Essential oils and their combinations with iprodione fungicide as potential antifungal agents against withe rot (Sclerotium cepivorum Berk) in garlic (Allium sativum L.) crops

• Antifungal power of non-phytotoxic essential oils is useful to control white rot.
• Essential oils present positive interaction with synthetic fungicides.
• Essential oils can be used to reduce doses of chemical pesticides in garlic crops.
• Laurus nobilis and Tagetes filifolia essential oils can be used into integrated pest management.

This study was conducted to evaluate essential oils (EOs) and their binary combinations with fungicide iprodione (Ip) as a potential fungicide against Sclerotium cepivorum Berk in order to reduce the amount of pesticide applied in garlic crops. Five essential oils (EOs) from different plants grown in Argentina were studied: Tagetes minuta L. (Su), Tagetes filifolia L. (An), Origanum vulgare L. spp. Vulgare (OCom), Origanum x majoricum (OMen), and Laurus nobilis L. (Ba). The chemical composition of EOs was analyzed by GC–MS. The minimum fungicide concentration (MFC) and minimum inhibitory concentration (MIC) were determined for each compound. A total of 84 combinations of EOs and Ip were assessed looking for synergistic interactions. A phytotoxicity assay was carried out to identify EOs with a potential negative effect on garlic. The effect of EOs, Ip and mixtures on white rot was evaluated in a field study. Fungicide Ip had the best antifungal activity in the in vitro test. OMen and OCom showed high antifungal activity, but also had a strong phytotoxic effect on garlic plants. Su had a moderate antifungal effect with distinguished synergism with Ip, but none can be used due to its phytotoxic effect. An and Ba both had moderate antifungal activity. These EOs had no negative effect on garlic germination and production, being non-phytotoxic for this crop. In this study, the combinations of An and Ba them with Ip have synergistic interactions. Sclerotia density and disease incidence were reduced by these mixtures in a field study. In conclusion, An and Su could be used as natural fungicides to control white rot in garlic, reducing the fungicide dose required. However, future studies are needed to adjust final concentrations to be applied in field crops.