Efficacy of botanical extracts against late blight of potato under field conditions

Abstract:

Few people realise that a disease first recorded during the 1845 Irish famine still drains an estimated US$6.7 billion from global potato production every year—and synthetic fungicides remain the primary weapon. This research evaluated neem extract, garlic extract, and their combination against late blight (Phytophthora infestans) across three field seasons (April 2022-September 2024) at Porto Alegre, Rio Grande do Sul, Brazil. The neem-garlic combination held final disease severity at 53.6% compared with 91.2% in untreated controls, achieving a 41.2% reduction. Neem alone reduced severity by 30.5% and garlic alone by 20.7%. The chemical reference (mancozeb) gave 49.1% reduction. Tuber yield under the combined botanical treatment reached 26.1 t/ha, approaching the mancozeb check (27.6 t/ha) and exceeding the control by 69.5%. At roughly 38% lower input cost per hectare than the fungicide programme, the neem-garlic mixture offers smallholders and organic growers a viable eco-friendly alternative that delivers about 84% of the chemical’s protective effect.