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United States Department of Agriculture

Agricultural Research Service

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

Authors
item Sisterson, Mark
item Chen, Jianchi
item Civerolo, Edwin
item Ledbetter, Craig
item Groves, Russell - UNIVERSITY OF WISCONSIN

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 5, 2007
Publication Date: February 1, 2008
Citation: Sisterson, M.S., Chen, J., Civerolo, E.L., Ledbetter, C.A., Groves, R.L. 2008. Effects of Almond Leaf Scorch Disease on Almond Yield and Implications for Management. Plant Disease 92:409-414.

Interpretive Summary: 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. To help growers determine if they should replace or keep infected trees, the yield and vitality of ALS-affected and unaffected almond were compared. Two cultivars were examined, Sonora and Nonpareil. Yields of ALS-affected trees were lower than those of unaffected trees for both cultivars. A simple economic model was used to evaluate the conditions under which replanting infected trees would increase returns. Based on the model, orchard age, the degree of yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to replace ALS-affected trees. Results of this project will have a direct impact on growers by providing detailed information on the effects of ALS on almond yield.

Technical 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 the cultivars Sonora and Nonpareil. The cultivar Sonora was examined at three sites over three years and the cultivar Nonpareil was examined at one site over two years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than that of Nonpareil. Yields of infected trees did not decline incrementally over years; rather they fluctuated similar 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 should incrementally decline and infected trees should eventually die. A simple economic model was developed to determine the 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.

Last Modified: 12/18/2014