The dominant strategy followed by vine-growers in Chile to control powdery mildew (Erysiphe necator) involves schedule phytosanitary applications resulting between 9 to 18 fungicide sprays depending on the grape cultivar and the geographical area, mainly with sulphur applications. This large application of chemicals generates many environmental and human health risks To solve this, the present study aimed at evaluating the effectiveness of a Phytosanitary Decision Rule (PDR) proposed by French pathologists to rationalize fungicide applications against powdery mildew in grapevine. The PDR was evaluating in two irrigated vine fields, one of cultivar Cabernet sauvignon (CS, 1.56 ha) and another of Chardonnay (CH, 1.66 ha), in the Mediterranean climatic conditions of Talca Region, Chile. The experiment was carried out between 2009 and 2013. For the two experimental fields, two strategies to control powdery mildew were distributed in a randomized block design with four replicates: i) “Optimized traditional management” (OPT), which consisted in periodic applications (mainly sulphur), but with no more than nine treatments per season, ii) Application of a PDR based on field observations but with no more than four treatments per season. Untreated vines were left in each block to assess disease pressure at each studied season. Finally, a survey was conducted to know the practices of crop protection of traditional vine-growers (TVG) in the area, who carry out a “zero risk” strategy without limiting the number of phytosanitary applications. At veraison stage, clusters were observed to assess disease severity. The results show that powdery mildew control based on a PDR was as effective as schedule applications used by the OPT at experimental station for both vine fields. In the OPT and PDR treatments disease severity was lower than 5 %, which was considered as a threshold value for avoid in gloss of wine quality. For both cultivars disease severity was lower than that observed in untreated vines (close to 10% and 40 % for CS and CH, respectively). In the OPT treatment 7 to 9 applications per season independent of cultivar were made, whereas in the PDR treatment only 2-4 application were carried out. The differences are even greater when comparing the PDR with the TVG strategy in which, independent of the season and the cultivar, performed an average of 14 fungicide applications. Finally in the OPT and PDR treatments the cost per season was similar and fluctuated between US 322and415perhectareindependentofthecultivar.Thisvalueis60 322 et 415 par hectare, valeur qui est 60% inférieure au coût de la stratégie “risque zéro” de viticulteurs