Use and side effects on the soil microbial activity of the essential oil from Thymbra spicata to control pepper blight Phytophthora capsici

The essential oil of Tymbra spicata showed good efficacy against Phytophthora capsici, the agent of pepper blight, both in the greenhouse and in the field. In greenhouse trials with naturally infested soil, the number of healthy plants of Capsicum annuum was increased from four to 10 per pot after treatment with different concentrations of the essential oil. The number of infected planes was reduced respectively from seven to two plants per pot. In a field trial, the number of healthy plants per m(2) was increased from 63 in the control plots to 111 in the treated plots. The soil Fumigant dazomet as a reference Fungicide was less effective both in the greenhouse and in the field. Investigations on the activity of the soil microflora showed that the essential oil had lower side-effects than dazomet. It reduced the population of soil fungi for up to 40%. while the dehydrogenase activity was reduced only for about 10%. Dazomet, however, reduced the population of soil fungi for up to 90% and the dehydrogenase activity for about 50%.