ROOT ROT OF HEAD LETTUCE IN ONTARIO

Abstract

The symptoms of root rot of head lettuce in Ontario are similar to those described as occurring in New York and California. Unlike the disease from these two areas, however, the root rot in Ontario could not be correlated with ammonium toxicity. No fungus was consistently isolated and roots showing the early symptoms of the disease were frequently free from any organisms. The application of fungicides and/or nematicides to the soil prior to planting did not produce a significant difference in the disease incidence. Micro-organisms were considered to be secondary invaders in the disease syndrome. A field evaluation of lettuce varieties showed that leaf and cos varieties of lettuce were highly tolerant to the Ontario root rot.