An Ecological View to Herbicide Resistance Management.

Herbicide resistance is an emerging issue in several production systems in the United States. A major cause is the lack of management diversity and the repeated use of limited number of herbicides in the production system. Genetic diversity and selection pressure are two major driving forces of resistance evolution. Weed adaptation and weed species shifts in response to management tactics have been documented historically for tools/practices such as no-till, mowing, hand-weeding, among others. A similar fate has been expected for herbicides; the selection pressure imposed by herbicides are much greater than that of most other weed management tools used historically. A key issue is that growers simply shift to alternative herbicides upon the widespread evolution of resistance to a given herbicide without addressing the fundamental problem, leading to multiple herbicide resistance in weed populations. Effective and sustainable management of resistance requires an ecological view, with a systems approach to resistance management. In particular, placing emphasis on soil seedbank management that utilizes multiple tactics targeting all stages of weed growth is vital. The systems approach must consider resistance management in all crops included in the production system and also on all driver weeds within the system. For instance, current resistance management practices in the US are heavily focused on broadleaf weed species, with limited emphasis on grass weeds. As a result, herbicide resistance in grass weeds has started to emerge. A diversified management program that includes non-chemical tactics such as cover crops, moldboard ploughing and harvest-time weed seed control tactics along with sound use of herbicides will be essential for sustaining the utility of available herbicide options and securing the profitability of agricultural operations.