Effects of CO2 and temperature levels on glyphosate activity and growth of seven weed species

Changes in environmental conditions have a major impact on weed growth and their susceptibility to applied herbicides. We studied the effects of CO2 and temperature levels on the glyphosate (480 g/l Glyphosate Isopropylamin salt) activity and growth of seven weed species. Three temperature levels (control or normal temperature 26/16 °C (14/10 day/night), normal temperature + 3°C i.e., 29/19 °C and normal temperature + 6 °C i.e., 32/22 °C), and four CO2 levels (control i.e., 400 ppm, 600 ppm, 800 ppm, and 1000 ppm) were tested. Six doses of glyphosate were: i) ¼, ii) ½, iii) full dose (1440 g a.i./ha), iv) 2-times, v) 4-times, and vi) 8-times of the recommended dose, at 4-6 leaf stage. Generally, the increase in CO2 and temperature improved weed growth. For most weed species, the most favourable temperature and CO2 levels were 29 oC and 800 ppm to 1000 ppm. The ED50 (effective dose 50) value for Echinochloa colonum (L.) Link., Amaranthus retroflexus L., Amaranthus palmeri S. Watson, Portulacaa oleracea L., Solanum nigrum L., Sorghum halepense (L.) Pers. and Physalis angulata L. showed that some weeds will likely become tolerant to glyphosate with climate change. With increasing temperature and CO2 concentration, ED value increases, meaning higher herbicide doses are required to control these weeds. As a result, using more herbicides in agricultural areas in the coming years will cause producers to experience more costs and the herbicide resistance problem in weeds will increase to much higher levels.