Field evaluation of preseason applications of residential herbicides to control annual ryegrass (Lolium rigidum Gaud.)

Delaying crop sowing to use a non-selective herbicide to control the first germination flush of annual ryegrass results in reduced growing season length and hence yield potential.These studies aim to evaluate the efficacy of residual herbicides applied during the summer-autumn period to control annual ryegrassseedlingsemerging at the commencement of the growing season. Two herbicides, diuron and oryzalin, effectively persisted through the hot dry conditions experienced over the summer-autumn periods of 2000 and 2001 in the field at Merredin and Muresk, Western Australia. High rates of diuron (3.6 kg ha-1) and oryzalin (1.5 kg ha-1) applied to ryegrass pasture residue 157 days pre-sowing reduced annual ryegrass seedlings emerging at the start of the growing season by around 90%. A lower level of annual ryegrass control of between 75-80% was achieved for these same treatments applied to wheat stubble.Diuron at 2.5 kg ha-1 applied to annual ryegrass pasture residues 51 and 86 days pre-sowing resulted in a 93% reduction in ryegrass seedlings. Similarly, oryzalin at 2.0 kg ha-1 reduced annual ryegrass emergence by 99 and 95% for the 51 and 86 days pre-sowing application timings respectively. These results clearly indicate the potential for applying residual herbicides pre-season to control ryegrass emerging after the season commencing rains thereby allowing the earliest possible sowing time.