Blackrot - downy mildew control in small vineyards in southern Switzerland

Abstract: Blackrot caused by Guignardia bidwelli is causing damages in recuperated vineyardsin southern Switzerland planted with the cultivar Isabella. The source of inoculum is attributed toabandoned vineyards. Heavy and prolonged rains may also favor infection by Plasmoparaviticola on Isabella especially if a heavy load of primary inoculum can be expected. A 6 yearexperiment was made to test and confirm minimal necessary fungicide applications and timing tocontrol Blackrot and downy mildew. Infection conditions during the period between floweringand up to six week after, have led to heavy losses reaching 100% without adequate control. Acombination of the two pathogens was registered, with P. viticola bunch symptoms withoutvisible sporulation. We recommend therefore using fungicides or fungicide combinations with aneffect on both pathogens. Mostly two well timed sprays with an appropriate fungicide activeagainst both pathogens are sufficient to control fully the diseases on bunches and avoid loss.Under particular rainy situation a third applications gave 100% control. Timing should be beforerain events leading to prolonged leaf wetness during the time period between flowering and sixweek afterwards. Winegrowers in the area are not professional winegrowers or farmers, havinglittle specific knowledge, therefore they will apply fungicides only at particular date (Saturday)following the instruction of the manufactures. Applications are made by knapsack sprayers andvineyards are usually terraced irregularly often as pergola. Therefore we developed an easyapplicable scheme to determine application timing and an instruction system to determinefungicide concentration so to avoid over and under dosaging. Here we present the most relevantpoints we teach to our winegrowers.