A significant proportion of Australian wheat cultivars do not support leaf rust infections over winter and early spring periods despite available inoculum. To investigate why this occurs, tests of the leaf rust responses of 84 cultivars were conducted over 2 years in early (autumn) sown rust nurseries. More than 50% of the cultivars showed evidence of slow rusting and produced low to moderate area under disease progress curve (AUDPC) values. Many of the slow rusting cultivars showed features including leaf tip necrosis (LTN), long incubation period (IP) and longer latent period (LP), all characteristically associated with gene Lr34. The molecular marker csLV34, which is closely linked to Lr34, was applied to these wheats and confirmed the presence of Lr34 in all. Application of this marker identified Lr34 in a further 10 cultivars that could not be assessed for slow rusting because of the presence of seedling resistance genes effective against pathotypes used in field nurseries. It was concluded that a major role of Lr34 resides in reducing initial rust increase, thereby minimising inoculum development through winter and early spring, and subsequently delaying the onset of epidemics and lowering yield losses.