SUMMARY: Examination of the trap catches of barley mildew spores at Hatching Green (1971), Wellesbourne (1970 and 1971) and Paddington (1961–1970), and analysis with respect to meteorological data, indicate an increase of catch with wind strength in the vicinity of the sources; at greater distances strong winds will decrease the catch. Spore catches increase rapidly with day maximum temperatures above about 19°C (66°F) but reach a maximum in the vicinity of 24°C (75°F). The effect of an adjacent winter barley crop is discussed.