Crop cultural and chemical methods to control grey mould on grapes

The efficiency of crop cultural (leaf removal) as well as of chemical methods (plant growth regulator, botryticide) to control grey mould caused by Botrytis cinerea was investigated in two seasons (2008 and 2009) on the varieties 'Pinot blanc' and 'Pinot gris' in the Moselle valley (Luxembourg). The application of the plant growth regulator Regalis® (a.i. prohexadione-Ca) led to a considerably more flexible cluster structure and a slight decrease of grey mould disease severity. The reduction of bunch rot infestation was of the same level than obtained by a single application of a botryticide (a.i. fenhexamid) before berries touching. Leaf removal reduced the cluster density slightly and proved to be more efficient against B. cinerea than the chemical treatments (reduction of grey mould disease severity of 57 % on average). Thus, leaf removal in the cluster-zone shortly after bloom can be recommended as an important tool in integrated as well as in organic bunch rot protection strategies. The best loosening effect on the cluster structure as well as the best B. cinerea reduction efficiency (75 % on average) was achieved when combining leaf removal and Regalis® application. The combination of leaf removal and botryticide application showed comparable results. Simulation of the B. cinerea epidemiology demonstrated that all treatments tested might allow for a longer maturation time due to lower infestation. The longest potential harvest delay until reaching an assumed threshold of 5 % disease severity was achieved by combining leaf removal and application of Regalis® or a botryticide (on average 11.6 or 9.9 days, respectively). The here presented strategies can thus be recommended to maximize wine quality in two ways – through a reduction of fungal contamination and/or an improvement of grape maturity.