Barley yield was evaluated at two planting dates, during three seasons, at the Carillanca Experimental Station (INIA, Temuco). Twelve cultivars and advanced lines of spring barley (two rows) were seeded, in the optimum date (September 1) and late (October 1,according to a common farmers' practice) in the spring season. Yield showed fluctuations between years and between planting dates. These differences could be explained by the date of foliar diseases appearance and its intensity levels. Climate, through hydrological balance, also palyed and important role in yield determination, but foliar diseases explained better the reduction in yield.