Chemical control of olive anthracnose and fungicide resistance profiles in Colletotrichum acutatum sensu stricto isolates from Greek olive groves

Olive anthracnose is the most destructive fungal disease of the olive fruit worldwide with the fungus Colletotrichum acutatum to be the main causal agent of the disease in Greece. A total of 12 commercial products, including antifungal compounds and inorganic salts, with various modes of action were evaluated by bioassays using detached olive drupes of two important olive Greek varieties, cv. Koroneiki and cv. Kalamon. Subsequently, in vitro fungicide sensitivity tests were carried out to investigate the resistance/sensitivity of 9 C. acutatum sensu stricto strains, originated from different Greek regions. The fungicides pyraclostrobin [Insignia (R)], difenoconazole [Score (R)], boscalid + pyraclostrobin [Signum (R)] and tebuconazole + trifloxystrobin [Flint Max (R)], were the most effective in reducing disease severity, or/and in inhibiting the conidia production by the fungus at high rates, in detached fruit assays. In vitro sensitivity tests revealed that all isolates were sensitive to difenoconazole, tebuconazole and pyraclostrobin, while most of the isolates were relatively resistant to copper oxide and copper hydroxide.