Field application of humic acid and thyme essential oil for controlling late blight disease of tomato plants under field conditions

Abstract

Effects of humic acid and thyme essential oil alone or in combination for controlling late blight diseased of tomato plants was tested under field conditions. The tested concentrations of humic acid had no inhibitory effect on Phytophthora infestans. While, thyme at concentrations 8.0 mL L-1 caused complete inhibition in linear growth of P. infestans. The highest inhibition in linear growth was obtained with thyme at 6.0 mL L-1 which reduced the linear growth by 92.2%. Moreover, under field conditions, results revealed that the most effective treatments are humic acid at 6.0 or 8.0 g L-1 combined with thyme at 6.0 or 8.0 mL L-1 which reduced the late blight incidence more than 81.3 and 78.4% during first and second growing seasons, respectively. Meanwhile, single treatments of thyme at 6.0 or 8.0 mL L-1 showed moderate effect. The highest increase in tomato yield was obtained with humic acid at 6.0 or 8.0 g L-1 combined with thyme at 6.0 or 8.0 mL L-1 which increased the tomato yield more than 53.3 and 46.9% during first and second growing seasons, respectively. Meanwhile, single treatments of humic acid at 6.0 or 8.0 mL L-1 showed moderate increase. The highest increase in β,1-3-glucanase activity was obtained with humic acid at 6.0 or 8.0 g L-1 when applied as single or combined with thyme at 6.0 or 8.0 g L-1 which increased the β,1-3-glucanase activity of tomato plants more than 137.0%.