Link to home

Effects of Almond Leaf Scorch Disease on Almond Yield: Implications for Management

March 2008 , Volume 92 , Number  3
Pages  409 - 414

Mark S. Sisterson and Jianchi Chen, United States Department of Agriculture--Agricultural Research Service (USDA-ARS), San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93611; Mario A. Viveros, University of California Cooperative Extension, Bakersfield 93307; Edwin L. Civerolo and Craig Ledbetter, USDA-ARS, San Joaquin Valley Agricultural Sciences Center; and Russell L. Groves, Department of Entomology, University of Wisconsin, Madison 53706



Go to article:
Accepted for publication 5 October 2007.
ABSTRACT

Almond leaf scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees.



The American Phytopathological Society, 2008