Global warming will create tougher weeds that require higher rates of herbicide to kill, according to a new study.
Published in the latest issue of Weed Science,the study shows that carbon dioxide acts as a fertilizer to grassy weeds, creating stronger plants that are more resistant to glyphosate, the world’s most popular herbicide.
Carbon dioxide levels have increased from a preindustrial era concentration of 280 parts per million to 379 ppm in 2005. Scientists expect those levels to further double by 2100.
Michelle Leishman, associate professor with the department of biological sciences at Australia’s Macquarie University, examined the effects of elevated carbon dioxide levels on four species of grass.
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The plants were grown in greenhouse experiments under today’s carbon dioxide levels of 380 to 420 ppm and elevated conditions of 675 to 715 ppm. They were then sprayed with glyphosate.
Leishman discovered a significantly higher survival rate for plants grown under the elevated carbon dioxide conditions.
“The increased tolerance to glyphosate that we found is most likely to be due to increased biomass growth of plants under elevated carbon dioxide conditions,” she said in an e-mail.
“A larger amount of foliage simply means that more herbicide is required.”
The three grass species that showed significantly higher survival rates under the elevated carbon dioxide conditions produced 39 to 83 percent more biomass and 24 to 67 percent more leaf area than the same plants grown under ambient conditions.
The only species that didn’t have a significantly higher survival rate experienced a five percent decrease in biomass and a 34 percent decline in leaf area.
The study concluded that the larger amount of biomass and leaf area was diluting the glyphosate in the weeds and rendering the herbicide less effective. The results are consistent with previous studies.
“This suggests that increasing atmospheric concentrations of car-b on dioxide might require an increase in application rates of glyphosate, which could have significant economic and environmental consequences,” said the paper.
In other words, global warming means farmers are going to be paying more for weed control and causing further harm to the environment by increasing the risk of water contamination.
“We hope that our research prompts herbicide producers to undertake more research into applications rates required under the many aspects of climate change,” said Leishman.
