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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: Effects of Almond Leaf Scorch Disease on Yield and Tree Vitality

Author
item Sisterson, Mark

Submitted to: Almond Industry Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 19, 2007
Publication Date: December 5, 2007
Citation: Sisterson, M.S. 2007. Effects of Almond Leaf Scorch Disease on Yield and Tree Vitality. In: Proceedings of the 35th Annual Almond Industry Conference, December 5-6, 2007, Modesto, California. p. 138-140.

Interpretive Summary: Almond leaf scorch disease (ALS) is present in orchards throughout California, but incidence is typically low. As there are no effective techniques for preventing trees from becoming infected, growers must decide to keep or replace infected trees. Research suggests that tree-to-tree spread of the pathogen which causes ALS is rare. Thus, the decision to replace infected trees should focus on lost productivity. To address this issue, the yields of ALS-affected trees were compared to unaffected trees for the cultivars Sonora and Nonpareil. Yields of ALS-affected Sonora trees were 40 percent lower than unaffected Sonora trees, whereas yields of ALS-affected Nonpareil were 20 percent lower than unaffected Nonpareil trees. Due to the reduced productivity of ALS-affected trees, it has been hypothesized that healthy trees which are next to infected trees may produce greater yields than healthy trees which are next to other healthy trees. If true, such compensatory effects could negate losses due to ALS. We tested this hypothesis for the cultivars Sonora and Nonpareil. Mean yields of healthy trees which were next to infected trees were ~9 percent greater than those of healthy trees which were next to other healthy trees, but this effect was not significant for either cultivar. The information collected in this study will be used to develop a model that will help growers determine when replacing infected trees will increase returns.

Technical Abstract: Almond leaf scorch disease (ALS) has been present in California for more than 60 years. The disease is present in orchards throughout the state, but usually affects only a small proportion of trees and large increases in the number of infected trees within orchards between years is typically not observed. A major question for growers is whether or not to remove infected trees. As tree-to-tree spread of ALS appears to be rare, the decision to remove infected trees should focus on productivity. To address this issue we compared the yields of ALS-affected and unaffected trees for the cultivars Sonora and Nonpareil. Averaged across sites and years, ALS-affected Sonora trees produced 40% fewer kg of kernel relative to unaffected Sonora trees. Averaged over years, ALS-affected trees produced 20% fewer kg of kernel relative to unaffected trees. Due to the reduced productivity of ALS-affected trees, it has been hypothesized that healthy trees which are next to infected trees may produce greater yields than healthy trees which are next to other healthy trees. If true, such compensatory effects could negate losses due to ALS. We tested this hypothesis for the cultivars Sonora and Nonpareil. Averaged over three sites, healthy Sonora trees which were next to ALS-affected Sonora trees produced 10% more kg’s of kernel than healthy trees which were next to other healthy trees, although this effect was not significant. For the cultivar Nonpareil, we found that healthy trees next to ALS-affected trees produced 8% more kg’s of kernel than healthy trees next to other healthy trees, although this effect was also not significant. After one year of testing it appears that compensatory effects are minimal. The information collected in this study will be used to parameterize a model that will aid in determining when the economic benefits of replacing an infected tree exceed that of leaving the infected tree in place.

Last Modified: 4/16/2014
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