Herbicide-resistant weeds threaten crop productivity and food security. To avoid weeds evolving resistance, farmers often mix different herbicides, or apply them in cycle. But these strategies may be futile, suggests a study published online this week in Nature Ecology & Evolution.
Robert Freckleton and colleagues looked at the UK occurrence and herbicide-resistance of black-grass - a high-density weed which commonly competes with cereal crops. The authors also surveyed farmers about their use of herbicides - and how much their respective approaches cost. The team found that black-grass has been increasing in its spread and density across the UK since 1990, alongside a simultaneous growth in the amount and types of herbicide used. This suggests that black-grass is evolving resistance to successive herbicides. The increased weed densities lead to higher herbicide costs and lower crop yields, resulting in significant losses of profit.
The authors also found that increasing resistance is linked to the number of herbicide applications, and that combination or cyclical strategies did not prevent resistance developing. Current industry advice urgently needs to change to reflect this, the researchers conclude - and they recommend that farmers switch to weed-management strategies that rely less on herbicides, as it is inevitable that weeds will overcome even new agents.