Powdery mildew disease of cereals caused by Erysiphe graminis is an important disease wherever cereals are grown. Reduction in yields of up to 30 per cent has been recorded overseas but similar estimates have not been published in New Zealand. Attempts to control E. graminis by breeding resistant varieties have met with limited success. Chemical control appears to be the most promising method of combating the pathogen and with the introduction of systemic fungicides, economic control of many fungal pathogens, including E. graminis, is now possible. Triarimol, one of the new systemic fungicides is currently under trial in several countries. The ability of triarimol to control E. graminis under New Zealand conditions was investigated.