Perennial ryegrass (Lolium perenne) grown for seed is planted in autumn for July harvest (first-year seed crop), then kept in production for subsequent yearly harvests. Plots of first-year perennial ryegrass planted in early November had only 3% as much stem rust in June as plots planted in mid-September. In other plots where fungicides were used to prevent rust development, seed yield from the November-planted plots was reduced by 23% compared with September-planted plots. In the second-year seed crop, stem rust severity in June was intermediate between severities in early- and late-planted first-year plots. The association of reduced stem rust severity with late planting for first-year crops was observed for five of six perennial ryegrass cultivars tested. Degree of reduction in disease severity due to planting date was greatest for the cultivars that had the highest disease severity in early-planted stands. Delay of autumn planting date may provide a useful cultural control method for first-year stands of perennial ryegrass seed crops.