Research Summary: Glyphosatiated: Species-specific impact of increased CO₂ concentrations on herbicide resistance

Waryszak, P., Lenz, T. I., Leishman, M. R., & Downey, P. O. (2018). Herbicide effectiveness in controlling invasive plants under elevated CO2: Sufficient evidence to Rethink weeds management. Journal of Environmental Management, 226, 400–407. https://doi.org/10.1016/j.jenvman.2018.08.050 

Written and edited by Justin Salva and Abigail Guinan

Summary: 

Increased atmospheric CO₂ is expected to cause physiological and morphological changes in invasive plants that past studies have suggested could lead to herbicide resistance (e.g., Ziska et al. 2004). However, past studies have been limited to a few agricultural weeds, making it unclear whether herbicide resistance will be a widespread phenomenon in invasive plants.  To test this quest more broadly, Waryszak et al. propagated 14 different invasive plant species found in southeast Australia, including grasses, herbs, shrubs, and vines in pots exposed to ambient and elevated concentrations of CO₂. The species were then split into groups and sprayed with 10 mL (recommended amount) or 20 mL (double recomended) of the herbicide glyphosate. Under elevated CO₂, invasive plant biomass tended to be higher, although biomass was only significantly higher for one species (the tropical grass Cenchrus clandestinum). Waryszak et al. did not see increased herbicide resistance under elevated CO₂. Out of the 14 plants, only one species (Anredera cordifolia) was significantly more resistant to glyphosate, whereas three species (Bromus catharticus, Verbena bonariensis, Senna pendula) were less resistant to glyphosate with elevated CO₂.  Thus, this study suggests that widespread glyphosate resistance is unlikely with elevated CO₂.
 

Take-home points:

• On the whole, most plants had the same response (or lack of response) to glyphosate under both ambient and elevated CO₂ concentrations.

• Vines and fast-growing species appear more likely to show an increase in glyphosate resistance when grown under elevated levels of CO₂

Management implications:

• Invasive plants are likely to have higher biomass with elevated CO₂.

• Double the recommended dose of glyphosate generally led to more dead plants (except for shrubs and vines, which were not affected by glyphosate at all).

• On average, elevated CO₂ did not change glyphosate effectiveness, although one of the species became more resistant and three became less resistant.

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