Effect of humidity on development of tomato powdery mildew (Oidium lycopersici) in the glasshouse

A series of experiments was carried out over four years in a glasshouse with computer control of humidity and temperature to investigate the effect of humidity on the development of tomato powdery mildew. Four relative humidities (RHs) (80%, 87%, 90% and 95%) at constant 19 degrees C were maintained over an eight-week experimental period during the Autumn. Disease was greatest at 80% RH and was progressively less with increasing RH to a minimum level at 95% RH on both inoculated plants, introduced to act as initial infection sources, and on adjacent uninoculated plants. The results indicate that high humidities may decrease severity of this disease in the glasshouse and may help management of this disease in the future.