Effect of potassium silicate and electrical conductivity in reducing powdery mildew of hydroponically grown tomato

The effect of silicon on powdery mildew, caused by Oidium neolycopersici, was evaluated in five trials using two cultivars of tomato, ‘Ikram’ or ‘Cuore di bue’, grown in hydroponic systems. Silicon, as potassium silicate, was added at 100 mg L-1 of nutrient solution at three levels of electrical conductivity; 1.8–2 mS cm-1 (EC1), 3.9–4 mS cm-1 (EC2, 0.87 g L-1 NaCl) and 5–5.5 mS cm-1 (EC3, 1.74 g L-1 NaCl). Tomato plants were first inoculated with O. neolycopersici conidia 15–20 days after transplanting, with a maximum of five inoculations before final disease assessment. Drip or sub-irrigation methods, compared in two of the five trials, did not affect powdery mildew incidence and severity on leaves, 60 or 90 days after the first inoculation. The addition of NaCl to the nutrient solution generally reduced the incidence and severity of powdery mildew, with 0.87 or 1.74 g L-1 NaCl providing a similar effects. The addition to the nutrient solution of potassium silicate resulted in a signifi cant reduction of powdery mildew incidence and severity at the EC2 conductivity tested in all trials. The addition of potassium silicate to the control nutrient solution resulted in a similar or better level of powdery mildew management than the use of a nutrient solution with higher conductivity but no added with potassium silicate. The possibility and benefits of applying potassium silicate amendments in practice are discussed.&nbsp