Flower Debris Removal Delays Grape Bunch Rot Epidemic

Abstract

Field trials investigating the impact of removing flower debris (necrotic flower caps, filaments, anthers, aborted unfertilized ovaries, and aborted berries), which usually remain partly attached to grape clusters after bloom, on the epidemic of grape bunch rot caused by Botrytis cinerea were conducted in the white grapevine (Vitis vinifera L.) cv. Pinot gris (four experiments) and cv. Riesling (two experiments) in Luxembourg in the period of 2011 to 2014. Grape clusters remained untreated (control), or (i) flower debris was removed from the clusters (brush), or (ii) the clusters were treated with a botryticide (active ingredient fenhexamid; botryticide), or (iii) the clusters were brushed with a brush soaked in a botryticide suspension (botryticide-soaked brush) (all three treatments conducted at growth stage BBCH 73). On average of all six trials, bunch rot epidemics (day of the year reaching 5% disease severity) were significantly (p < 0.045) delayed compared to the untreated control by 3.7 (brush), 4.3 (botryticide), or 5.7 days (botryticide-soaked bruch), respectively. No significant differences in the delay of the epidemic were observed among the three treatments. Consequently, removal of flower debris might contribute to a reduction in or partial replacement of pesticide use in viticulture. Efficient technical solutions to automatically remove flower debris need to be developed.