Cercospora insulana Sacc. 1915

California Pest Rating for

Cercospora insulana Sacc. 1915

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

On May 11, 2018 a postal shipment of statice dried flowers showing symptoms of leaf spots was intercepted by the CDFA at a Federal Express (FedEx) office. The shipment was destined to a private owner in Alameda County and had originated in Hawaii. A sample of the symptomatic flowers was sent to the CDFA Plant Pathology Lab for disease diagnoses. On May 17, 2018 Cheryl Blomquist, CDFA plant pathologist, identified the fungus, Cercospora insulana associated with the leaf spots. The present status and rating of C. insulana is reevaluated here.

History & Status:

Background: Cercospora insulana is a fungal plant pathogen in the Mycosphaerellaceae family, that causes leaf spot of statice and other host plants.

The pathogen is globally widespread. In the USA, Cercospora insulana has only been reported from Florida and California (Farr & Rossman, 2018). In California, prior to its most recent detection, the pathogen has been reported on Armeria sp. and Limonium spp. in northern and southern coastal region of California (French, 1989).

Disease cycle: In general, plants infected with Cercospora species produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively. Conidia are easily detached and blown by wind often over long distances. On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host. Substomatal stroma (compact mycelial structure) may form from which conidiophores develop. Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates. High relative humidity is necessary for conidial germination and plant infection. The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).

Dispersal and spread: Dispersal and spread: air-currents, infected nursery plants, infected leaves, seeds (Agrios, 2005).

Hosts: Armeria sp., A. maritima (thrift seapink), Limonium sp., L. bonducellii (Algerian statice), L. californicum (California sea lavender/marsh rosemary), L. gmelinii (syn. Statice gmelinii; Siberian statice), L. sinuatum (syn. Statice sinuata; statice/wavyleaf sea lavender), L. vulgare (common sea lavender) (CABI, 2018; French, 1989); Nerium indicum (Indian oleander) (XueWen et al., 2017)

Symptoms: Leaf spot symptoms caused by Cercospora insulana in field-grown statice were reported from Italy as circular, brown lesions with a darker edge, 3-6 mm in diameter and surrounded by an orange or reddish halo. Old lesions enlarged and coalesced, causing yellowing and senescence of leaves. Heavy infections resulted in severe defoliation and retarded growth or death in panicles. Lesions were also present on the wings of the flower scapes, while scapes proper were not involved (Nicoletti et al., 2003).

Damage Potential: Quantitative losses due to Cercospora insulana have not been reported. If left uncontrolled, leaf spotting may lead to disease outbreaks under favorable conditions, wherein photosynthetic areas can be reduced. Heavy infections may result in severe defoliation, retarded plant growth and death of flowers in statice, and likely, in other ornamental host plants. Nursery productions of ornamental hosts under controlled and conducive conditions for pathogen development would also be of concern in California. However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005). Furthermore, fungicide applications and sanitary measures including the use of clean seed have been used to successfully control Cercospora diseases (Agrios, 2005).

Worldwide Distribution: Asia: China (XueWen et al., 2017), India, Myanmar; Africa: Kenya, Malta, South Africa, Zimbabwe; Europe: Caucasus, Italy, Portugal, Russia: North America: USA (California, Florida), Haiti; Oceania: Australia, New Zealand (Farr & Rossman, 2018)

Official Control: Presently, Cercospora insulana is on the ‘Harmful Organism’ list for Brazil, Colombia, Ecuador and Israel (USDA PCIT, 2018).

California Distribution: Cercospora insulana is distributed in northern and southern coastal areas of the State (French, 1989).

California Interceptions: To date, the recent detection of C. insulana (see ‘initiating event’) has been the only interception reported.

The risk Cercospora insulana would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Cercospora insulana has only been detected in northern and southern coastal regions in California. These limited regions provide adequate moisture that favor development of the pathogen in host plants like statice.

Evaluate if the pest would have suitable hosts and climate to establish in California. Score: 2

– 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.

2) Known Pest Host Range: The known host range is limited to statice, thrift seapink and Indian oleander in the genera Limonium, Armeria and Neria.

Evaluate the host range of the pest. Score: 1

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Cercospora insulana has high reproductive potential resulting in the successive production of conidia which primarily depend on air currents, infected plants and seed for dispersal and spread.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– 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.

4) Economic Impact: Quantitative losses due to Cercospora insulana have not been reported. However, for nurseries particularly, infected host plants with leaf spots could result in lowered value resulting in use of fungicidal treatments thereby increasing production costs, and loss of markets.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: B, C

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.

Economic Impact Score: 2

– 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.

5) Environmental Impact: Home garden plantings of statice species may be impacted if the pathogen was to establish under favorable environmental conditions and in the absence of adequate disease control. The pathogen has not been detected in oleander in California.

Evaluate the environmental impact of the pest on California using the criteria below.

Environment Impact: E

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.

Environmental Impact Score: 2

– 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.

**Consequences of Introduction to California for Cercospora insulana:**

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 = 10

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.

Evaluation is ‘Medium’ in California.

Score: (-2)

-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.

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 = 8

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cercospora insulana is to continue as C.

References:

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

Farr, D.F., & A. Y. Rossman. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved May 18, 2018, from http://nt.ars-grin.gov/fungaldatabases/

French, A. M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Nicoletti, R., F. Raimo, C. Pasini, and F. D’Aquila. 2003. Occurrence of Cercospora insulana on statice (Limonium sinuatum) in Italy. Plant Pathology 52: 418. DOI: 10.1046/j.1365-3059.2003.00840.x

USDA PCIT. 2018. USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved May 18, 2018. 12:45:06 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

XueWen, X., Z. Qian and G. YingLan. 2017. New records of Cercospora and Pseudocercospora in China. Mycosystema 36: 1164-1167.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-738-6693, plant.health[@]cdfa.ca.gov.

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