Weed management in Australian cotton. Our Past and Our Future

Abstract

Before the introduction of herbicide tolerant cotton varieties, weed management in Australian cotton systems was heavily reliant on combinations of residual herbicides before and at planting and in-crop. Options for post-emergent herbicides were limited, and in-crop weed control was via chipping and cultivation. Glyphosate tolerant cotton was introduced in 2000, and within a few years season-long tolerance was achieved. This resulted in extensive reductions in residual herbicides and chipping and a shift to heavy reliance on glyphosate. Subsequently, glyphosate resistance became prevalent in grass weeds, and later in broadleaf weeds. As a result, researchers and industry developed an industry wide herbicide resistance management strategy (HRMS). The HRMS focused on a relatively simple 2+2+0 approach (two non-glyphosate tactics in crop + two non-glyphosate tactics in fallow + allowing zero survivors to set seed). This approach facilitated the ability to re-introduce residual herbicides into the program. However, limited knowledge of the next generation of growers on how to introduce residual herbicides into the system, while minimizing the crop impacts resulted in a concerted effort by the industry to educate growers on how best to do this. Recently, cotton varieties were introduced with tolerance to glyphosate, dicamba and glufosinate. The industry now has widespread glyphosate resistance to a number of grass and broadleaf weeds. In addition, resistance to group 1, 4 and 22 herbicides is also common. This created a need for an updated HRMS aimed at minimising resistance across all herbicides. The backbone of the HRMS is to apply six different modes of action on grasses and broadleaves every two years and allow no survivors to set seed. This is a more complex approach than the 2+2+0, however extensive modelling has shown this to be an effective long-term approach. At least until further herbicide resistance challenges or herbicide tolerant technologies arrive.