Copper-alternative products to control anthracnose and Alternaria Brown spot on fruit of Tarocco sweet oranges and lemon in Italy

Abstract

Colletotrichum and Alternaria species, causal agents of pre- and postharvest anthracnose and Alternaria brown spot (ABS) on fruit respectively, have been recently reported as emerging fungal pathogens on citrus in the Mediterranean area, causing severe economic losses. The control of these pathogens is increasingly problematic, particularly in organic citrus orchards where disease management largely relies on the use of copper-based antimicrobials. With limitations in the use of Cu compounds imposed by the European Commission, due to the demonstrated noxious effects on environment, research for alternative formulations is encouraged. In this work, copper-alternative products (basic substances, plant extract, biocontrol agent and their combinations) were tested on sweet orange clones (‘Tarocco Scirè’ and ‘Tarocco Tapi’) and lemon clone (‘Femminello Siracusano 2 KR’) for two - three consecutive growing seasons in three citrus orchards within one of the most representative Italian citrus production areas to control natural infections on fruit caused by Colletotrichum and Alternaria species. Results showed that, even under different disease pressure levels, chitosan, Equisetum arvense and sweet orange essential oil-based products, alone and in mixture, significantly reduced disease incidence and severity compared with untreated controls, often showing comparable or better efficacy than copper. The copper-alternative products were also subjected to benefit-cost analysis, that showed an increase in the costs of phytosanitary treatments, differing according to the products, often covered by a positive increase in the marketable production compared to untreated control or copper-treated fruits. The good efficacy of copper-alternative products, alone and in mixture, indicates the potential of their sustainable and large-scale use, useful for replacing or reducing the use of copper in integrated and organic citriculture.