The practical impact of sexual reproduction of grapevine powdery mildew on reduced fungicide sensitivity
PROJECT TITLE: The practical impact of sexual reproduction of grapevine powdery mildew on reduced fungicide sensitivity
Project leader: Minette Havenga (ARC Infruitec-Nietvoorbij)
Contact: havengam@arc.agric.za
Duration: 1 April 2023 – 31 March 2027
Problem identification and project objectives:
Powdery mildew cause serious economic damage in all grape-growing regions. Only a few sexual structures (chasmothecia) were observed in 1996-1999 in Stellenbosch. Since 2015, high numbers of chasmothecia are common on leaves at the later stages of the growing season in Western Cape vineyards. Asexual and sexual reproduction require different conditions, yet the primary inoculum for the infection is unknown. Therefore, disease models cannot effectively predict fungicide timing. Reduced sensitivity to QoI, SDHI and DMIs are suspected by industry experts. Two fungicide frac groups will be selected for this research depending on the industry needs. This will either be QoI and DMI or QoI and SDHI.
There is enormous pressure from the EU to reduce fungicide use. The biology and pathology of this fungus must be investigated to be able to understand what strategies can be implemented to improve the efficacy of management practices and subsequently reduce the number of fungicide applications. These include the role of post-harvest spray application on the reduction of inoculum source, timing of first application, the role of leaf litter, level of reduced fungicide sensitivity in different vineyards and whether registered fungicide concentrations can effectively control the pathogen. The project aims to determine the primary inoculum source, level of reduced sensitivity and the effect of sexual reproduction on reduced sensitivity. The aim of the project is not to determine whether specific products have a reduced efficacy but rather to evaluate biological factors that contribute to decreased management.