Summer 2014: First detection of Colletotrichum cymbidiicola in California and Water Supply Update

Regional Report for San Diego and Riverside Counties by James A. Bethke

First detection of Colletotrichum cymbidiicola in California

On a recent nursery inspection, the San Diego County plant pathologist noticed black spots on some leaves in a greenhouse full of cymbidium orchids and thought it was a common foliar infection. You can walk into most orchid greenhouses and see black spots on leaves, especially the older leaves. Following procedure, the plant pathologist sent the samples to a diagnostic lab and the disease was determined to be caused by Colletotrichum cymbidiicola. This was the first detection in North America of this fungus. The infected plants sampled in San Diego County originated in Santa Clara County and subsequently the pathogen was found there too.

The genus Colletotrichum includes a number of plant pathogens of major importance, causing diseases of a wide variety of woody and herbaceous plants, and was recently voted the eighth most important group of plant pathogenic fungi in the world, based on perceived scientific and economic importance (Cannon et al. 2012, Dean et al. 2012). It is primarily found in tropical and subtropical regions. Strains of Colletotrichum often belong to aggregates of species that can be difficult or impossible to distinguish morphologically. The fungus, Colletotrichum cymbidiicola, is one of a group of related Colletotrichum that belongs to an aggregated species (C. boninense) and is associated with orchids, appearing host specific at plant genus level (Damm et al. 2012).

As plant pathogens, Colletotrichum species primarily cause anthracnose diseases. On cymbidium orchids, anthracnose is characterized by black spots on lower leaves and premature loss of infected leaves. Under humid conditions tiny black dots that look like lumps of coal emerge from the diseased tissue in a circular pattern. Spores are spread by water so keep water off of the leaves. Additionally, remove infected leaves, handle infected plants as little as possible and reduce crowding to ensure good air circulation. These measures will reduce disease expression and spread.

At the time of this writing, C. cymbidiicola has been given a Q rating by CDFA, which means the fungus is a potentially destructive organism of limited distribution in California and control measures must be taken. A delimitation survey is underway, and if it is found widespread in California, there is a chance it could receive a different rating. We will have to wait and see.

References

Cannon PF, Damm U, Johnston PR, Weir BS. 2012. Colletotrichum – current status and future directions. In: Damm U, Cannon PF, Crous PW (eds). Colletotrichum: Complex Species or Species Complexes? (Stud. Mycol. Vol 73). Utrecht, The Netherlands. p 181–213. http://www.cbs.knaw.nl/publications/sim73.pdf.

Damm U, Cannon PF, Woudenberg JHC, Johnston PR, Weir BS, Tan YP, Shivas RG, Crous PW. 2012. The Colletotrichum boninense species complex. In: Damm U, Cannon PF, Crous PW (eds). Colletotrichum: Complex Species or Species Complexes? (Stud. Mycol. Vol 73). Utrecht, The Netherlands. p 1–36. http://www.cbs.knaw.nl/publications/sim73.pdf.

Dean R, Van Kan JAL, Pretorius ZA, Hammond-Kosack KE, Di Pietro A. 2012. The Top 10 fungal pathogens in molecular plant pathology. Molecular Plant Pathology 13: 414–430.

Water supply update

Following two straight dry years and an extraordinarily dry start to a third, the San Diego County Water Authority’s Board of Directors activated its Water Shortage and Drought Response Plan on February 13. The Board also declared the region to be in a Drought Watch condition, which calls for increasing voluntary water conservation efforts by homes and businesses.

However, although mandatory supply cuts were imposed on the region by the Metropolitan Water District (MWD) between July 2009 and April 2011, the Water Authority is not expecting any cutbacks to its imported water supply sources this year. San Diego County is being protected from immediate impacts of the drought by several factors, including significant investments in diversification of the region’s water supplies and an effort to increase water storage levels. In addition, San Diego County residents, businesses and agricultural water users have done a great job using water more efficiently (per capita water use fell 27 percent between 2007 and 2013). By developing new local and imported supplies and boosting conservation, the San Diego region has reduced its reliance on MWD supplies to 46%, a reduction of 49% from 1991.

It’s with great anticipation that the region will begin purchasing up to 56,000 acre-feet of desalinated seawater annually from the new Carlsbad Desalination Project. This will further increase local water supplies and reduce the reliance on MWD supplies.

While recommended water use practices or restrictions may vary by local agency, the San Diego County Water Authority recommends typical conservation steps during
the Drought Watch condition. For more information on the Drought Watch Plan, water conservation practices and the region’s water supplies, see the San Diego County Water Authority website (http://www.sdcwa.org/) and the following links:

http://www.sdcwa.org/sites/default/files/watersupplyoutlook-fs.pdf,

http://www.sdcwa.org/drought-response.

UC Cooperative Extension is also a resource on water conservation measures. For example, UCNFA held a workshop, “Irrigation Management Efficiency in Nurseries” in San Marcos on June 25. The ongoing UC Cooperative Extension, San Diego County Water Schools (http://ucanr.edu/sites/agwaterquality/) include management practices that reduce runoff and conserve water.

James A. Bethke
Farm Advisor, Nurseries and Floriculture
UC Cooperative Extension San Diego, North County Office
151 E. Carmel St., San Marcos, CA 92078
(760) 752-4715 phone; (760) 752-4725 fax
jabethke@ucanr.edu 
http://cesandiego.ucdavis.edu/