A combination of factors means that crops are now more vulnerable to weeds than before the introduction of herbicides, according to a UK study. Researchers have exploited data from the world’s longest-running agricultural experiment, Rothamsted Research’s Broadbalk wheat trial, to highlight the threat posed by weeds.
The Rothamsted team have identified a number of factors driving increased yield losses to weeds. These include weeds performing better than crops in a warming climate, shorter crop varieties that are shaded out by taller weeds, weed species benefitting from the increased use of nitrogen fertiliser and increasing herbicide resistance among weeds.
The Rothamsted Research website reports that on the Broadbalk plots which have not been treated with herbicides, yield losses to weeds have been consistently increasing since the 1960s. Less than a third of the harvest was lost to weeds in the first ten years of the dataset, but between 2005-2014, this had risen to more than half, it says.
The study’s lead author, Jonathan Storkey, told the website: “Reducing yield losses from weeds is increasingly challenging because of the evolution of herbicide resistance and we can no longer rely on herbicides alone to counter the increasing threat from weeds.
“If we compare yield lost to weeds in the first ten years of the dataset weeds ‘robbed’ on average 32 percent of the yield compared to 54 percent in the last ten years of data.
“Our results demonstrate that weeds now represent a greater inherent threat to crop production than before the advent of herbicides and integrated, sustainable solutions to weed management are urgently needed to protect the high yield potential of modern crop varieties.”
The Broadbalk winter wheat trials (pictured top right) were launched in 1843 and the team examined data from 1969 onwards, around the time when the ‘Green Revolution’ took hold, with higher yielding wheat cultivars and increased nitrogen fertiliser use becoming the norm. They note that average temperatures over the main growing season for UK weeds have increased by around 2°C since 1969, giving weeds a competitive advantage over crops, which have less of a response to warmer temperatures.
Jonathan told the website: “Management and climate change have combined over the past 45 years to increase the threat from weeds. If we could no longer rely on herbicides, it could be argued that, in terms of weed pressure, the situation is now worse than before their widespread introduction in the 1960s.
“Our results highlight the need to diversify weed control strategies by complementing herbicides with non-chemical options including increasing crop competition and disrupting weed life cycles using fallows or more diverse cropping rotations.”
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