Efficacy of essential oils and biopesticides on Phytophthora infestans suppression in laboratory and growth chamber studies

Abstract

Control of late blight by alternative products is important for reduction of fungicide inputs and potato production costs. The efficacy of essential oils and biopesticides for inhibition of growth of Phytophthora infestans on media and suppression of late blight on potato plants in growth chambers was examined. Growth of pathogen isolates of diverse genotypes was evaluated on Rye B media amended with essential oils (lavender, thyme, thyme borneal, and oregano) and the biopesticide Serenade (Bacillus subtilis strain QST 713). Over 90% inhibition of pathogen growth was achieved with oregano and Serenade amendments. The protective foliar application of Serenade, an aerated compost tea (ACT), Effective Microorganism mix (EM), and oregano, resulted in disease suppression of 5–40% relative to the untreated control. ACT had no significant suppressive effects (0–15% reduction), EM resulted in mild suppression (15–30% reduction), and oregano and Serenade consistently resulted in moderate disease reduction (20–40%). No oil or biological treatment produced disease control comparable to the chemical control chlorothalonil, which resulted in disease reductions of 80–98%. Both oregano and Serenade resulted in some phytotoxicity at high doses. These results suggest that the natural products and biological amendments tested are not sufficient for effective late blight control by themselves; however, when used in combination with other established disease control practices, these approaches may contribute to improved, integrated, and more sustainable management options for late blight.