Project number:
P04000325
Project title:
The practical impact of sexual reproduction of grapevine powdery mildew on reduced fungicide sensitivity
Project leader:
Havenga, M
Institution:
ARC Infruitec-Nietvoorbij, Stellenbosch
Start date:
2023
Project description:
This project will develop new knowledge regarding the primary inoculum, dominant reproductive strategy and basic biology of the powdery mildew fungus. Factors that will be evaluated include environmental requirements, the level of reduced sensitivity to DMI and QoI fungicides in South African vineyards and the effect of post-harvest application on chasmothecia development.
Powdery mildew causes 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 have been common on leaves at the later stages of the growing season in Western Cape vineyards. Sexual reproduction may lead to better-adapted individuals that are less responsive to fungicides. Due to climate change, Western Cape springs are becoming wetter. During bud break, conditions are now more favourable for the release of sexual spores.
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 and DMIs is suspected by industry experts.
The project aims to determine the primary inoculum source, the 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.
The results will provide information to calibrate prediction models accurately to the environmental requirements of the dominant reproductive system which will increase the efficacy of fungicide spray programs and reduce overall fungicide use.