In most world crop-production areas, the evolution of herbicide-resistant weeds is becoming a major issue. This problem has become most severe across the Australian dryland crop-production region, where herbicide-resistant weed populations are threatening crop-production profitability and sustainability across 20 million ha. Widespread herbicide resistance has forced changes in agronomic and herbicide practices. This problem is particularly evident in Western Australia, where the frequency and distribution of herbicide-resistant weed populations appear to be greater than anywhere else in the world. Judicious use of herbicide mixtures and rotations can reduce the selection pressure for evolved resistance to any one specific herbicide. Additionally, agronomic practices, such as the double knockdown (preseeding sequential application of nonselective herbicides), increased seeding rates, and targeting of weed seed production to prevent seedbank inputs, are needed to reduce the selection pressure on allherbicides by reducing in-crop weed populations. However, these techniques are not without problems or limitations, and their weed control efficacy is inferior to that of most in-crop selective herbicides. The adoption by Australian farmers of the current limited technology is clear evidence of the value placed on the use of these alternate crop weed-control practices. The continued evolution of herbicide resistance more than justifies continuing research and development efforts to produce integrated strategies and smarter herbicide use so as to achieve sustainable weed management.
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