Increased pesticide use in Illinois is killing native oaks

While nearly the same amount of corn and soybean acres have been planted every year since the mid-1990s, the use of pesticides in Illinois has increased exponentially, according to USDA data.

Synthetic pesticide use has been a dominant agricultural practice since the 1950s, but use escalated dramatically in the mid-1990s when Monsanto, now Bayer, first released its Roundup Ready soybean and corn seeds, which allow farmers to spray directly on their crops, killing weeds without harming their harvest.

Before the commercial release of the genetically engineered seeds, glyphosate, the main ingredient in Roundup, accounted for a fraction of a percent of the total herbicides used on corn in Illinois. But by 2010, just over a decade after the commercial launch of glyphosate-tolerant corn seeds, glyphosate use accounted for more than 28% of all herbicides used.

That’s because after only five years of commercial use, dozens of weeds had evolved widespread resistance to glyphosate, becoming what some call superweeds. In response, farmers used more of the herbicide or switched to other products, such as 2,4-D and dicamba.

However, a 2024 study from the University of Illinois Urbana-Champaign indicates that the increase in pesticide use is causing significant damage to prairie grasses and trees across the state, particularly native oaks, hickory and box elders.

Researchers found a direct correlation between surrounding agriculture and damaged native vegetation. Field workers collected hundreds of leaf and soil samples at nearly 200 non-agricultural sites, like nature preserves, forests and wetlands, all within 10 kilometers of corn or soybean operations. They found at least one agricultural chemical at 97% of the locations, and observed visual signs of damage at every site. Chemicals from row crop fields, which can drift and harm unintended targets nearby, were the culprit.

Sample data from the sites date back five to 25 years, indicating that the increase in pesticide damage coincides with the massive increase in pesticide use.

The symptoms of pesticide damage in trees include cupped, curled, or twisted leaves, and they become more susceptible to stress from drought, infestations or disease. Repeated chemical exposure has even anecdotally led to tree deaths in some of the state’s oldest landmarks.

By 2023, about a pound of glyphosate was used on every acre of corn and soy planted in Illinois. Despite weed resistance and the rise in the use of other chemicals, it’s still the most widely used pesticide in the state.

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