Studies on the spread of leaf scald of barley from an infection focus showed that infected straw was the source of primary inoculum. The disease progressed mainly between adjacent plants but pockets of infection appeared in the crop at isolated positions several metres away from the source of inoculum. Sporulation occurred when free water was available and the conidia were trapped simultaneously with rainfall or irrigation. Some conidia were caught under windy but rainless conditions. Conidia were trapped at any time of day or night but few were obtained at any one time.