APS Abstracts of Presentations

Occurrence of esca in California vineyards and association with environmental conditions. A. ESKALEN, S. R. Latham, and W. D. Gubler. Dept. of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 93:S24. Publication no. P-2003-0173-AMA.

Esca has been a problem on both wine and table grape varieties in California for over 70 years. The erratic nature of symptoms in infected vineyards has resulted in sporadic research efforts to understand disease biology. Symptom expression of esca in vineyards less than 10 years of age has been rare until recently, when we observed esca symptoms in many vineyards less than 3 years of age. The fungus Phaeomoniella chlamydospora has been identified as the primary causal agent of esca in California vineyards with species of Phaeoacremonium also playing a role. Data show that weather conditions appear to be roughly correlated with esca occurrence. In years with higher than normal rainfall and summer temperatures, fruit and foliar symptoms of the esca were abundant. Spore trapping data and some speculation seemed to indicate that symptom expression occurs in the year when new infections occur. However, vineyard surveys over the past two years, indicate that symptom expression may not occur until the year following infection. Correlations between symptom expression, rainfall and temperature will be presented.