Luciane Bertoletti Barros* and Neil McRoberts 
*University of California, Davis, One Shields Avenue, Davis, CA 95616 (lubbio@gmail.com)

Downy mildew, anthracnose and Isariopsis leaf spot are serious diseases in viticulture that can drastically reduce production during heavy infections. Weather affects pathogen development and can promote epidemics, with effects up to abcission of the affected organs. However, the effects of cultivar, rootstock, weather factors, other diseases, and defoliation are not well known. From 2011 to 2013 (two growing seasons), 10 leaves of one shoot per plant in six vines of each combination of cultivar and rootstock were monitored from budbreak until fall, for 540 leaves. Survival analysis was used to investigate the influence of factors on survival of leaves. The Kaplan-Meier estimator showed the proportion of grape leaves surviving to a specific time. The estimated median leaf survival time was 117 to 170 days (season 1) and 99 to 153 days (season 2). Survival analysis showed a significant increase in the risk of defoliation due to high relative humidity, rain, leaf wetness, and temperature. The effects of the monitored diseases posed highly significant increased risk of defoliation and their influence varied with cultivar and rootstock. Later cultivars had shorter leaf survival times than earlier cultivars, influenced by the inoculum level. Isariopsis leaf spot had less influence on leaf fall than the other two diseases.

Funding Support: CAPES