Graduate Thesis Or Dissertation

Overwintering of Erysiphe necator and Inoculum Monitoring for Decision Aids

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  • Grape powdery mildew (Erysiphe necator) causes economic damages to grape worldwide due to the cost of management and injury to berries. Each region where European grapevine (Vitis vinifera) is grown experiences a unique epidemic, and disease prediction models that are based on empirical correlations of weather data to disease fail to predict disease accurately in regions with differing environmental conditions. Near real-time monitoring of grape powdery mildew epidemics using spore sampling and molecular detection techniques allowed grape growers to reduce fungicides applications by ~2.5 applications compared to their standard practice. Although spore sampling allowed growers to reduce fungicide applications, it is only a short-term solution to the lack of understanding of the factors surrounding initial inoculum availability. Additional factors affecting cleistothecia development and ascospore release conditions were also examined in order to improve current modeling efforts. This involved using controlled-environment studies to monitor cleistothecia initiation and development, and quantitative PCR was used to monitor ascospore release. Several established ascospore release models were tested for prediction accuracy, and an improved ascospore release prediction model was developed. The results of this work show that a portion of cleistothecia are capable of releasing ascospores before leaf drop and continue to mature and release ascospores throughout grape dormancy and into the following growing season. The results also show that an improved understanding of inoculum availability may allow grapevine growers to reduce management costs while improving disease control.
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