Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 16, 2006
Publication Date: October 24, 2006
Citation: Olanya, O.M., Larkin, R.P. 2006. Efficacy of Essential Oils and Biopesticides on Phytophthora Infestans Suppression in Laboratory and Growth Chamber Studies. Biocontrol Science and Technology; 16:901-917. Interpretive Summary: The potential use of biopesticides or natural products for late blight management can promote reduced inputs and improve sustainability of potato production. The objective of this research was to evaluate the effects of natural products and biopesticides on in-vitro inhibition of P. infestans in laboratory assays and determine the effectiveness of the natural products on development and suppression of late blight disease in growth chamber experiments. Growth of isolates of diverse genotypes was evaluated in petri-dish assays when Rye B media was amended with essential oils (Lavender, Thyme, Thyme Borneal, Oregano); and Serenade (Bacillus subtilis strain QST 713). Over 90% reduction of in-vitro growth was achieved with oregano and serenade amendments. With other essential oils, the inhibition of in-vitro growth was affected by product concentration and differed significantly among pathogen isolates. The protective foliar application of serenade, aerated compost tea (ACT), and Effective Microorganism mix (EM) resulted in disease suppression of 15-30%. Oregano and serenade consistently resulted in moderate suppression levels (20-40%). The disease suppression attained with chlorothalonil was highest among all treatments(80 to 98% reduction). These results suggest that natural products or biological agents by themselves are not sufficient for effective late blight control; however, when used in combination with other disease control practices, improved and sustainable management of late blight may be achieved.
Technical 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 Phytophthora infestans on media and suppression of late blight on potato plants was examined in growth chambers. Growth of pathogen isolates of diverse genotypes was evaluated on Rye B media amended with essential oils (Lavender, Thyme, Thyme Borneal, Oregano) and the biopesticide Serenade (Bacillus subtilis strain QST 713). Over 90% inhibition of growth was achieved with Oregano and Serenade amendments. The protective foliar application of biopesticides Serenade, an aerated compost tea (ACT), Effective Microorganism mix (EM), and oregano, resulted in variable disease suppression of 5-40% relative to the untreated control. ACT had no significant suppressive effects (0-15%), EM had mild suppression (15-30%), whereas oregano and serenade consistently had moderate reduction levels (20 to 40%). Chlorothalonil had significantly greater disease suppression (80 to 98% reduction) compared to biopesticides and essential oil. These results suggest that natural products and biological amendments by themselves are not sufficient for effective late blight control; however, when used in combination with other disease control practices, improved and sustainable management of late blight may be achieved.