Growing our own poison–a vicious circle of more fungicides and more resistant Botrytis cinerea isolates

Grape production is seriously impacted by pests and diseases worldwide. Most producers rely heavily on the application of chemical pesticides to control pests and diseases of grapes and grapevines. With increasing rates of fungicide use, active ingredients may decrease in efficacy or become inefficacious due to the emergence of resistance in the organism targeted by the treatment. This research was conducted with the aim of assessing the sensitivity of Botrytis cinerea to five fungicide formulations (active ingredients: boscalid, cyprodinil + fludioxonil, fenpyrazamine, fenhexamid, and pyrimethanil), four of which have been registered and used for more than 10 years in Croatia. Even at the highest concentrations tested, pyrimethanil, boscalid and fenhexamid caused fungal inhibition at a rate significantly lower than 90%. Conversely, cyprodinil + fludioxonil had inhibition rates greater than 90% for 72% of the isolates. Finally, the fungicide fenpyrazamine, which is not registered for use in Croatian viticulture, resulted in fungal inhibition rates of less than 40%. To our knowledge, this is one of the few studies conducted in the Slavonia region of Croatia on the potential emergence of resistance to chemically active ingredients in B. cinerea populations. The results of the present study show that B. cinerea resistance to several active ingredients is of significant concern due to the small number of registered products available in Croatia to combat the disease this fungus causes on grapes.