ARS | Publication request: Epidemiology of almond leaf scorch disease in the San Joaquin Valley of California

Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: March 16, 2010
Publication Date: June 2, 2010
Citation: Sisterson, M.S., Chen, J., Daane, K., Groves, R., Higbee, B., Ledbetter, C.A. 2010. Epidemiology of almond leaf scorch disease in the San Joaquin Valley of California. Phytopathology. 100:S119.

Technical Abstract: Almond leaf scorch (ALS) disease has been present in California for more than 60 years. This disease is caused by the bacterium Xylella fastidiosa, which causes several other important plant diseases, including Pierce’s disease of grapes. The epidemiology of ALS in the San Joaquin Valley of California was investigated to determine: 1) effects of ALS on tree yield and longevity, 2) regional incidence, and 3) disease progress curves in select orchards. Yields of ALS-affected trees were significantly lower than yields of unaffected trees. Yield loss varied with cultivar and tree death due to ALS over a 5-6 year period was rare. Almond leaf scorch disease was common in the San Joaquin Valley and at least one infected tree was found in 34 of 61 (56%) orchards containing the cultivar Sonora. Incidence in surveyed orchards was typically low (<2%). Multi-year surveys in two severely affected orchards found that incidence varied with cultivar and appeared to increase at a steady rate. For example, in one orchard incidence in the cultivar Sonora increased from 5.8% in 2003 to 8.5% in 2009. Incidence in the cultivar Nonpareil in the same orchard was lower with 1.3% of trees affected in 2003 and 2.7% of trees affected in 2009. The results indicate that ALS is present in orchards throughout the San Joaquin Valley, but that incidence and yield effects vary with cultivar.