Epidemiology of damping‐off disease (Pythium irregulare) in relation to density of Lepidium sativum seedlings

SUMMARY Controlled experiments on post‐emergence damping‐off, using small populations of garden cress seedlings ( Lepidium sativum ) inoculated with Pythium irregulare , demonstrate that planting density of the host population plays an important role in determining the rate of multiplication and the rate of advance of the disease. At high seedling densities the disease is transmitted readily between host plants, but at lower densities the greater distance between adjacent plants reduces the probability of successful transmissions, and this is reflected in the parameters of multiplication and advance. A simple negative relationship was found between the mean distance separating adjacent plants and both rate of advance of disease front and rate of multiplication of disease in a randomly inoculated seedling stand.