Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2003
Publication Date: 1/4/2004
Citation: Locke, J., Bowers, J. Effect of Formulated Plant Extracts and Oils in the Population Density of Phytophthora Nicotianae in Soil and Control of Pytophthora Blight in the Greenhouse. 2002. Journal of Plant Disease. v:88, pp. 11-16. Interpretive Summary: Phytophthora nicotianae is one of the most widespread and destructive soilborne plant pathogens. Many species of plants are susceptible to this pathogen and both susceptible hosts and the pathogen are found worldwide. Isolates of this ¿fungus-like organism¿ have been reported to cause root, stem, and crown rots, as well as fruit and foliar blights, on many agronomic and horticultural plants in seed beds, nurseries, fields, and landscape plantings. Symptoms of the disease usually develop rapidly during periods of high soil moisture associated with prolonged, rainy weather or frequent irrigation. Control measures frequently involve soil fumigation or soil drenches with fungicides to reduce soil inoculum. Due to environmental and safety concerns associated with fumigation and pesticides, the goal of this research was to evaluate the effect of formulated plant extracts and oils on soil populations of P. nicotianae and control of disease in the greenhouse. Treatment of soil with 10% aqueous emulsions of two formulations containing a pepper extract and mustard oil, two formulations of cassia tree extract, and a synthetic cinnamon oil formulation reduced the population density of P. nicotianae to or below the limit of detection in our assay (<0.04 cfu/cm3) 1 day after treatment of the soil. In the greenhouse, 10% aqueous emulsions of these formulations resulted in 93-97% healthy plant stand. The observed reduction in the pathogen population and increased healthy plant stand in the greenhouse indicates that these formulations of plant extracts and oils could have important roles in biologically-based management strategies for control of diseases caused by species of Phytophthora.
Technical Abstract: Formulated plant extracts and oils were investigated for control of diseases caused by Phytophthora. Soil infested with chlamydospores of Phytophthora nicotianae was treated with 1, 5, and 10% aqueous emulsions of formulations containing clove oil, neem oil, pepper extract and mustard oil, cassia extract, synthetic cinnamon oil, and the fungicide metalaxyl. Population densities of P. nicotianae were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P<0.05) differences among treatment mean values at each assay date. After 1 day, population densities were reduced to below the limit of detection (<0.04 cfu/cm3) in soils treated with 10% aqueous emulsions of two pepper extract/mustard oil formulations and two cassia extract formulations, and near the limit of detection for a synthetic cinnamon oil formulation. Populations increased and were detected in the assay over time, but after 21 days, populations of P. nicotianae in soil treated with one of the pepper extract/mustard oil formulations still was not detected. Formulations of clove oil, another pepper extract/mustard oil combination, the two cassia extracts, and the synthetic cinnamon oil reduced populations 98.4-99.9% after 21 days compared to the untreated control soil. The neem oil formulation and metalaxyl did not reduce pathogen populations at any rate tested. In the greenhouse after 35 days, 10% aqueous emulsions of a pepper extract/mustard oil formulation, a cassia extract, and the synthetic cinnamon oil formulation suppressed disease development in periwinkle (93.3, 93.0, and 96.7% healthy plant stand, respectively) compared to the untreated infested soil (0 plant stand). The observed reduction in the pathogen population and increased healthy plant stand in the greenhouse indicates that these formulations of plant extracts and oils could have important roles in biologically-based management strategies for control of diseases caused by P. nicotianae and other diseases caused by species of Phytophthora.