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Why can herbicide-resistant crops lead to herbicide-resistant weeds?

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Rows of genetically modified barley plants grow in an outdoor test plot in Germany, with a yellow marker labeled 3 and protective netting overhead. — genetically modified organism Genetically modified crops are assessed for their impact on environmental factors such as soil quality.

Herbicide-resistant crops (HRCs) can lead to the development of herbicide-resistant weeds primarily through the process of repeated exposure and selection. Because HRCs are genetically engineered to survive specific herbicides, such as glyphosate, they encourage the liberal and frequent application of these chemicals to fields.123

This practice creates a strong selective pressure on weed populations. While the herbicide effectively kills susceptible plants, any individual weeds that possess natural genetic variations—such as mutations that allow for the overexpression of target enzymes, prevent herbicide interaction, or decrease herbicide uptake—are more likely to survive and reproduce. Over time, these resistant individuals become the dominant population in the field.32

Furthermore, the environmental impact is compounded by the potential for gene flow, where resistance genes from engineered crops can transfer to wild plant relatives via pollen and seeds. To mitigate the risk of selecting for these resistant weeds, it is essential for farmers to employ diverse weed-management strategies rather than relying solely on a single chemical application.324