Monitoring of ascospore density of Erysiphe necator in the air in relation to weather factors and powdery mildew development

Holb, Imre and Füzi, I. (2016) Monitoring of ascospore density of Erysiphe necator in the air in relation to weather factors and powdery mildew development. EUROPEAN JOURNAL OF PLANT PATHOLOGY, 144 (4). pp. 751-762. ISSN 0929-1873

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Abstract

In a 6-year Hungarian study, ascospore den- sity of Erysiphe necator in the air was monitored and related to three weather variables (temperature, relative humidity, and rainfall) and powdery mildew disease progress in two commercial vineyards. Temporal pattern in aerial density was also quantified. In total, 71 asco- spore trapping periods were detected over the 6-year period from early April until end June. Across all years, 6.6 % of the total ascospores (0.5 % mean ascospore percent per day) were caught between the initiation of sampling in April and bud break, 62.2 % (1.6 %) from bud break to bloom, and 31.2 % (0.3 %) between bloom and the conclusion of sampling at the end of June. Hourly proportions of ascospores caught did not reveal diurnal patterns of spore release. All three weather fac- tors (in the order of rainfall, relative humidity and tem- perature) correlated significantly with mean ascospore catches in each year. Mean hourly rainfall correlated best with mean hourly ascospore catches (correlation coefficient, r , ranged from 0.43 to 0.78) in both vineyards and in all years. First leaf and berry symptoms appeared between 7 and 24 May and between 25 May and 19 June, respectively, during the 6-year study. Disease started to progress slowly after the appearance of the first infected leaf followed by an exponential increase from early June. By the end of June, leaf and berry disease incidences ranged from 4.1 to 98.2 % and from 0.9 to 6.8 %, respectively, over the 6-year period. Leaf incidences showed significant relationship with corresponding cumulative numbers of trapped asco- spore in five out of 6 years, which was described by three-parameter Gompertz functions in each year. Results were compared and discussed with previous observations.

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