Calonectria pteridis Crous, M. J. Wingf. & Alfenas, 1993

California Pest Rating for
Calonectria pteridis Crous, M. J. Wingf. & Alfenas, 1993
Pest Rating: B

Initiating Event:

On April 19, 2016, diseased Ravenea rivularis (majesty palm) plants exhibiting leaf spots were intercepted by San Luis Obispo County Agricultural officials. The shipment of plants had originated in Florida and was destined to a nursery in San Luis Obispo County.  Symptomatic leaves were sent to the CDFA Plant Pest Diagnostics Branch for diagnosis.  Suzanne Latham, CDFA plant pathologist, identified the associated pathogen as Calonectria pteridis.  Then on May 23, 2016, C. pteridis was detected again in a different shipment of majesty palm plants destined to the same nursery in San Luis Obispo.  In both detections, the pathogen was assigned a temporary Q rating by the CDFA and consequently, all infected plant materials were destroyed. The risk of infestation of C. pteridis in California is evaluated and a permanent rating is proposed here.

History & Status:

Background:  Calonectria pteridis is the sexual (telemorph) stage of the fungal pathogen, while its asexual (anamorph) stage is Cylindrocladium pteridisCalonectria pteridis causes leaf spot and blight, stalk and root rot diseases in various hosts.  In the continental United States, Calonectria pteridis primarily causes symptoms of leaf spots and blights in palm.  Symptoms are indistinguishable from those caused by three other species in the genus (Yu & Elliot, 2013).  In Brazil, C. pteridis is one of the most common species associated with eucalyptus trees causing Calonectria leaf blight disease (Alfenas et al., 2013). In China, C. pteridis caused serious damage to Serenoa repens – an important medicinal and ornamental garden plant (Yang, et al., 2014).  In the USA, C. pteridis has been found on several hosts including palm from Tennessee, Georgia, Florida, and Hawaii (Uchida, 2004; Farr & Rossman, 2016). Recently, the pathogen was detected in infested majesty palm plants shipped from Florida to California.  The pathogen is widespread especially in subtropical and tropical regions.

Disease cycle:  The disease cycle generally involves the pathogen’s anamorphic or asexual stage resulting in the production of conidia (spores) and telemorphic or sexual stage resulting in perithecia (fruiting structure) and ascospores. Conidia, produced on infected plants are dispersed by insects, tools, gloves, plant handling, wind and splashing water, while ascospores are discharged from fruiting bodies by air currents and splashing water.  Discharged spores land on plant host tissue and germinate and penetrate tissue when leaves are wet or under high relative humidity.  The pathogen grows within the host and after about one week produces conidiophores and conidia.  Perithecia and ascospores are formed on infected tissue (Uchida, 2004; Yu & Elliot, 2013).

Hosts: Calonectria pteridis can attack a number of hosts including ornamentals, forest and environmental trees and shrubs, and few agricultural crops.  In the USA, palms have been reported as the main host attacked by the pathogen.  Hosts include: Arachis hypogaea (peanut), Arachnoides adiantiformis  (syn. Rumohra adiantiformis, Polystichum adiantiformis; leatherleaf fern), Arecastrum romanzoffianum (syn. Sygarus romanzoffiana; queen palm); Asparagus plumosus (asparagus fern), Callistemon citrinus (crimson bottlebrush), C, rigidus (erect bottlebrush), Chamaedorea elegans (syn. Collinia elegans; neanthe bella palm/parlor palm), C. cataractarum (cat palm), Chrysalidocarpus sp. (syn. Dypsis sp.; palm); Cissus rhombifolia (grape ivy), Cocos nucifera (coconut), Crassula sp., C. argentea (jade plant), Dictyosperma album (princess palm), Dracaena marginata (Marginate Dracaena), Drosera sp. (sundews), Dryopteris sp. (woodfern), Elaeis guineensis (African oil palm), Eucalyptus spp.,(eucalyptus), Guzmania wittmackii (bromeliad/Guzmanea), Heliconia bihai (macawflower), Howeia belmoreana, H. forsteriana (kentia palm/curly palm), Laccospadix australasica (Atherton palm), Leucadendron sp., Livistona chinensis (Chinese fan palm), Lupinus sp., (lupine), Mauritia flexuosa (moriche palm), Melaleuca leucadendra (weeping paperback), M. quinquenervia (broad-leaved paperback), Musa sp. (banana), Nephrolepis sp., Nephrolepis exaltata (sword fern), Phoenix canariensis (Canary Island date palm), Pinus sp., P. caribaea (Caribbean pine), P. caribbaea var. hondurensis,  P. oocarpa (Mexican yellow pine), Pouteria dulcifica (syn. Synsepalum dulcificum; miracle fruit/sweet berry), Ravenea rivularis (majesty palm), Rhapis humilis (slender lady palm), Rhododendron obtusum (Hiryu azalea/Kurume azalea), Serenoa repens (saw palmetto), Scolopendrium sp., Solanum tuberosum (potato), Strelitzia reginae (bird of paradise), Tillandsia wagneriana (bromeliad), Washingtonia sp., W. filifera (California or desert fan palm), W. robusta (Mexican fan palm) (Crous et al., 1993; Crous & Wingfield, 1993; Farr & Rossman, 2016; Yu & Elliot, 2013).

Symptoms:  Symptoms caused by Calonectria pteridis in palm begin as flecks of small, water-soaked lesions that develop to irregular shades of gray, yellow, reddish brown, brown, or black.  Newly formed lesions are circular or elliptical, 3-5 mm long, and on enlarging develop a tan or gray center surrounded by a brownish halo. The rachis and petiole may become infected with small flecks and eventually leaves and leaflets dry as the disease progresses and lesions coalesce.  Leaf spots may appear on leaves of all ages, although mature leaves are most susceptible (Yu & Elliot, 2013).

Spread:   Conidia are readily spread by insects, pruning tools, plant handling, air currents, rain or splashing irrigation water, while ascospores can be released from their fruiting bodies and spread by air currents and splashing water (Uchida, 2004; Yu & Elliot, 2013).

Damage Potential:  Leaf spot and blight disease caused by Calonectria pteridis can result in reduced plant growth, quality, and marketablility.  Estimates of yield/crop loss due to this pathogen have not been reported.  However, under nursery controlled environments, production of palms, ferns, eucalyptus, and other ornamental host plants may be at heightened risk for pathogen infection and reduced plant production. Seedling and immature palms without trunks are likely to be most susceptible to this leaf spot disease (Yu & Elliot, 2013).  Infection of outdoor growths of palm and eucalyptus trees require warm and humid to wet climate for disease development.  In Brazil, C. pteridis is one of the most important causal agents of Calonectria leaf blight disease of Eucalyptus spp. and has significantly reduced eucalyptus growth (Alfenas, et al., 2013).  In China, up to 100% incidence of leaf spot disease in Serenoa repens, medicinal plant, often lead to plant death (Yang, et al., 2014).

Worldwide Distribution: Asia: China, India, Malaysia, Singapore; Africa: Cameroon, Ivory Coast, Mauritius, South Africa; Europe: Spain, North America: USA (Florida, Hawaii), West Indies; South America: Brazil, Costa Rica, Martinique, Venezuela (Crous & Wingfield, 1993; Farr & Rossman, 2016).

Official Control: None reported.  Currently, Calonectria pteridis is a quarantine, actionable pathogen with a Q rating in California.

California Distribution: Calonectria pteridis is not known to be established in California.  Diseased plants detected in a San Luis Obispo nursery were destroyed (see “Initiating Event).

California Interceptions There have been two interceptions of Calonectria pteridis- infested Ravenea rivularis (majesty palm) plants that originated in Florida (see ‘Initiating Event’).

The risk Calonectria pteridis would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2):  Calonectria pteridis requires humid, wet, rainy and warm climates to infect plants and develop.  Therefore, the pathogen may only be able to establish in limited parts of California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

High (3) has a wide host range.

Risk is High (3): Calonectria pteridis has a very wide host range and can attack a number of diverse hosts including ornamentals, forest and environmental trees and shrubs, and few agricultural crops.  In the USA, palms have been reported as the main host attacked by the pathogen.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

High (3) has both high reproduction and dispersal potential.

Risk is High (3):  The pathogen has high reproductive potential.  Conidia and ascospores are transmitted by wind, wind-driven rain and splashing irrigation water, cultivation tools, and plant handling.  However conidial germination and plant infection require long, wet periods.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2): Infections of Calonectria pteridis could lower crop value and cause loss of markets.  Under controlled wet and warm environments, nursery productions of palms and other ornamental host plants may be at particular risk for pathogen infection and reduced plant production.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  Under conducive climate for development, the pathogen could significantly impact cultural practices or home garden plantings.  Its overall impact on California’s environment is assessed as ‘medium’. 

Consequences of Introduction to California for Calonectria pteridis:

Add up the total score and include it here. (Score)

-Low = 5-8 points

Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Calonectria pteridis to California = (12).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not established (0):  Interceptions of Calonectria pteridis-infected nursery plants were destroyed and therefore, the pathogen is not considered established in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

 Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 12.


Periodic surveys and/or subsequent detection may confirm the presence/absence of C. pteridis in commercial and private production regions within California.  Subsequent results may alter the herein proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Calonectria pteridis is B.


Alfenas, R. F., O. L. Pereira, R. G. Frietas, C. S. Freitas, M. A. D. Dita, and A. C. Alfenas.  2013.  Mass spore production and inoculations of Calonectria pteridis on Eucalyptus spp. under different environmental conditions.   Tropical Plant Pathology, 38:406-413.

Crous, P. W., M. J. Wingfield, and A. C. Alfenas.  1993. Additions to Calonectria.  Mycotaxon 46:217-234.

Crous, P. W., and M. J. Wingfield. 1993.  Calonectria pteridis.  IMI Descriptions of Fungi and Bacteria. No. 116 pp. Sheet 1153.

Farr, D.F., & A. Y. Rossman.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from

Uchida, J. Y.  2004.  Calonectria leaf spot (Cylindrocladium leaf spot).  In ‘Compendium of Ornamental Palm Disease and Disorders’ Eds. M. L. Elliott, T. K. Broschat, J. Y. Uchida, and G. W. Simone.  The American Phytopathological Society, pgs. 12-14.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.

Yang, W., L. Zheng, C. Wang, and C. -P. Xie.  2014.  The first report of Calonectria pteridis causing a leaf spot disease on Serenoa repens in China. Plant Disease. 986: 854.

Yu, J. and M. L. Elliott.  2013.  Calonectria (Cylindrocladium) leaf spot of palm.  University of Florida Institute of Food and Agricultural Sciences.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: (916) 262-1110,[@]

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Pest Rating: B

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