Water traps examined weekly were used to assess the activity of adult wheat bulb flies during the oviposition period in late July, August and eariy September. Traps were placed at various distances up to 1 mile (1-6 km) from known sources of infestation at Whittlesey, Cambridgeshire and at Rothamsted. Most flies were caught down wind from possible emergence sites and few were caught more than ^| mile (^0-4-0-8 km) away. The distribution of flies between traps was similar in both the first and second halves of the trapping period. At Whittlesey there was a significant positive correlation between the number of flies caught in a trap and the number of eggs laid in the field containing the trap. SUMMARYMethyl-bromide (1 lb/100 sq. ft), applied as in commercial practice, gave an increase in yield of both grafted and ungrafted tomato plants in glasshouse soils naturally-infested with root diseases. Grafted plants greatly outyielded ungrafted plants on treated and untreated soil where phytophthora stem and root rot was present. The efl"ect of the gas on corky root rot varied in the experiments and, on one nursery, control of the disease was not reflected by increased yield.