Sensitivity of Colletotrichum acutatum to six fungicides and reduction in incidence and severity of chili anthracnose using pyraclostrobin

Anthracnose, caused by Colletotrichum acutatum, is one of the most destructive diseases of chili worldwide. Fungicides including picoxystrobin, azoxystrobin, difenoconazole, thiophanate-methyl and mancozeb have been used to manage anthracnose diseases for many years. Pyraclostrobin was introduced in China in 2016 to control chili anthracnose but has not seen widespread use. In this study, 40 isolates of C. acutatum were examined for their corresponding sensitivities to these fungicides using mycelial growth and spore germination assays. In greenhouse and field trials, the duration of protection of chili fruit from infection provided by pyraclostrobin against C. acutatum was determined. In vitro experiments showed that pyraclostrobin and azoxystrobin were inhibitory to both mycelial growth and spore germination, while mancozeb was only effective in inhibiting spore germination, and difenoconazole and thiophanate-methyl were effective in inhibiting mycelial growth. The results obtained suggest that these fungicides inhibited C. acutatum. It was observed that germ tube elongation and sporulation were reduced by pyraclostrobin. Pyraclostrobin provided protective activity for up to 96 h before inoculation, as well as curative activity up to 72 h after inoculation. In field trials, pyraclostrobin was effective in reducing the incidence and severity of anthracnose, and enhanced the marketable yield of chili. These results demonstrate that pyraclostrobin is a useful fungicide for the management of chili anthracnose.