Puccinia crepidis-japonicae (Lindr.) Dietel (Rust)

California Pest Rating for
Puccinia crepidis-japonicae (Lindr.) Dietel
Pest Rating: D 


Initiating Event:

Recently, the USDA NPAG (New Pest Advisory Group) reported and evaluated the detection of Puccinia crepidis-japonicae in Gainesville, Florida, thereby, marking the first record of this pathogen in the USA.  Subsequently, the risk and consequences of its introduction to, and establishment in California is assessed here and a permanent rating is proposed.

History & Status:

Background:  In February 2015, the fungal rust pathogen, Puccinia crepidis-japonicae, was discovered on the exotic weed Youngia japonica (oriental false Hawksbeard) in Florida (USDA NPAG, 2015).  The pathogen primarily attacks weed plants.  While P. crepidis-japonicae is reported to attack plant genus Prenanthes, the host Y. japonica was originally described under the genus name Prenanthes japonica. Therefore, it is likely that the pathogen may be limited to the host belonging to Youngia spp.  This common host, Youngia spp., is present in southern California, and Y. japonica grows there as a garden weed at the edge of lawns and planting beds.

Puccinia crepidis-japonicae has not been reported from California. However, there is a very early record of a different species belonging to the same group, namely, P. crepidis-acuminatae P. Syd. & Syd., which was detected on naked-stem Hawksbeard, (Crepis runcinata which is now a synonym of Youngia runcinata) and tapertip Hawksbeard (Crepis acuminata, synonym of Y. acuminata) in California (Blasdale, W. C. 1919: A preliminary list of the Uredinales of California. University of California Publications in Botany, 7:101-157).

Puccinia crepidis-japonicae is not considered an economically damaging pathogen as it is associated with non-economically important plants. Pereira et al., 2002 suggested that P. crepidis-japonicae may play a significant role as a biocontrol agent against its weed host.  In Florida, the possibility of using this exotic rust against the exotic host, Youngia japonica, is being considered (USDA NPAG, 2015).  However, it is not known if the pathogen kills its host since it needs the latter in order to live as a parasite.

Disease cycle:  The complete life cycle and climate requirements for disease development for Puccinia crepidis-japonicae are not known.  In general, rust pathogens require living host plants to complete a life cycle.  The life cycle may be completed in one or two hosts – and this is not known for P. crepidis-japonicae. Rusts attack only certain genera or varieties of plants.  This appears to be the case for P. crepidis-japonicae. Rusts may have a short cycle (microcyclic) producing only two different spores: teliospores and basidiospores, or a long cycle (macrocyclic) producing five different spores: teliospores, basidiospores, spermatia, aeciospores, and urediniospores. Only urediniospores and teliospores are reported for P. crepidis-japonicae, so this pathogen may be macrocyclic. Urediniospores infect host plants and can rapidly spread to cause new and multiple infections of host plants (Agrios, 2005).

Dispersal and spread:  The pathogen is spread from plant to plant mainly by windblown spores.  Urediniospores can be transported over several hundred kilometers by strong winds and washed down by rain to available hosts.  Insects, animals, humans, and rain may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Hosts: Asteraceae – Prenanthes sp. (rattlesnake root), Youngia fusca, Y. japonica (oriental false Hawksbeard), Y. tenuifolia, Y. japonica (originally cited as Crepis japonica which is now a synonym of Y. japonica) (Farr & Rossman, 2015).

Symptoms and damage potentialPuccinia crepidis-japonicae primarily attacks weed plants (e.g., Youngia japonica) producing dark brown, irregularly oval-shaped leaf lesions containing urediniospores (Pereira et al., 2002).

Worldwide Distribution: Asia: China, Korea, Japan, Yoron Islands; North America: United States; Oceania: Australia, New Caledonia; South America: Brazil (Farr & Rossman, 2015; USDA NPAG, 2015; Pereira, et al., 2002; Zhuang, 1989).

In the United States, it has only been reported from Florida (USDA NPAG, 2015).

Official Control: Puccinia crepidis-japonicae is not listed as a harmful organism by any country (PCIT, 2015).  No official control of this pathogen is reported.

California Distribution: Puccinia crepidis-japonicae is not present in California.

California Interceptions:  None reported.

The risk Puccinia crepidis-japonicae Rust 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 Low (1):  If introduced, Puccinia crepidis-japonicae is likely to establish under favorable environmental conditions in limited areas within southern California where its common host, Youngia spp. is present.

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 Low (1): The host range is limited to weed plants in the genus Youngia spp. in the family Asteraceae. 

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): Puccinia crepidis-japonicae has both high reproduction and dispersal potential through the production of abundant, infective urediniospores and the ease of their spread by winds, insects, animals, humans, and rain to non-infected host plants.  

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 Low (1): Puccinia crepidis-japonicae is not considered an economically damaging pathogen as it is associated with non-economically important plants or weeds.

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 Low (1): None.

Consequences of Introduction to California for Puccinia crepidis-japonicae Rust:

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 to California = 7

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).

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 = 7.


Details of the life cycle and complete host range are unknown.  However, it is unlikely this knowledge will significantly alter the proposed rating for Puccinia crepidis-japonicae.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Puccinia crepidis-japonicae Rust is D.


Agrios, G. N.  2005.  Plant Pathology Fifth Edition.  Elsevier Academic Press, USA.  922 p.

Farr, D.F., & Rossman, A.Y. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved August 31, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Pereira, O. L., J. R. P. Cavallazzi and R. W. Barreto.  2002.  First report of Uredo crepidis-japonicae and Septoria crepidis on Crepis japonica in Brazil. Fitopathológicas Brasileira 27 (3):319.

USDA NPAG.  2015.  NPAG report Puccinia crepidis-japonicae (Lindr.) Dietel: Rust.  USDA/APHIS/ PPQ/CPHST/PERAL NPAG Report 20150615.docx. 6 pg.

Zhuang, J. Y. 1989. Rust fungi from the desert of northern Xinjiang. Acta Mycologica Sinica 8(4):259-269.

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, plant.health[@]cdfa.ca.gov.

Comment Period:

The 45-day comment period opened on Monday, October 12, 2015 and closed on November 26, 2015.

Pest Rating: D

Posted by ls