Calonectria pseudonaviculata (Buxus blight)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Plant Trade
- Impact Summary
- Economic Impact
- Risk and Impact Factors
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Gaps in Knowledge/Research Needs
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard, M.J. Wingf. & Crous, 2010
Preferred Common Name
- Buxus blight
Other Scientific Names
- Cylindrocladium buxicola Henricot 2002
- Cylindrocladium pseudonaviculatum Crous, J.Z. Groenew. & C.F. Hill, 2002
International Common Names
- English: box blight; boxwood blight; boxwood leaf drop; leaf and twig blight of box
- CYLDBU (Cylindrocladium buxicola)
Summary of InvasivenessTop of page
C. pseudonaviculata is an asexual species in a genus of common ascomycete plant pathogens. It was identified relatively recently in the UK, as an introduced species causing a devastating shoot blight of boxwood [Buxus spp.] plants that are commonly used in gardens and landscaping. The full extent of its host range is not known, but Buxus spp. from different continents were found to be susceptible (Henricot et al., 2008). It was placed on the EPPO Alert list in 2004, as it appeared to be spreading to the mainland (EPPO, 2009a), and removed from the list in 2008. This pathogen has been reported from additional European countries in recent years, and may have been transported in asymptomatic infected plants or propagating materials. It survives well in plant debris and probably also in soil.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Ascomycota
- Subphylum: Pezizomycotina
- Class: Sordariomycetes
- Subclass: Hypocreomycetidae
- Order: Hypocreales
- Family: Nectriaceae
- Genus: Calonectria
- Species: Calonectria pseudonaviculata
Notes on Taxonomy and NomenclatureTop of page
Cylindrocladium pseudonaviculatum was first described by Crous et al. (2002). The description of Cylindrocladium buxicola followed a few months later in the same year (Henricot and Culham, 2002), which later proved to be synonymous with Calonectria pseudonaviculata (Lombard et al., 2010). The taxon was determined to be a new species both by examination of morphology and comparison of sequences of several regions of nuclear DNA. No sexual morph could be obtained by mating of single spore cultures on carnation leaf agar (CLA), and the similarity of amplified fragment length polymorphism (AFLP) profiles of the different isolates indicated that all were probably descended from one clone.
Sexual morphs of Cylindrocladium species are members of Calonectria, in the Hypocreales (Rossman, 1993; Crous, 2002). The current scientific name for this species is Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard, M.J. Wingf. & Crous.
DescriptionTop of page
Conidiophores comprised of a stipe, sterile stipe extension with a terminal vesicle, and penicillate arranged branches bearing phialides. Stipe septate, hyaline, 95-155 µm, the stipe extension terminating in a broadly ellipsoid vesicle, vesicle apex pointed to papillate, 6.5-11.0 µm diameter, the widest part above the middle. Primary branches 0-1-septate, (5-)15-41(-66) x 3-5 µm, secondary branches aseptate, (11-)13-25(-35) x 3-5 µm, tertiary branches rare. Terminal branches bearing two to five phialides. Phialides reniform, hyaline, aseptate, (10-)13-18(-21) x 2.5-5.0 µm. Conidia cylindrical, straight, hyaline, 1-septate, the ends rounded, 42-68 x 4-6 µm, in slimy clusters. Chlamydospores on carnation [Dianthus caryophyllus] leaves dark-brown, thick-walled, forming microsclerotia. Reverse of colony on malt extract agar (MEA) fuscous black at centre fading through sienna outwards. Mycelium at margin white. For additional details, see Henricot and Culham (2002).
DistributionTop of page
The new disease of boxwood (Buxus spp.) was first observed in 1994 in the UK, and a more severe outbreak occurred in 1997 (Henricot and Culham, 2002). Although the pathogen is considered to have been recently introduced (Brasier, 2008), it was already widespread in the UK by 2000 (Henricot et al., 2000). An isolate from New Zealand was determined by Henricot and Culham (2002) to be of the same species and closely related to the strains in the UK. Reports of C. pseudonaviculata have since come from Belgium, Ireland, Germany and the Netherlands (CABI/EPPO, 2012; Henricot et al., 2008), Italy (Saracchi et al., 2008; EPPO, 2013), Austria (EPPO, 2013) and Spain (Pintos Varela et al., 2009) suggesting that it spread from the UK to mainland Europe.
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.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Georgia (Republic of)||Present||Gorgiladze et al., 2011; CABI/EPPO, 2012; Gasich et al., 2013; EPPO, 2014|
|Iran||Present||Mirabolfathy et al., 2013; EPPO, 2014|
|Turkey||Present||Akilli et al., 2012; EPPO, 2014|
|Canada||Restricted distribution||CABI/EPPO, 2012; EPPO, 2014|
|-British Columbia||Restricted distribution||CABI/EPPO, 2012; Elmhirst et al., 2013; EPPO, 2014|
|-Ontario||Present, few occurrences||CABI/EPPO, 2012|
|-Quebec||Present, few occurrences||CABI/EPPO, 2012|
|USA||Restricted distribution||CABI/EPPO, 2012; EPPO, 2014|
|-Connecticut||Present||NAPPO, 2011; CABI/EPPO, 2012; Ivors et al., 2012; EPPO, 2014|
|-Delaware||Present||Malapi-Wight et al., 2014|
|-Florida||Present||Iriarte et al., 2016|
|-Kentucky||Present||Gauthier et al., 2016|
|-Maryland||Present||CABI/EPPO, 2012; EPPO, 2014; Malapi-Wight et al., 2014|
|-Massachusetts||Present||CABI/EPPO, 2012; EPPO, 2014|
|-New Jersey||Present||Malapi-Wight et al., 2014|
|-New York||Present||CABI/EPPO, 2012; EPPO, 2014; Malapi-Wight et al., 2014|
|-North Carolina||Present||NAPPO, 2011; CABI/EPPO, 2012; Ivors et al., 2012; EPPO, 2014|
|-Oregon||Present||CABI/EPPO, 2012; EPPO, 2014|
|-Pennsylvania||Present||CABI/EPPO, 2012; EPPO, 2014|
|-Rhode Island||Present||CABI/EPPO, 2012; EPPO, 2014|
|-Virginia||Present||NAPPO, 2011; CABI/EPPO, 2012; EPPO, 2014; Kong et al., 2017|
|Austria||Present, few occurrences||Introduced||CABI/EPPO, 2012; EPPO, 2014|
|Belgium||Widespread||Introduced||Invasive||Crepel and Inghelbrecht, 2003; CABI/EPPO, 2012; EPPO, 2014|
|Croatia||Restricted distribution||Cech et al., 2010; CABI/EPPO, 2012; EPPO, 2014|
|Czech Republic||Restricted distribution||CABI/EPPO, 2012; Safránková et al., 2012; EPPO, 2014|
|France||Present||Introduced||Invasive||Crepel and Inghelbrecht, 2003; CABI/EPPO, 2012; Saurat et al., 2012; EPPO, 2014|
|Germany||Widespread||Introduced||Invasive||Brand, 2005; Henricot et al., 2008; CABI/EPPO, 2012; EPPO, 2014||First seen 2004|
|Ireland||Present||Introduced||Invasive||Henricot et al., 2008; CABI/EPPO, 2012; EPPO, 2014|
|Italy||Restricted distribution||Introduced||2007||Invasive||Saracchi et al., 2008; CABI/EPPO, 2012; EPPO, 2014|
|-Italy (mainland)||Present, few occurrences||CABI/EPPO, 2012|
|Netherlands||Present||Introduced||Invasive||Henricot et al., 2008; CABI/EPPO, 2012; EPPO, 2014|
|Norway||Restricted distribution||EPPO, 2014|
|Slovenia||Present||CABI/EPPO, 2012; EPPO, 2014|
|Spain||Present||Introduced||Invasive||Pintos et al., 2009; CABI/EPPO, 2012; EPPO, 2014|
|-Spain (mainland)||Present, few occurrences||CABI/EPPO, 2012|
|Sweden||Present, few occurrences||CABI/EPPO, 2012; EPPO, 2014|
|Switzerland||Present||Introduced||Invasive||Saracchi et al., 2008; CABI/EPPO, 2012; EPPO, 2014|
|UK||Widespread||Introduced||Invasive||Henricot et al., 2000; Henricot and Culham, 2002; CABI/EPPO, 2012; EPPO, 2014|
|-England and Wales||Widespread||CABI/EPPO, 2012; EPPO, 2014|
|-Scotland||Present||CABI/EPPO, 2012; EPPO, 2014|
|New Zealand||Present||Introduced||Invasive||Crous et al., 2002; Henricot and Culham, 2002; CABI/EPPO, 2012; EPPO, 2014|
IntroductionsTop of page
Risk of IntroductionTop of page
The origin of C. pseudonaviculata is not known; it is considered to be an introduced alien species in the UK, where it was first identified (Brasier, 2008). Transmission of the pathogen on asymptomatic Buxus plants, as suggested by Henricot and Culham (2002), may be responsible for its rapid spread in the UK and to various countries of Western Europe. It is also possible, given the wide host ranges of some Calonectria spp. and the possibility of their misidentification (see Henricot and Culham, 2002; Lombard et al. 2010), that an introduction on some other host went unchallenged because the fungus resembled a widespread species.
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
The disease has only been found in some cultivars of three species out of the 91 in the genus Buxus worldwide: B. sempervirens,B. microphylla and B. sinica var. insularis (Henricot et al., 2008). When detached stems of other species, including plants native to four continents, were tested beside these, Henricot et al. (2008) found no immunity to the fungus. Differences between the species were not consistent in tests with different isolates of the pathogen. The lowest level of disease was observed in B. balearica, B. riparis and a Sarcococca sp.Sarcococca is a genus in the Buxaceae that includes some species imported for use as ground cover; Pachysandra species, also members of the family often used for ground cover, were not tested (Henricot et al., 2008).
Host Plants and Other Plants AffectedTop of page
|Buxus microphylla (little-leaf box)||Buxaceae||Main|
|Buxus microphylla var. japonica||Buxaceae||Main|
|Buxus sempervirens (common boxwood)||Buxaceae||Main|
|Buxus sinica (chinese box)||Buxaceae||Main|
|Buxus sinica var. insularis (Korean boxwood)||Buxaceae||Main|
|Pachysandra terminalis (Japanese spurge)||Buxaceae||Other|
|Sarcococca hookeriana var. digyna||Buxaceae||Other|
Growth StagesTop of page Vegetative growing stage
SymptomsTop of page
The fungus causes dark-brown leaf spots, which may coalesce to cover whole leaves, black streaks on stems that appear to progress from the bottom of the plant to the top, and severe defoliation and dieback (Henricot et al., 2000, 2008; Henricot and Culham, 2002).
List of Symptoms/SignsTop of page
|Growing point / dieback|
|Leaves / abnormal leaf fall|
|Leaves / necrotic areas|
|Stems / dieback|
|Stems / discoloration of bark|
Biology and EcologyTop of page
Conidia dispersed in water germinated on Buxus leaves beginning 3 hours after inoculation. Germ tubes penetrated through stomata or directly through the cuticle without forming an appressorium. Conidiophores were produced on the leaf surface after 7 days in a moist chamber at 20°C (Henricot et al., 2008). High humidity is required for infection of inoculated plants (Henricot et al., 2000).
In culture on PCA (potato-carrot agar), optimum growth occurs at 25°C. Growth is very slow at 27.5°C, and no growth was observed at 30°C. Incubation at 33°C for 7 days is lethal, and the low limit for growth is above 5°C (Henricot and Culham, 2002).
Mycelium of the fungus survived 5 years in decomposing leaves on or in soil in southern England, but microsclerotia were not seen (Henricot et al., 2008). Most Calonectria species are readily recovered from soil (Crous, 2002).
No sexual reproductive structures have been observed in nature or in culture. The UK isolates examined by Henricot and Culham (2002), as well as one from New Zealand, exhibited little variation in AFLP patterns, thus appearing to be derived from one clone.
ClimateTop of page
|Cf - Warm temperate climate, wet all year||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year|
Means of Movement and DispersalTop of page
The 'slimy' conidia are easily splash-dispersed by water (Crous, 2002).
None is reported, but Crous (2002) hypothesizes a role for the stipe extension vesicle in attracting insects to the conidiophore.
The fungus could be brought into gardens or nurseries on asymptomatic plants (Henricot et al., 2008).The means of introduction into the UK and mainland Europe could be the same, but is not known. In a nursery in Italy, potted plants that became infected had been without symptoms when imported from Belgium, where the pathogen was known to be present (Saracchi et al., 2008).
Pathway CausesTop of page
Pathway VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||hyphae||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Leaves||hyphae; spores||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Stems (above ground)/Shoots/Trunks/Branches||hyphae; spores||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|True seeds (inc. grain)|
Impact SummaryTop of page
Economic ImpactTop of page
The disease is described as 'devastating' to boxwood (Buxus spp.) plants, which are widely used as landscape ornamentals (Henricot et al., 2008). Infected imported potted plants in an Italian nursery were destroyed due to the severity of disease (Saracchi et al., 2008).
Risk and Impact FactorsTop of page Invasiveness
- Highly mobile locally
- Long lived
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Host damage
- Negatively impacts agriculture
- Negatively impacts livelihoods
- Reduced amenity values
- Highly likely to be transported internationally accidentally
- Difficult to identify/detect as a commodity contaminant
DiagnosisTop of page
Isolates may be grown on PCA (potato-carrot agar), but culture on carnation leaf agar at 25°C under near-UV light is required for production of conidiophores with diagnostic morphology (Crous and Wingfield, 1994).
Comparison of sequences of the ITS region is insufficient to distinguish all the known species of Calonectria (Crous et al., 1999; Henricot and Culham, 2002). Instead, sequences of the 5' end of the beta-tubulin gene, the HMG box of the MAT2 gene, and partial sequences of the histone H3 gene have been used (Crous et al., 1999, 2002, 2006; Henricot and Culham, 2002). Most of these sequences, including at least eight for C. pseudonaviculata, are available in the GenBank database for comparison (Lombard et al., 2010).
Detection and InspectionTop of page
This pathogen causes dark leaf spots, dark streaks on the stems, and eventual defoliation of Buxus species. Conidiophores bearing clusters of distinctive large cylindrical conidia and a vesicle-tipped sterile stipe extension are produced on shoots incubated in a moist chamber at 20°C (Henricot and Culham, 2002).
Similarities to Other Species/ConditionsTop of page
Calonectria pseudonaviculata is distinguished from C. morganii and C. pyrochroa by the shape of the terminal vesicle and the size and septation of its conidia (Henricot and Culham, 2002). The vesicles of C. morganii are not pointed, and those of C. pyrochroa are spathulate to clavate. In addition, C. morganii and C. pyrochroa grow at 30°C and above (Crous and Wingfield, 1994) whereas 30°C is the maximum growth temperature for C. pseudonaviculata (Henricot and Culham, 2002). Other species, C. pauciramosa and C. mexicana, that have somewhat similar vesicles, are also warm-temperature species, with growth maxima of 30°C or above (Henricot and Culham, 2002).
Prevention and ControlTop of page
The likelihood that the pathogen is transported across borders in asymptomatic plants (Henricot et al., 2008; Saracchi et al., 2008) would require restriction of trade of boxwood (Buxus spp.) plants and vegetative propagating material, such as cuttings, including either quarantine or certification procedures to prevent further spread of the fungus. If there is a possibility that it was, or can be, introduced on other hosts upon which it has been misidentified, stricter attention to identifications of Calonectria pathogens, with the aid of molecular methods, may be necessary.
Cultural Control and Sanitary Measures
C. pseudonviculata can persist for years in plant debris on or in the ground, therefore removing infected twigs, fallen leaves and the topsoil under affected plants are reasonable efforts to reduce inoculum (Henricot et al., 2008). Batdorf (2004) asserts that regular fall pruning to thin the branches of Buxus sempervirens "Suffruticosa" will control fungal foliage diseases such as Cylindrocladium blight.
Henricot et al. (2008) tested a number of fungicide products available in the UK. Those most effective at inhibiting mycelial growth of C. pseudonaviculata in vitro were carbendazim, prochloraz, kresoxim-methyl, penconazole, the combination of epiconazole and pyraclostrobin, and the combination of epiconazole+kresoxim-methyl+pyraclostrobin. Those most effective at inhibiting conidial germination in vitro were azoxystrobin, chlorothalonil, kresoxim-methyl, mancozeb, boscalid+pyraclostrobin, epiconazole+pyraclostrobin, and the combination of epiconazole+kresoxim-methyl+pyraclostrobin. Carbendazim, myclobutanil, penconazole and prochloraz had little or no effect on germination.
Chlorothalonil, which was the most inhibiting to spore germination in vitro, has also been reported as effective in the field (Henricot et al., 2008).
Differences in isolate-species interactions observed by Henricot et al. (2008) suggest a potential for use of varieties and species in landscaping of areas where the pathogen is known to occur. Unfortunately, the growth habit that contributes to the ornamental desirability of the susceptible species and varieties may favour the development of disease (Henricot et al., 2008).
Gaps in Knowledge/Research NeedsTop of page
Many Calonectria species infect roots (Crous, 2002); whether C. pseudonaviculata can infect those of Buxus or other plants, should be investigated. The possible role of chlamydospores and microsclerotia in survival in plant tissues and in soil should be examined further. Efforts to discover the origin of the fungus and to explore the possibility of insect vectors for Calonectria species could help to prevent further introductions.
ReferencesTop of page
Akilli S; Katircioglu YZ; Zor K; Maden S, 2012. First report of box blight caused by Cylindrocladium pseudonaviculatum in the Eastern Black Sea region of Turkey. New Disease Reports, 25:23. http://www.ndrs.org.uk/article.php?id=025023
Brand T, 2005. Occurrence of Cylindrocladium buxicola B. Henricot on boxwood in Northwest-Germany. (Auftreten von Cylindrocladium buxicola B. Henricot an Buchsbaum in Nordwest-Deutschland.) Nachrichtenblatt des Deutschen Pflanzenschutzdienstes, 57(12):237-240.
Elmhirst JF; Auxier BE; Wegener LA, 2013. First report of box blight caused by Cylindrocladium pseudonaviculatum (C. buxicola) in British Columbia, Canada. Plant Disease, 97(4):559-560. http://apsjournals.apsnet.org/loi/pdis
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Gasich EL; Kazartsev IA; Gannibal PhB; Koval AG; Shipilova NP; Khlopunova LB; Ovsyannikova EI, 2013. Calonectria pseudonaviculata - a new for Abkhazia species, the causal agent of boxwood blight. Mikologiya i Fitopatologiya, 47(2):129-131. http://www.nauka.nw.ru
Gorgiladze L; Meparishvili G; Sikharulidze Z; Natsarishvili K; Davitadze R, 2011. First report of box blight caused by Cylindrocladium buxicola in Georgia. New Disease Reports, 23:Article 24. http://www.ndrs.org.uk/pdfs/023/NDR_023024.pdf
Iriarte F; Paret M; Knox G; Schubert T; Jeyaprakash A; Davison D, 2016. First report of boxwood blight caused by Calonectria pseudonaviculata in Florida. Plant Health Progress, No.October:PHP-BR-16-0027. http://www.plantmanagementnetwork.org/php/elements/sum2.aspx?id=10932
Ivors KL; Lacey LW; Milks DC; Douglas SM; Inman MK; Marra RE; LaMondia JA, 2012. First report of boxwood blight caused by Cylindrocladium pseudonaviculatum in the United States. Plant Disease, 96(7):1070. http://apsjournals.apsnet.org/loi/pdis
Kong P; Likins TM; Hong CX, 2017. First report of blight of Sarcococca hookeriana var. humilis by Calonectria pseudonaviculata in Virginia. Plant Disease, 101(1):247-248. http://apsjournals.apsnet.org/loi/pdis
LaMondia JA; Li DW, 2013. Calonectria pseudonaviculata can cause leaf spot and stem blight of Pachysandra procumbens. Plant Health Progress, No.February:0226-01-PHP-2013-0226-01-BR. http://www.plantmanagementnetwork.org/php/
LaMondia JA; Li DW; Marra RE; Douglas SM, 2012. First report of Cylindrocladium pseudonaviculatum causing leaf spot of Pachysandra terminalis. Plant Disease, 96(7):1069. http://apsjournals.apsnet.org/loi/pdis
Lombard L; Crous PW; Wingfield BD; Wingfield MJ, 2010. Phylogeny and systematics of the genus Calonectria. Studies in Mycology, 66:31-69.
Malapi-Wight M; Hebert JB; Buckley R; Daughtrey ML; Gregory NF; Rane K; Tirpak S; Crouch JA, 2014. First report of boxwood blight caused by Calonectria pseudonaviculata in Delaware, Maryland, New Jersey, and New York. Plant Disease, 98(5):698. http://apsjournals.apsnet.org/loi/pdis
Mirabolfathy M; Ahangaran Y; Lombard L; Crous PW, 2013. Leaf blight of Buxus sempervirens in northern forests of Iran caused by Calonectria pseudonaviculata. Plant Disease, 97(8):1121-1122. http://apsjournals.apsnet.org/loi/pdis
NAPPO, 2011. Phytosanitary Alert System: Detection of boxwood blight, Cylindrocladium pseudonaviculatum, in Connecticut, North Carolina, and Virginia. Phytosanitary Alert System: Detection of boxwood blight, Cylindrocladium pseudonaviculatum, in Connecticut, North Carolina, and Virginia. NAPPO. http://www.pestalert.org/oprDetail.cfm?oprID=508
Pintos Varela C; González Penalta B; Mansilla Vázquez JP; Aguín Casal O, 2009. First report of Cylindrocladium buxicola on Buxus sempervirens in Spain. Plant Disease, 93(6):670. http://apsjournals.apsnet.org/loi/pdis
Rossman AY, 1993. Holomorphic Hypocrealean fungi: Nectria sensu stricto and teleomorphs of Fusarium. In: The Fungal Holomorph: Mitotic, Meiotic and Pleomorphic Speciation in Fungal Systematics [ed. by Reynolds, D. R.\Taylor, J. W.]. Wallingford, UK: CAB International, 149-160.
Saracchi M; Rocchi F; Pizzatti C; Cortesi P, 2008. Box blight, a new disease of Buxus in Italy caused by Cylindrocladium buxicola. Journal of Plant Pathology, 90(3):581-584. http://www.sipav.org/main/jpp/
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29/01/10 Original text by:
Distribution MapsTop of page
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