Host-specific strain of Stemphylium causes leaf spot disease of California spinach
California Agriculture 55(5):31-34.
The California spinach industry has grown dramatically over the past few decades; it now supplies well over 100,000 tons of various high-quality products to consumers. But a new foliar disease. Stemphylium leaf spot, can reduce spinach quality. After identifying this disease, we determined that the pathogen may also be a new, distinct strain of the fungus that is specific to spinach. Inoculation experiments demonstrated that numerous spinach lines are susceptible, including new downy mildew-resistant cultivars. Diagnosing this disease can be difficult because its symptoms often resemble damage from agrochemicals. Growers and pest control advisors should become familiar with the symptoms of the various foliar spinach diseases that occur in California because consumers of this crop tolerate only a small level of leaf spots and defects.
S.T. Koike is Plant Pathology Farm Advisor, UC Cooperative Extension, Monterey and Santa Cruz counties; D.M. Henderson is Agricultural Aide, UC Cooperative Extension, Monterey and Santa Cruz counties; E.E. Butler is Professor Emeritus, Department of Plant Pathology, UC Davis;
The authors thank Ted Angell, Marvin Borzini, Mildred Butler, Jim C. Correll, Tom Galdos, Dave G. Gilchrist, Teo G. Gonzales, David Haviland, Tom Hussar, Sharon Lanini, Teddy Morelock, Scott Nishihara and Dan Putnam. The first author thanks J.D. MacDonald, R.M. Bostock and the UC Davis Department of Plant Pathology for the use of department facilities. This research was supported in part by grants from UC Cooperative Extension Assembly Council Fellowship for Advanced Studies (1997) and the Department of Agronomy Milton D. and Mary M. Miller Plant Science Award for 1997–1998, UC Davis.