The effect of quinone outside inhibitor fungicides on powdery mildew in a grape vineyard in Hungary

Abstract

Powdery mildew, caused by Erysiphe necator Schwein., is one of the most important diseases of grapes worldwide. In the present study, nine treatments consisting of chemical compounds and combinations of these compounds were tested against powdery mildew on Vitis vinifera cv. Merlot CI 181 and cv. Italian Riesling GK1. The aim of this study was to examine the effect of quinone outside inhibitor (QoI) fungicides, also called strobilurins, on powdery mildew and to see if resistant strains of the fungus were present. QoI inhibitors had never been used before in the vineyard or a nearby vineyard. Powdery mildew infection severity was monitored in the experimental vineyard in Cserszegtomaj, Hungary. At the same time, weather conditions and their effect on powdery mildew infection levels were monitored. No differences were found between the cultivars Merlot CI 181 and Italian Riesling GK1 in powdery mildew severity. However, there were differences in powdery mildew severity depending on the chemical compound and combination of compounds tested. The QoI fungicides provided little or no control of powdery mildew infection, and powdery mildew severity was not significantly different from that in the untreated vines. This suggests that the population of powdery mildew in this experimental vineyard was resistant to QoI fungicides. In the other treatments the level of powdery mildew infection was either significantly lower than in the untreated vines or there was no infection at all. These results show that the use of QoI fungicides selected for QoI resistance in the powdery mildew population. These results provide a warning that, QoI-resistant powdery mildew strains are likely to be a problem in Hungary in the future.