Weed response to ALS-inhibitor herbicide (sulfosulfuron + metsulfuron methyl) under increased temperature and carbon dioxide

Information on the impact of climate change on the growth of weed species and their sensitivity to herbicides could help to establish an efficient weed management strategy. Due to the excessive use of acetolactate synthase (ALS) inhibitor herbicides, resistance to those herbicides is increasing globally. It is thus crucial to find out whether the efficacy of these herbicides will change in the future due to the increase in carbon dioxide concentration and in the temperatures. This work therefore aims to evaluate the impact of temperature and carbon dioxide (CO₂) changes on the growth of Amaranthus retroflexus, Bromus tectorum, Chenopodium album and Echinochloa crus-galli, including the assessment of herbicide (sulfosulfuron 75% + metsulfuron methyl 5%) (SMM) efficiency in these weeds. A factorial experiment was performed in a completely randomized design with three factors, including two CO₂ concentrations (400 and 700 ppm), two temperature regimes (30/20 ℃ and 34/24 ℃ day/night), and six herbicide rates (0, 25, 37.5, 50, 62.5 and 75 g a.e. ha⁻¹) in four replications. As a result, it was seen that temperature and CO₂ concentration changes influenced the morphological parameters of the weeds. The main effect of the temperature regime on the herbicide's effectiveness, except for B. tectorum, was not statistically significant. The interaction of herbicide rates and temperature with the herbicide's efficacy was only significant for E. crus-galli; the highest efficacy was observed at 30/20 ℃ and at a rate 50% higher (75 g a.e. ha⁻¹) than the recommended one (50 g a.e. ha⁻¹). Increasing CO₂ concentrations enhanced the herbicide's efficiency and ALS enzyme activity inhibition in all the weed species, but had the greatest effect on C₃ weeds. Our results showed that temperature and CO₂ levels associated with climate change can interact to alter the efficacy of herbicidal weed control and that there are differences between plants with the C₃ and C₄ photosynthesis pathways. As a result, in the future, breeders and farmers could achieve the results desired by applying lower doses of this herbicide.