Evaluation of three control strategies against grapevine powdery mildew in the central region of Chile

Abstract

The main strategy to control powdery mildew (Erysiphe necator [Schw.] Burr.) in Chilean vineyards is largely based on periodic fungicide spraying (up to 18 applications per season), which may lead to many environmental and human health risks. This study aimed to evaluate the effectiveness of three control strategies for powdery mildew: i) a Decision Support Strategy (DSS) with two to four fungicide sprays based on field observations of disease symptoms, ii) an Organic Management (OM) with six spray applications, using a novel fungicide based on Bacillus sp.  (Nacillus Pro®) and a biostimulant (Mamull®), and iii) a limited Traditional Strategy (TS) with only seven periodic sprays of synthetic fungicides. The experiment was carried out in the 2016-17 season in two furrow irrigated vine fields, trained in an overhead horizontal system, one with Cabernet sauvignon (CS) cultivar and another with Semillon (SE) cultivar, located in the Maule Valley. Untreated vines against powdery mildew were left in each experimental plot to assess disease pressure at the field level. The results showed that disease pressure was high in the Cabernet sauvignon field (disease severity in untreated vines was 42%), whereas it was very low in the Semillon field (disease severity was 1.1%). Thus, in the SE field, all evaluated strategies showed disease severity values similar or smaller than untreated vines. On the contrary, in the CS field, disease severity values were 0.6, 19.2 and 8.5 % for DSS, OM and TS strategies, respectively. Poor control of the OM strategy could be explained by low doses of Bacillus sp., which should be increased in future works.