California Pest Rating for
Phyllosticta yuccae Bissett 1986
Pest Rating: C
PEST RATING PROFILE
On June 17, 2016 Yucca elephantipes (Adam’s needle) plants exhibiting leaf spot symptoms were intercepted at a nursery in San Diego County by San Diego County officials. The shipment had originated in Florida. Samples of symptomatic leaves were collected by the County and sent to the CDFA Plant Pathology Laboratory for disease diagnosis. On July 17, 2016 Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Phyllosticta yuccae, as the cause for the disease. The pathogen has not been previously reported in California and therefore, was assigned a temporary Q rating. Subsequent action taken by CDFA resulted in prevention of the shipment from introduction to California. The risk of infestation of Phyllosticta yuccae in California is evaluated and a permanent rating is herein proposed.
History & Status:
Background: Phyllosticta yuccae causes leaf blotch disease in Yucca plants.
Disease cycle: It is likely that Phyllosticta yuccae has a similar life cycle to that of other Phyllosticta species and overwinters as conidia (asexual spores) in pycnidia (asexual fruiting structures) and ascospores (sexual spores) in perithecia (sexual fruiting structures) in infected plant leaf debris. Conidia and ascospores are only released when the fruiting structures become thoroughly wet. Conidia are exuded from pycnidia in mucoid mass and are washed down or splashed away by rain or overhead irrigation water. Ascospores are shot out forcibly from perithecia and carried by air currents. On landing on host leaf surfaces, conidia or ascospores are germinate and infect plant tissue of young leaves. Pycnidia are produced within lesions and provide conidia for secondary infections of plants (Agrios, 2005).
Dispersal and spread: rain/water splash, air currents, infected plant material and debris.
Hosts: Yucca sp., Y. aloifolia, Y. elephantipes, Y. filamentosa (Farr & Rossman, 2016).
Symptoms: Phyllosticta yuccae infections result in production of leaf spots in Yucca plants. Initial symptoms include dark brown, elliptical, and scattered lesions which later become grey at the center with a reddish brown margin, irregular and coalesced (Silva et al., 2013).
Disease Potential: Symptomatic Yucca plants infected with Phyllosticta yuccae may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California. The disease could negatively impact value and marketability of nursery-grown Yucca plants.
Worldwide Distribution: Asia: Iran; Caribbean: Dominican Republic; North America: Canada, USA (Florida), Guatemala; South America: Brazil; Oceania: New Zealand (Farr & Rossman, 2016; Silva et al., 2013).
Official Control: Currently, Phyllosticta yuccae has a temporary Q rating in California.
California Distribution: Phyllosticta yuccae is not established in California.
California Interceptions: Phyllosticta yuccae was detected once in a shipment of Yucca elephantipes plants from Florida and destined to a San Diego nursery.
The risk Phyllosticta yuccae 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): Yucca plants. grow naturally under dry conditions in southern California. Under those natural conditions, Phyllosticta yuccae may not receive adequate wet conditions for infection and spread. However, certain species of the host plant may be grown as residential and commercial landscape ornamentals in coastal regions of southern and central California under favorable environments for disease development.
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 Yucca spp.
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 Medium (2): Phyllosticta yuccae has high reproductive potential, however, the dispersal of spores from fruiting structures is dependent on wet conditions.
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): Nursery grown Yucca plants infected with Phyllosticta yuccae and exhibiting leaf blotch/spot symptoms could lower crop value and marketability.
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 favorable conditions for disease development, Phyllosticta yuccae may significantly impact ornamental plantings of commercially and home grown Yucca plants.
Consequences of Introduction to California for Phyllosticta yuccae:
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 = 8 (Low).
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). Phyllosticta yuccae is not established in California.
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 (Low).
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for Phyllosticta yuccae is C.
Agrios, G. N. 2005. Plant Pathology (Fifth Edition). Elsevier Academic Press, USA. 922 p.
Farr, D. F. and A. Y. Rossman. 2016. Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.
Ingram, S. 2008. Cacti, Agaves and Yuccas of California and Nevada. Pacific Horticulture, 69 (3): http://www.pacifichorticulture.org/articles/cacti-agaves-and-yuccas-of-california-and-nevada/
Silva, A.D.A., Pinho, D.B., Jr., Hora, B.T., and Pereira, O.L. 2013. First Report of Leaf Spot Caused by Phyllosticta yuccae on Yucca filamentosa in Brazil. Plant Disease 97: 1257.
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.
PEST RATING: C
Posted by ls