SOLARIZATION OF GREENHOUSE SOIL FOR PREVENTION OF PYTHIUM ROOT ROT IN ORGANICALLY GROWN CUCUMBER

Soil solarization in greenhouse tests was carried out in 1995-1997 by covering pre-irrigated soil with transparent plastic sheets to prevent root rot caused by the Pythium species in organically grown cucumber, where P. ultimum was the main cause of root rot.Densities of naturally occurring Pythium in the upper 10 cm soil layer were determined before, during and after solarization.Pythium was reduced considerably after four weeks in experiments 1 and 2 and after two weeks in experiment 3. Pythium was not recorded in solarized plots, but was still present in non-solarized plots.The mean of daily maximum soil temperatures measured 10 cm below soil surface was 38-43°C in solarized plots compared to 31-37°C in non-solarized plots during the first 14 days of the experimental period.Pythium root rot was negligible 13 weeks after solarization of the soil, whereas serious disease symptoms were seen on plants grown in non-solarized soil.This investigation showed that solarization in the summertime could reduce Pythium root rot, even in the temperate climate of Denmark.