Efficacy of cultural control methods for combating herbicide‐resistant Lolium rigidum

Herbicide-resistant populations of annual ryegrass (Lolium rigidum) are estimated to affect crop production on about 5000 farms in southern Australia. In order to manage resistant populations, some farmers have adopted a two-to-three-year pasture phase which allows use of grazing by sheep, and non-selective herbicides to deplete the weed seed-bank. However, in low-to-medium rainfall zones, where financial returns from pastures are relatively low, farmers have generally combined cultural practices for weed management with the use of alternative herbicides, mainly trifluralin. Used singly, none of the currently available cultural techniques provides an adequate level of weed control. However, when used in carefully planned combinations, extremely effective ryegrass control can be achieved. Some of the important cultural practices for ryegrass control include delayed sowing (sometimes in conjunction with a shallow autumn cultivation); stubble burning; cutting the crop for hay or green manure, increased crop density and capture of weed seeds at harvest. Selection of crop species and cultivars with superior weed suppression potential is also receiving considerable attention.