Scientist Sees Weeds as Indicators of Climate Change

Japanese stiltgrass, Microstegium vimineum. Source: Chuck Bargeron, University of Georgia, Bugwood.org

There’s an age-old saying about how kudzu ate the South. Lew Ziska, a scientist with the USDA Agricultural Research Service in Beltsville, Maryland, has taken the adage to heart.

For the past 25 years, Ziska has been studying the effects of carbon dioxide on crop plants. In the mid-1990s, something changed. Global carbon dioxide concentration levels went above 387 parts per million (ppm) and the Kyoto Protocol, an international treaty pledging to reduce greenhouse gas emissions, was signed. Ziska says there was no coincidence, but an entirely different interest: human health. Instead of crops, Ziska began looking at weeds, and in particular, ragweed.

Ragweed, a perennial, produces copious amounts of seed. People allergic to ragweed suffer weeks of coughing, sneezing, and plain misery.

“The climate is warming,” Ziska said. “A warming climate facilitates widespread distribution of ragweed. You’ve got a recipe for a perfect storm.”

Ziska and his team have been conducting research to address basic questions about climate and weed population dynamics. For example, herbicide efficacy could be hindered by extreme rainfall that washes away chemicals. High winds increase drift and complicate spraying practices. In addition, elevated carbon dioxide levels could change how herbicides work, even making them less effective. For example, he found that Canada thistle regrows after glyphosate applications in high-carbon-dioxide conditions. The silver lining is that there are tools other than chemicals in the IPM tool box.

Ziska and his team warn that the evolutionary potential of invasive species should be given more attention at the molecular level, as such changes could lead to rapid range expansion.

“There are an increasing number of studies suggesting that many invasive plants are capable of rapid genetic change and evolutionary adaptation, which may speed their spread,” says Ziska.

This is not good news for those with allergies or who want to bring Japanese stiltgrass under control in their back pasture or favorite national park.