Winter fungicide sprays impact the dynamics of vineyard <i>Botrytis</i> populations
Botrytis populations in vineyards often show seasonal differences. Early season populations tend to be less pathogenic than those at harvest. This change probably reflects differences in competitive ability in winter versus summer conditions. Such a seasonal pattern was observed in a Waipara vineyard from 2008 to 2012. The population at owering was dominated by a Botrytis cinerea low pathogenicity haplotype; the population at harvest was dominated by a high pathogenicity haplotype. Since the 2013/2014 season, there has been a sudden change in this dynamic, with the high pathogenicity haplotype now dominant at both owering and harvest. This change in the seasonal dynamic was confirmed using microsatellite analysis. A possible explanation for the change in behaviour of the Botrytis populations was a change in management practice, with the addition over the past 2-3 seasons of a winter GelSeal spray for control of vascular pathogens. GelSeal is a trizole fungicide effective against Botrytis. The change to the vineyard spray programme may have disrupted the competitive advantage the low-pathogenicity population previously enjoyed over winter. The possible impact of this change on levels of disease will be discussed in relation to similar seasonal changes in European grape powdery mildew populations, where there is a strong relationship between early season populations and disease at harvest.