Weather conditions in Wallonia were exceptionally wet and cool in 2021 The weather conditions in Wallonia in 2018, 2019 and 2020 favored high yields, rising to more than 10,000 hl (45 hl.ha-1) in 2020. According to the Huglin index1 (HI), the 2018 growing season was temperate (1800 < HI < 2100) over most of Wallonia, while the 2019 and 2020 seasons were rather cool (1500 < HI < 1800) (Figure 1.b). These same three years saw a negative rainfall anomaly (ΔP = P - Pnormal) compared with the norm for the whole region, reaching a cumulative deficit of -300 mm between 1 April and 30 September. The 2021 growing season was very cool (HI ≤ 1500) everywhere in Wallonia and exceptionally wet, with a positive ΔP of up to +300 mm (Figure 1.c). As in vineyards in the south of France in 2018, long rainfall sequences allowed the spread of downy mildew. Between 1 April and 30 September 2021 (183 days), it rained on between 70 and 106 days (Figure 1.d), with an average of 3 to 6 consecutive days of precipitation for each rainfall event (Figure 1.e).