THE RELATION OF ATMOSPHERIC TEMPERATURE AND HUMIDITY TO TOMATO LEAF MOULD (CLADOSPORIUM FULVUM)

Abstract

Summary A study of the relation of atmospheric temperature and humidity to tomato leaf mould (Cladosporium fulvum) has been made with a view to assisting growers to control the disease by cultural methods. The optimum temperature for the various stages of leaf mould is about 22° C. At 10° to 15° C. severe infection occurs under humid conditions, but the disease develops very slowly. Humidities exceeding 90 per cent, are very favourable. At 22° C. infection is severe at 80 per cent, humidity but is rare at 70 per cent. At 18° C. infection and subsequent development are considerably retarded at 80 per cent, humidity. Experiments indicate that seasonal variations in the severity of leaf mould are related to temperature. Data are given which show that humid conditions obtain in large glasshouses for several hours each night and that these conditions are largely responsible for the severity of leaf mould. Wetting of the foliage caused by overhead watering does not appear to favour the disease. Excessive watering produces turgid, susceptible plants. A basis for controlling leaf mould by cultural methods is suggested.