Most laboratory tests done to understand glyphosate resistance are done in sterile soil, void of those microbes. Schafer said Purdue's findings, published online early in the journal Weed Science, show that those microbes may play a significant role in how glyphosate affects plants.
"The soil you're growing the plants in is important to the results," Schafer said. "If we're growing in a sterile media, we could get some false positive results because the plants are more tolerant to glyphosate in those conditions."
Hallett and Schafer grew giant ragweed, horseweed and common lambsquarter in both sterile soil and field soil and subjected them to glyphosate. In each soil, strains of weeds both susceptible and resistant to glyphosate were tested.