliography. 1971-1980. The Scientific Literature on Selected Herbs, and Aromatic and Medicinal Plants of the Temperate Zone. Archon Books, 770 pp., Hamden, CT.
(back to top) Leucothoe axillaris (Coast leucothoe) Coast Leucothoe (Ericaceae) - is a relative of Pieris and native to the
south-eastern US. A spreading, arching evergreen plant that grows 2-4 ft. tall and 3-6 ft. wide, its leathery, shiny leaves are 4 inches long and bronze upon emerging, turning dark-green once mature, and then red in winter. Its drooping urn-shaped creamy white flowers bloom in mid-spring along the stems and grow 1-3 inches long in clusters. Coast Leucothoe was confirmed P. ramorum-positive on 7/6/05 in a
Canadian nursery. Since Koch's postulates have not been completed, this species will be added to the USDA APHIS Associated Host List. References: - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA:
Sunset Publishing Corporation, 2001. p 430.
Magnolia stellata (Star magnolia) Magnolia stellata – star magnolia - is a deciduous shrub native to East
Asia/Japan. Growing 10 feet high and having up to a 20 foot spread, this slow growing shrub or small tree has large, scented white flowers that blossom before the plant leafs out. The flowers grow to 3" and are pollinated by beetles. The star magnolia requires well-drained, moist soil and can grow in semi-shade to full sun. A very ornamental plant, it is popular in borders or garden entries. P. ramorum-infected star magnolia was found on one established plant in South Wales. Symptoms were limited to leaf blight. Culturing and TaqMan PCR are complete; Koch's postulates are pending. The identified plant has been destroyed. Resources: - Plants for a Future, "Magnolia stellata"
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 453.
(back to top) Magnolia x loebneri (Loebner magnolia) Magnolia x loebneri – Loebner magnolia – is a deciduous slow growing hybrid of Magnolia kobus and Magnolia stellata. This shrub commonly grows 12' – 15' and is similar in spread. Loebner magnolia flowers are similar to that of Magnolia stellata, although somewhat longer and wider and fewer in number. Blooming occurs before leaf out in mid-spring, with some selections being fragrant. This shrub is commonly used in lawns as
a shrub border or as a woodland edge. Loebner magnolia was found infected with P. ramorum on one established plant in South Wales. Symptoms were limited to leaf blight. Culturing and TaqMan PCR are complete; Koch's postulates are pending. The identified plant has been destroyed. Resources: - Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 450.
(back to top) Magnolia x soulangeana (saucer magnolia) Magnolia x soulangeana – saucer magnolia – is a deciduous hybrid of
Magnolia denudate and Magnolia liliiflora. This small tree can grow to 30' with equal spread. It may be multi-trunked or have low main branches and is round to irregular in shape. Saucer magnolia leaves are 3" – 6" long and half as wide, and are elliptical in shape with a sharply pointed tip. New foliage is reddish bronze, turning dark green with age and yellow-brown in the fall. The fragrant flowers bloom in late winter or
early spring and are white to pink or purplish red, cup-like in shape, and range from 3" – 6" wide. Saucer magnolia prefers moist, fertile, deep soil and full sun. It is commonly used as a lawn plant and as an anchor plant in big container plantings. Saucer magnolia was found infected with P. ramorum on three grown
plants in a nursery in Northwest England. Symptoms included leaf blight and dieback. Culturing and TaqMan PCR are complete; Koch's postulates are pending. The identified plants have been destroyed. Resources: - University of Connecticut, Plant Database, "Magnolia x soulangeana"
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 452.
(back to top) Michelia doltsopa (Michelia) This
is an evergreen tree native to China. In its natural Himalayan environment, it can grow to 90 feet, but it has only been found to grow to 25 feet in the western US. This tree varies from bushy, to narrow and upright. Its leaves are thin-textured, dark-green, and leathery, growing three to eight inches long and one to three inches wide. In the winter, furry brown buds open to blossoms ranging from cream-colored to white,
with a slight green tinge at the base. The flowers are five to seven inches across, with 12 to 16 segments that each grow to an inch wide. During flowering, this tree may be mistaken for a magnolia. Surviving in zones 14 – 24, H1, H2, this tree requires regular watering and part shade in its hottest climate range. Michelia was detected in an outdoor green area of the United Kingdom.
Michelia P. ramorum symptoms were limited to necrotic leaf lesions. References: (back to top) Nerium oleander - oleander (Apocynaceae) – is an evergreen shrub or small tree native to the Mediterranean. Growing 3-20 ft. tall and 4-12 ft. wide, its narrow, 4-12 in. long bright green, leathery leaves have a
prominent white midrib. Blooming from late spring to fall, the fragrant, 2-3 in. wide flower clusters grow at twig and branch ends and can be found in shades of white, yellow, pink, salmon, and red. Oleander is an exceptionally tough plant and is commonly planted along California highways. Traditionally Oleander has been used as a heart stimulant and as a skin
treatment for rashes and scabies; however, due to the difficulty of standardizing herbal preparations, and the plant being very poisonous, the use of oleander in self-medication is no longer considered safe. P. ramorum-positive Nerium oleander was found at a Humboldt County nursery, and has since been officially added to the official USDA APHIS
Plants Associated with P. ramorum list. Symptoms included leaf tip necrosis, with the most symptomatic leaf lesions covering up to a quarter of the leaf area. Lesions on oleander, as with most lesions due to Phytophthora infections, were wet and flexible, not dry and crisp. Resources: - Van Wyk, Ben-Erik and Wink, Michael. Medicinal Plants of the World. Portland, OR: Timber Press, Inc., 2004. 215.
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 482.
(back to top) Osmorhiza chilensis (Sweet Cicely) This plant grows in montane, subalpine, and woodland environments, and is a native US perennial herb, occurring mostly in the west and in the northern states, stretching from the east to west. Sweet Cicely is found in open mixed or coniferous forests, forest edges, and thickets. Its erect stem ranges from nine to 40 inches long, and it is branched on the top portion of the plant. The coarsely toothed leaves extend out from a
point into three parts, and further divide into three leaflets. Sweet Cicely flowers and seeds are spread in an upward pointing spray. Its seeds are nearly cylindrical. Its scented flowers are small, greenish-white, organized in loose umbrels, and pollinated by insects. The stems, leaves, seeds, and especially roots of this herb are sweet and often licorice flavored. Hence, the Greek genus name for Sweet Cicely: "osmo" meaning smell and "rhiza" meaning root. The name Chilensis is for
the country of Chile where the plant was first collected in the late 1820s. This herb can be used in teas, stews, or soups. P. ramorum was isolated from Sweet Cicely plants collected at Bouverie Preserve in Sonoma County. The plants were found near heavily infected CA bay laurel and dead and dying coast live oak. Symptoms observed
included leaves with marginal necrosis, necrotic leaf lesions, and leaf dieback. In addition, P. ramorum infected Sweet Cicely was found in Humboldt County in association with P. ramorum infected maidenhair fern, as well as symptomatic CA bay laurel and canyon live oak. The sample was taken from private property west of Redway, near Redwood Creek. Symptoms observed consisted of marginal leaf necrosis, necrotic
leaf lesions, and leaf dieback. Leaf tissue isolations were made, and P. ramorum was recovered. PCR has not been performed. State and federal regulatory officials are reviewing the findings. References: (back to top) Parrotia persica (Persian Parrotia) Parrotia persica – Persian Parrotia – is a deciduous tree or shrub native to Iran. Growing 15' – 35' tall and wide, this slow growing plant is naturally multi-stemmed with low branches and an oval crown. This colorful tree is attractive all year, with autumn foliage turning golden-yellow, then orange to rosy pink, and finally scarlet. The smooth showy
gray bark peels, creating white showy patches and dense clusters of red flowers bloom in late winter or early spring before leafing out occurs. New foliage is seen as reddish purple and matures to a dark green color ranging from 2" – 5" long by 1" – 2" wide. Persian Parrotia prefers full sun or light shade and well-drained soil. It is drought tolerant and needs little pruning, but is susceptible to Japanese beetles. Persian Parrotia was found infected with P. ramorum on one grown plant in South Wales. Symptoms were limited to leaf blight. Culturing, TaqMan PCR, and Koch's postulates have been completed. The identified plant has been destroyed. Resources: - University of Connecticut, Plant Database, "Parrotia persica"
- Brenzel, Kathleen. Sunset Western Garden Book. Menlo Park, CA: Sunset Publishing Corporation, 2001. 497-497.
(back to top) Photinia fraseri (Red tip photinia) Photinia fraseri - Red tip or Fraser's photinia (Rosaceae) is a hardy evergreen shrub native to China that grows 10 – 12 ft. Used as a hedge or informal screen, Fraser's photinia is used for year-round color. Its dense, attractive toothed foliage is 5 inches long and tinged red when young, followed by a glossy dark green color. In the spring, lacy white
flower clusters can be seen, while in the fall it has small red berries. It prefers sun to partial shade and moderate watering. P. ramorum was isolated from Photinia fraseri in 2003 from a nursery in Poland. To date, no symptomatic Red tip has been identified in 2004. Confirmed plants were originally imported from Western Europe.
Symptoms were limited to leaf blight and resembled P. ramorum leaf spots on rhododendron. All symptomatic plants were destroyed; the grower chose to stop growing Red tip at the nursery since it is not an important ornamental plant in Poland. Resources: (back to top) Pyracantha koidzumii (Formosa firethorn) Pyracantha is a genus of shrubs belonging to the rose family (Rosaceae). There are seven species originating from southeast Europe and eastern Asia, in addition to a number of cultivars. Tough, thorny branches and showy orange to red berries characterize this genus. Several cultivars are used for ground cover applications due to their low growth habit. Scarlet firethorn (Pyracantha coccinea), Formosa
firethorn (Pyracantha koidzumii), and Roger's firethorn (Pyracantha rogersiana) are the most popular species for cultivating. Formosa firethorn is native to Taiwan. While grown for its showy,
bright red berries, it is also used as a natural fence, due to its formidable array of thorns and ability to grow up to 12 feet in height. Clusters of white, five-petaled flowers bloom in late spring, followed by a heavy crop of berries ripening in the fall. The berries can persist all winter if not eaten by birds. Firethorns prefer sunny locations (although they will tolerate partial shade), and are good for growing in hot, dry conditions. References:(back to top) Quercus acuta Japanese evergreen oak (Fagaceae) – is an evergreen tree native to East Asia. Growing 20 – 30 ft. in height and 15 – 20 ft. wide, it is round to oval in shape and has dense, low branching,
with smooth grey bark. Leaves of the Japanese evergreen oak grow 2.5 – 5 in. long and are dark green and glossy, with a paler underside, with new growth purplish-brown in color. The monoecious flowers are pollinated by wind, and followed by brown, cupped acorns. After leaching out tannins, tree seeds can be ground into a powder and
used for making bread or as a thickening agent for stews. The roasted seed is also used as a coffee substitute. Medicinally, the galls produced on the tree are strongly astringent and can be used in the treatment of hemorrhages, diarrhea, or dysentery. Additionally, a mulch made of Japanese evergreen oak tree leaves repels slugs and grubs, although fresh leaves should not be used as they may inhibit plant growth. P. ramorum-positive Quercus acuta was found in the United Kingdom (UK). Symptoms included bleeding trunk cankers. Consequently, USDA APHIS has added this species to the list of regulated Plants Associated with Phytophthora ramorum. Resources: (back to top) Quercus cerris (European Turkey oak)European Turkey oak is native to Mediterranean Europe and Asia. While
not commonly grown in the US, it is climatically suitable in a band from the mid-Atlantic states through the southern plain states and north through the Rocky Mountain states. (There is another shrubby oak native to the US with the common name turkey oak - Quercus laevis.). European Turkey oak, a deciduous oak, is widely planted and naturalized
in much of Europe. With a fast growth rate, it may grow to be 130 feet, but is generally 30 - 50 ft tall (see photo), and is used in windbreaks, and as an ornamental (see photo). P. ramorum caused bleeding cankers on the infected European Turkey
oak found near Cornwall. European Turkey oak is in the section Cerris, a division of the genus Quercus, that only includes Eurasian species; it is neither a white nor a red oak (see Quercus species list). Quercus ilix (Holm oak)Holm oak, also called holly oak or evergreen oak, is a large evergreen oak tree native to the Mediterranean region, where it tends to grow on dry limestone hillsides. Similar to holly leaves, holm oak leaves are glossy, leathery, variably shaped, and, where lobes are present, the tips contain a single spine. Holm oak grows in much of maritime northern Europe, but is intolerant of cold continental winters. In the US, it is adaptable to climate zones in the southeast states and the Pacific Coast (see photo). With a rounded crown and pendulous low-hanging branches, its size and solid evergreen character make it desirable for urban and garden settings (see photo). P. ramorum affected only the leaves of the four infected holm oaks detected in Cornwall. In California, P. ramorum infects oak through the
bark, primarily only oaks in the red oak group are susceptible, and the leaves are not infected. Holm oak is a member of the white oak group, which may explain why the leaves are susceptible. References (European Turkey oak and Holm oak): |
