Productivity of prairie grass (Bromus willdenowii Kunth) affected by sowing date and the head smut fungus (Ustilago bullata Berk.)

Effects of sowing date, fungicide seed treatments, and the head smut fungus Ustilago bullata Berk, on establishment, herbage, and seed production of prairie grass cv. Grasslands Matua (Bromus willdenowii Kunth) were measured in autumn‐ and spring‐sown field trials in New Zealand. Autumn seedling establishment from thiram‐treated seed relative to untreated seed was increased by 27% from the earliest sowing (early March), and by 65% from the latest sowing 8 weeks later. Infestation of seed with ustilospores of U. bullata reduced seedling establishment at all but the latest autumn sowing. Fungicide seed treatments had little effect on spring seedling establishment, but V. bullata infestation of seed reduced establishment compared with healthy seed, particularly after late sowings (early November). Herbage production was greater from early than from late sowings in both autumn and spring, and was less in plants grown from U. bullata infested seed than in plants from healthy seed. Enhanced autumn establishment from thiram‐treated seed led to improved herbage production when plants were young, but this effect disappeared about 18 weeks after late autumn sowing. Overall herbage production from spring sowing was more than twice that from autumn sowing. A 6‐week delay in autumn sowing led to a 58% reduction in seed production the following summer. Early autumn and spring sowings, together with adequate control of seedling diseases, are likely to give optimum herbage and seed production from prairie grass.