Diseases of grapevines Presently, the powdery mildew fungus (Erysiphe necator Schwein.) is controlled by the application of substantial amounts of fungicides. It is becoming increasingly clear that some of these chemicals can harm the environment, pose risk to human health, or become ineffective by the pathogen’s ability to develop fungicide resistance. Dependence on chemical disease control can be alleviated by the cultivation of grape varieties that are resistant to the pathogen. We are working toward this goal by studying the interaction between E. necator and Vitis vinifera in both a compatible and an incompatible interactions.