Effect of organic soil amendments on damping-off of lettuce caused by Corticium praticola

Ten organic amendments were added to unsterile soil which was contaminated 14 days later with Corticium praticola and sown with lettuce seeds. Substantial increases in final stands of seedlings were obtained with grass meal, bran and wood cellulose. Corn and barley meal, linseed cake and fish meal decreased final stands; molassine meal, potato starch and peptone had relatively little effect. Seedlings grown with wood cellulose were very chlorotic and stunted. Up to 30% of lettuce seeds sown in soil which, 180 days earlier, had been amended with corn meal and contaminated with C. praticola became colonized by the fungus. None was colonized in unamended soil or in soil amended with grass meal. Ninety days after amendment and contamination fewer seeds were colonized in soil amended with grass meal than in unamended soil. The amendment of soil with grass meal was as effective as thiram seed treatment in protecting lettuce seedlings against C. praticola and grass meal was particularly effective in reducing both the numbers of seedlings attacked and the survival of the fungus in the soil.