With infected stubble as source of primary inoculum, the development of net blotch on barley and its effect on grain yield were investigated over a two year period. Net blotch symptoms were observed from the first-leaf stage onwards. The severity of net blotch increased during the growing season. The penultimate leaf was entirely affected· within three weeks. From fungicide experiments, the yield loss caused by net blotch was estimated at 34 % of the disease-free yield. Net blotch decreased the grain yield through a decrease in kernel weight. In addition, net blotch infection of the floral bracts lowered the final grade of the grain.