Resistance genes constitute a fragile heritage.
Their effectiveness, and thus their usefulness, is subject to the risk of evolution in pathogen populations.
Powdery mildew and downy mildew of grapevines have a high evolutionary potential because they combine several characteristics that promote their adaptation (production of large quantities of spores, good dispersal abilities, large population size in Europe due to favorable climatic conditions and the near-exclusive use of susceptible grape varieties).
Several documented cases of resistance gene erosion have been reported for downy mildew and powdery mildew in Europe.
To minimize these risks of resistance breakdown, the vineyard should not be subjected to excessive inoculum pressure.
This requires managing the plots according to good agronomic practices, with appropriate prophylaxis against fungal diseases.
Additionally, at least two preventive fungicide treatments are required, generally around flowering stages, to control any virulent strains that may have emerged. These treatments must be adapted to the disease pressure of the vintage, following the recommendations of technical advisors. Additional treatments should be applied if conditions demand.