Herbicides are the main means of controlling weeds. Recently, there has been increasing concern over the potential impacts of climate change, specifically, increasing temperatures and elevated carbon dioxide (CO2) concentrations, on the sensitivity of weeds to herbicides. A postdoctoral fellow in my lab, Maor Matzrafi, investigated the response of horseweed and lambsquarters to treatment with glyphosate under the higher temperatures and CO2 levels that are predicted to exist in northern California around 2050. Maor showed that the sensitivity of both weeds to glyphosate was reduced in response to increased temperature, elevated CO2 level, and the combination of both factors. He also found that glyphosate-treated plants lost apical dominance and initiated multiple lateral buds when grown under high temperature alone and the combination of both high temperature and elevated CO2 level. Maor's research shows that overreliance on glyphosate for weed control under the climatic conditions predicted for northern California in the future is likely to result in more weed control failures.
The picture below shows the translocation of glyphosate through a plant 48 hours after treatment (HAT), and the loss of apical dominance and initiation of lateral shoots one and two weeks after treatment (WAT) in lambsquarters.