Sirococcus clavigignenti-juglandacearum (butternut canker)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- List of Symptoms/Signs
- Biology and Ecology
- Means of Movement and Dispersal
- Detection and Inspection
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Sirococcus clavigignenti-juglandacearum Nair, Kostichka and Kuntz
Preferred Common Name
- butternut canker
International Common Names
- French: chancre du noyer cendre
Local Common Names
- Germany: Sirococcus-Krebs der Walnuss
- SIROCJ (Sirococcus clavigignenti-juglandacearum)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Ascomycota
- Subphylum: Pezizomycotina
- Class: Sordariomycetes
- Subclass: Sordariomycetidae
- Order: Diaporthales
- Genus: Sirococcus
- Species: Sirococcus clavigignenti-juglandacearum
Notes on Taxonomy and NomenclatureTop of page
DescriptionTop of page
DistributionTop of page
Since the genus Juglans and the Juglandaceae are, besides North America and Europe, distributed in Asia and in South America, it must be presumed that S. clavigignenti-juglandacearum originates in one or other of the latter.
S. clavigignenti-juglandacearum is absent in the European and Mediterranean region. In North America it is present in Canada (at least in Ontario, Québec and New Brunswick), and in the USA (spread across the entire range of butternut).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 12 May 2022
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Netherlands||Absent, Confirmed absent by survey|
Risk of IntroductionTop of page
It seems very likely that the fungus would, in southern Europe, encounter similar conditions to those in which it has been so damaging in North America. European Juglans spp. carry insects of the same families as those thought to act as vectors in North America (Schwenke, 1974). As in North America, reliable control measures are not available. Current American research on resistance in J. cinerea would not protect the Juglandaceae which grow in Europe.
According to Patterson (1993), S. clavigignenti-juglandacearum is much more aggressive than the fungi which caused chestnut blight (Cryphonectria parasitica; EPPO/CABI, 1997) and Dutch elm disease (Ophiostoma ulmi/Ophiostoma novo-ulmi). Furthermore, though the main pathways which were involved in the spread of these fungi (plants for planting, wood) are probably not of great importance in practice for S. clavigignenti-juglandacearum, the latter can be carried in infected nuts which carry a significant risk of casual introduction. There is general agreement among experts on the disease (e.g. Orchard, 1984; Fleguel, 1996; Nair, 1999) that the fungus presents a high risk to other continents and justifies phytosanitary measures. The seed transferability of the pathogen is one of the main risk factors to be considered when measures against the introduction of the fungus are taken. Thus, S. clavigignenti-juglandacearum presents a high risk to the European and Mediterranean region (Schröder et al., 2002) in that it is likely to kill large numbers of valuable trees used for economic production of wood, nuts and oil. It also threatens walnut as an amenity species widely planted throughout the European and Mediterranean region.
Hosts/Species AffectedTop of page
The main host is Juglans cinerea (butternut, white walnut, oilnut), which is native to North America. It is the only species that is killed by the pathogen, though other Juglans species and hybrids are diseased to varying degrees. Two other hosts are naturally infected in North America: Juglans nigra (black walnut) and Juglans ailanthifolia var. cordiformis (heartnut), but infrequently and only when standing among heavily infected butternut trees (Kuntz et al., 1979; Ostry, 1997a; Ostry et al., 1997). Some other Juglandaceae were found to be susceptible on artificial inoculation in laboratory experiments: Juglans regia, J. ailanthifolia, and various hybrids (Orchard et al., 1982). Laboratory experiments by Ostry (1997b) indicated that S. clavigignenti-juglandacearum might be able to survive on other Juglandaceous hosts (Carya spp.) and possibly other trees (Quercus, Prunus).
The most important potential host in the European and Mediterranean region is Juglans regia (walnut), an Asian species which is widely planted throughout most of Europe except the north. It needs mild winters without late frosts, and a climate which is not too dry. It can grow up to an elevation of 800 m, in the Alps up to 1200 m. Hungary, Turkey, Italy and France have commercial plantations of J. regia (Bernyi et al., 1991; Schütt et al., 1992), to produce nuts, oil or the valuable wood. In these countries and in many others, individual trees of J. regia are common in farms and gardens, providing nuts locally. Juglans nigra from North America, and J. × intermedia (J. regia × J. nigra), are also planted on a smaller scale, and used as rootstocks for J. regia.
Juglans spp. are also grown as amenity trees in parks and sold in nurseries (e.g. J. nigra, J. ailanthifolia). The main host of S. clavigignenti-juglandacearum (J. cinerea) is, however, only grown to a very limited extent in Europe.
Host Plants and Other Plants AffectedTop of page
|Carya cordiformis (bitternut hickory)||Juglandaceae||Unknown|
|Carya illinoinensis (pecan)||Juglandaceae||Unknown|
|Carya ovata (shagbark hickory)||Juglandaceae||Unknown|
|Castanea dentata (American chestnut)||Fagaceae||Unknown|
|Castanea mollissima (hairy chestnut)||Fagaceae||Unknown|
|Corylus americana (American hazel)||Betulaceae||Unknown|
|Corylus cornuta (beaked hazel)||Betulaceae||Unknown|
|Juglans ailantifolia var. cordiformis||Juglandaceae||Other|
|Juglans cinerea (butternut)||Juglandaceae||Main|
|Juglans nigra (black walnut)||Juglandaceae||Other|
|Juglans regia (walnut)||Juglandaceae||Main|
|Prunus serotina (black cherry)||Rosaceae||Unknown|
|Quercus alba (white oak)||Fagaceae||Unknown|
|Quercus macrocarpa (mossy-cup oak)||Fagaceae||Unknown|
|Quercus rubra (northern red oak)||Fagaceae||Unknown|
|Quercus velutina (black oak)||Fagaceae||Unknown|
SymptomsTop of page
Another fungus, Melanconis juglandis (anamorph: Melanconium oblongum Berk.), often causes secondary infection (Nicholls et al., 1978), and has been confused with S. clavigignenti-juglandacearum. M. juglandis does not cause cankers. Its anamorphic fruiting bodies appear as very small, dark, smooth bumps on the bark, releasing inky black masses of spores. Spores are usually asymmetrically ovoid, dark and non-septate (Nicholls et al., 1978).
List of Symptoms/SignsTop of page
|Stems / canker on woody stem|
Biology and EcologyTop of page
S. clavigignenti-juglandacearum was first described by Nair et al. (1979), and its pathogenicity has been demonstrated according to Koch's postulates. Up to now, the teleomorph of the fungus has not been discovered (Furnier et al., 1999). Conidia develop beneath infected bark in sticky masses. Stromatal pegs lift and rupture the bark and, under moist conditions, millions of conidia are extruded in colourless cirri from globose to flattened, single or confluent pycnidia borne in the stroma among the hyphal pegs. These conidia are dispersed by rain splash and wind in little droplets or as aerosols during rainfall (Kuntz et al., 1979; Tisserat and Kuntz, 1983b). Relative humidity of 95-100% was found to aid successful infection greatly (Federspiel and Nair, 1982). Conidia are transported by run-off water from infected branches to tree trunks, infecting wounds and other openings. This results in multiple stem cankers.
The tree is first infected through buds and openings like lenticels, cracked bark, or leaf scars (Kuntz et al., 1979; Ostry, 1997b). Cankers on twigs start to develop, usually in the lower crown, due to the favourable microclimatic conditions in this part of the tree (the branches in the lower crown tend to retain the moisture necessary for spore germination for longer periods than in the upper crown; Tisserat and Kuntz, 1984). Spores of S. clavigignenti-juglandacearum require at least 16 h of dew at 20°C to germinate on the bark of J. cinerea.
In infected suckers, twigs and branches, cell walls of the bark are degraded, macerated and rapidly broken up entirely, resulting in a dark brown sticky residue and a brown exudate. The fungal hyphae penetrate the phloem parenchyma intracellularly and between the phloem fibre elements intercellularly. They advance intracellularly through the uni- and multiseriate xylem ray cells and parenchyma cells. In infected J. cinerea and J. nigra, hyphae in the xylem ray cells appeared larger and darker than those in xylem parenchyma cells. From the xylem, hyphae progress finally into other bark and wood tissues (Kuntz et al., 1979; Nair, 1999). Hyphae also grow beyond cankered tissue, creating new cankers when reaching the cambium (Sinclair et al., 1987).
The fungus is able to sporulate on standing or felled dead trees for at least 20 months (Tisserat and Kuntz, 1982, 1984). Outside the host, conidia can survive for at least 8 h in cool and cloudy weather (Tisserat and Kuntz, 1983c). The pathogen remains viable in diseased tissue and in culture down to 0°C and below. The fungus is seedborne, at least in seeds of J. cinerea and J. nigra (Orchard, 1984; Innes, 1997). This partially explains why J. cinerea does not regenerate after early infection and killing of trees (Ostry, 1997b). In a glasshouse experiment, seedlings of J. cinerea were killed soon after emergence from seeds derived from infected trees that were stratified with intact husks (Orchard, 1984). Additionally, the seedlings are highly susceptible to the fungus and die quickly after infection. It is accordingly not likely that young plants would carry the pathogen if traded as plants for planting. There is no evidence that the fungus can spread on seed or seedlings of J. ailanthifolia.
Means of Movement and DispersalTop of page
Spores are dispersed by rain or mist over short distances. By wind, spores can be transported up to 45 m (Tisserat et al., 1981; Tisserat, 1982). Small droplets or aerosols with conidia may be swept above the tree canopy by turbulent air and may possibly spread by wind over distances of more than 1 km (Tisserat and Kuntz, 1983c). Insects, including sap and tissue feeders, are thought to be responsible for long-distance spread of the fungus. Birds may also be vectors. Additionally, insects or birds may, by causing wounds, increase points for infection (Ostry et al., 1994; Nair, 1999). Ostry (1997b) found the fungus on the beetles Laemophlaeus fasciatus, Laemophloeus testareus (Laemophloeidae) and Bactridium spp. (Monotomidae). Halik and Bergdahl (1996; 2002), Bergdahl and Halik (1997) and Katovich and Ostry (1998) found it on Acoptus suturalis (Curculionidae), Astylopsis macula (Cerambycidae), Cossonus platalea (Curculionidae), Eubulus parochus (Curculionidae), Hyperplatys maculata (Cerambycidae), Laemophlaeus biguttatus (Laemophloeidae), and Glischrochilus quadrisignatus (Nitidulidae). Up to 44% of the collected specimens of A. macula and 38% of the specimens of E. parochus carried conidia of S. clavigignenti-juglandacearum. However, disease transmission by these insects does not seem to have been demonstrated.
According to Orchard (1984) and Innes (1997), the fungus can be internally seedborne on J. cinerea and J. nigra, surviving in the cotyledons of infected seed stratified at 4°C up to 18 months (Prey et al., 1997). Seedlings from infected seeds develop basal lesions, stem cankers, stroma, pycnidia and hyphal pegs and die rapidly (Orchard, 1984). Thus, internally infected seeds from infected trees could be present an important pathway for moving S. clavigignenti-juglandacearum to new areas. Movement of scion wood and other propagative material, as well as untreated logs and firewood with bark from diseased trees, may add to the dispersal of the fungus.
ImpactTop of page
S. clavigignenti-juglandacearum presents a threat to biodiversity in North America. Due to the extensive mortality caused by the fungus and the large amount of already infected trees, J. cinerea was listed as a threatened and endangered species in the USA (Category 2 - more information required prior to formal listing; Ostry et al., 1994), but this category has been eliminated and currently J. cinerea has no official listing status. In Canada, butternut was listed as an endangered species by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in November 2003.
Detection and InspectionTop of page
Artificial inoculation of J. cinerea, as described by Federspiel and Nair (1982) and Gabka (1996), leads to blackening of the inner bark tissue in 6 days (8 for J. nigra). Removal of the bark reveals a brown to black elliptical area of killed cambium (Ostry, 1997b).
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.Up to now, there is no effectively applied control against S. clavigignenti-juglandacearum. The fungicides benomyl and chlorothalonil have been found to be effective preventive products in laboratory experiments (Nicholls, 1979), but were not approved in the field. Even if an effective mechanical method, fungicide or biocontrol agent existed, it would be difficult to apply it due to the scattered distribution of susceptible trees. Removal of recently killed and visibly infected trees may reduce the amount of inoculum only locally (Nair, 1999).
The only possibility for successful control of the fungus seems to be the selection of resistant forms. Resistance varies greatly between individual trees and is possibly heritable (Ostry, 1997b). Studies are in progress to find, graft, propagate and plant resistant trees of J. cinerea in the USA (Ostry, 1997b).
S. clavigignenti-juglandacearum was added in 2005 to the EPPO A2 action list, and EPPO member countries are thus recommended to regulate it as a quarantine pest. Suggested measures could include the prohibition of import of host plants for planting (including seeds) from countries where the pest occurs, or as appropriate origin from a pest-free area or pest-free place of production. It may be noted that J. regia is produced in USA nearly entirely in California, where natural infestation of J. regia has not yet been observed and the fungus does not occur (movement of Juglans spp. from eastern USA to California is restricted).
As a preventive measure in the European and Mediterranean region, countries could restrict the planting of J. cinerea and avoid planting other Juglans spp. in the vicinity of J. cinerea. If the fungus is locally introduced into Europe, measures may also be needed for movement of walnut wood.
ReferencesTop of page
Anderson RL, LaMadeleine LA, 1977. The Occurrence of Butternut Decline in the United States. Northeast Area State and Private Forestry Survey Report S-2 -77. Washington, USA: USDA Forest Service
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Bernyi G, Csurka E, Srvri J and Szodfridt I, 1991. [Experience with walnut forests in Hungary.] Allgemeine Forst Zeitschrift für Waldwirtschaft und Umweltvorsorge, 12: 619-621 (in German)
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Broders, K. D., Boland, G. J., 2010. Molecular diagnostic assay for detection of the butternut canker pathogen Sirococcus clavigignenti-juglandacearum. Plant Disease, 94(8), 952-958. doi: 10.1094/PDIS-94-8-0952
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