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United States Department of Agriculture

Agricultural Research Service

Research Project: EPIDEMIOLOGY AND MANAGEMENT OF XYLELLA FASTIDIOSA (XF) AND OTHER EXOTIC AND INVASIVE DISEASES AND INSECT PESTS

Location: Crop Diseases, Pests and Genetics

Title: Long term evaluation of the effects of almond leaf scorch disease on orchard productivity

Authors
item Sisterson, Mark
item Daane, Kent - UC BERKELEY

Submitted to: Almond Industry Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 29, 2008
Publication Date: December 10, 2008
Citation: Sisterson, M.S., Daane, K. 2008. Long term evaluation of the effects of almond leaf scorch disease on orchard productivity. In: Proceedings of the 36th Annual Almond Industry Conference, December 10-11, 2008, Modesto, California. p. 164-166.

Interpretive Summary: Almond leaf scorch (ALS) disease has been a chronic problem for almond growers in California’s Central Valley for more than 60 years. This disease is caused by the bacterium Xylella fastidiosa. The pathogen is vectored by xylem feeding insects and in California’s Central Valley the green sharpshooter is thought to be the most important vector. Currently, there are no effective management strategies to prevent almond trees from becoming infected. Consequently, growers must decide to keep or remove ALS-affected trees. The decision to keep or remove ALS-affected trees is a function of two components: risk of infected trees serving as a source of inoculum and yield losses due to infection. To determine whether ALS-affected trees serve as a source of inoculum, two almond orchards were surveyed in 2004 and re-surveyed in 2008, to determine extent of pathogen spread. Screening of samples collected in 2008 is not yet complete. In regards to the second component, yields of ALS-affected and unaffected trees were compared over the last five years. This study has consistently shown that ALS-affected trees produce 40 percent and 20 percent fewer kg of kernel than unaffected trees for the cultivars Sonora and Nonpareil, respectively. Collectively, the data will facilitate grower’s decisions regarding removal of ALS-affected trees.

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 also causes several other important plant diseases, most notably Pierce’s disease of grapes. With the exception of planting resistant cultivars, there are no effective management strategies that prevent almond trees from becoming infected. Consequently, growers must decide to keep or remove ALS-affected trees. The decision to keep or remove ALS-affected trees is a function of two components: risk of infected trees serving as sources for in-field, secondary pathogen spread and yield losses due to infection. To determine risk of secondary pathogen spread, two almond orchards were surveyed in 2004 and re-surveyed in 2008. Screening of samples collected in 2008 is not yet complete. Once completed, the spatial distribution of ALS-affected trees in 2004 will be compared to that in 2008 to assess the extent of pathogen secondary spread. With respect to the second component, yields of almond leaf scorch-affected and unaffected trees were compared over the last five years. This study has consistently shown that ALS-affected trees produce 40% and 20% fewer kg of kernel than unaffected trees for the cultivars Sonora and Nonpareil, respectively.

Last Modified: 9/1/2014
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