Crops are more vulnerable to weeds now than before the advent of herbicides, according to a new study which says weeds pose an unprecedented threat to our food security.
The Broadbalk winter wheat trials are the world’s longest running experiment. They were established in 1843 to contrast different amounts and combinations of inorganic fertilisers compared with farmyard manure on wheat yields.
Since the mid-1960s, some plots have had herbicides applied and some haven’t. On plots where herbicides have never been used, yield losses to weeds have been consistently increasing since the 1960s.
The team looked at data from 1969 onwards – around the start of the so-called ‘Green Revolution’ when higher yielding wheat cultivars, and increased nitrogen fertiliser use became the norm worldwide.
The data demonstrates that increased global yields were only made possible with a concurrent increase in the use of pesticides.
Researchers from Rothamsted Research found that 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.
The team say this is due to weeds doing better than crops in a warming climate, coupled with a shift towards shorter crop varieties that get shaded out by the taller weeds.
And just like our crops, many weed species have also benefited over this period from increased use of nitrogen fertilisers.
In addition, more than half a century of consistent chemical spraying has also led to the rise of herbicide resistant weeds, threatening our ability to protect the gains in crop productivity achieved since the 1960s.
Lead author, Dr Jonathan Storkey, said: “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 study is published in the journal Global Change Biology.
Agricultural intensification and climate change have increased the threat from weeds
Jonathan Storkey Andrew Mead John Addy Andrew J. MacDonald
23 March 2021 https://doi.org/10.1111/gcb.15585