Control of <i>Botrytis cinerea</i> and <i>Botrytis squamosa</i> in overwintered salad onions by fungicide sprays

Abstract

SUMMARY In 1974/75, 13 sprays of 0·2% a.i. thiram applied at 14 day intervals to overwintered salad onions reduced the incidence of Botrytis cinerea and significantly increased onion yields. In 1977/78 both B. cinerea and B. squamosa occurred, and 12 iprodione sprays at 0·1% a.i. applied at 14‐day intervals or 6 sprays at 0·2% a.i. applied at 28‐day intervals gave good control of B. cinerea and B. squamosa and significantly increased onion yields. Benomyl (0·1% a.i. at 14‐day intervals, or 0·2% a.i. at 28‐day intervals) failed to control either pathogen because of the development of carbendazim‐insensitive strains of the fungi. Effective control of both pathogens and increased yields were obtained with an application of 0·4% a.i. thiram in October and November followed by an application of 0·2% a.i. iprodione in December and January.