THE CONTROL OF DISEASES OF LETTUCE BY THE USE OF ANTAGONISTIC ORGANISMS II. THE CONTROL OF RHIZOCTONIA SOLANI KUHN.

Abstract

The antagonism of a number of bacteria, actinomycetes and fungi in pure culture on soil extract agar has been investigated. A considerable number of each of the three groups were highly antagonistic at 25° C., fewer were active at 15° C. and only a very limited number were effective at 5° C.In greenhouse experiments damping‐off of lettuce seedlings was substantially controlled by selected antagonists in sterile sand, soil or in sand/soil mixtures. Under similar conditions in unsterile soil, forms highly antagonistic in pure culture were generally ineffective in controlling disease. In one experiment control of disease in natural soil was obtained by the use of soil amendments, the effect being enhanced by the inoculation of one of these amendments with suspensions of antagonists.Attempts to control disease in the field by the use of soil amendments are described. In one year a substantial increase in the stand of healthy seedlings was obtained with certain treatments.