Downy mildew (Plasmopara viticola) is an important disease in grapes worldwide. Disease control is based on preventive management, including reduction of overwintering inoculum, green pruning, use of less susceptible cultivars, and fungicide application. The objective of this study was to describe the incidence, severity, and defoliation of P. viticola development in three cultivars, Concord, Bordô, and BRS Carmem grafted onto Paulsen 1103, IAC 766, and VR 043-43 rootstock on a commercial plantation in a subtropical area. To compare the response of each cultivar and rootstock combination, the experiments were carried out on ridges with a semi-trellis conduction system. Disease incidence and severity were assessed every 14 days from September to March 2011/2012 and 2012/2013 on the last 10 leaves on specific shoots of six plants of the nine different combinations. During the growing season, the weather conditions were favorable for development of the disease. Symptoms started in the vegetative phase with continuity during fruiting. There were differences among cultivars with BRS Carmem being most susceptible to mildew. Rootstock had no influence on downy mildew severity; however, the combinations showed the great influence of phenology on downy mildew. Defoliation influenced final production and phenology. Thus, the choice of less susceptible cultivars should be taken into consideration regarding phenology.

Funding Support: CAPES; CNPq