Grass Seed Production: Weeds, Herbicides and Fertilisers

Four weed species (Bromus mollis, Vulpia sp., Poa annua, Steltaria media) occur in 30% or more of all perennial ryegrass seed samples. Of the listed undesirable species, Avena fatua (wild oat) and Hordeum murinum occurred respectively in 5.3 and 3.5% of ryegrass seedlots. Only 6 herbicides are registered for use in grass seed crops in New Zealand, 2 for wild oat, and 4 for broadleaved weeds. The results of research on weed control in seedling and established seed crops (ryegrass, cocksfoot, tall fescue, phalaris, prairie grass) are presented. Fertilisers for grass seed crops discussed are nitrogen (N), phosphorus (P), potassium (K), lime and zinc. Autumn N is commonly used and will increase seed yields in early flowering species (Pestuca rubra, F. arundinacea), but in ryegrass variable results have occurred. Spring N should be applied at stem elongation. No responses to P have been reported for ryegrass, while in established cocksfoot responses to P and K have been reported. Overliming can induce Zn deficiencies, and of the grass species only prairie grass may require lime.