What farming practice is likely to increase the likelihood of herbicide resistance?

The choice regarding continual use of the same herbicides from the same chemical family is particularly relevant in the context of herbicide resistance. When a specific herbicide, or herbicides from the same chemical family, is used repeatedly on the same weed populations, there is a higher chance that some weeds will survive and reproduce.

This survival can occur because, within any population of weeds, there are often natural variations in genetic traits. Some individuals may possess resistance to the specific mode of action of the herbicide due to this genetic variability. When the same herbicide is applied consistently, those resistant individuals will have a survival advantage, leading to a gradual increase in the proportion of resistant plants in the population. Over time, this can render that herbicide ineffective, making it harder for farmers to manage weed populations and leading to increased costs and reliance on more toxic or harmful alternatives.

In contrast, practices such as limiting the number of herbicide applications, applying herbicides with little or no residual effect, or dealing with weeds that have only one generation per year do not contribute as significantly to the development of resistance. In fact, rotating herbicides with different modes of action is often recommended to mitigate the risk of herbicide resistance in weed management programs.