Evidence for indirect effects of pesticide seed treatments on weed seed banks in maize and soybean

This study’s findings support the hypothesis that seeds coated with neonicotinoids and fungicides could undermine natural sources of biological weed control.

The study sought to answer whether pesticide seed treatments reduced the abundance of natural enemies (seed predators and pathogens), thus causing larger and less diverse weed seed banks. The results provided some support to this hypothesis. During the two years of study the mean density of germinable weed seeds were 40% and 32% greater in the site where coated seed was planted compared to the control (not statistically significant). Also, the weed seed banks were more diverse both years in the control site. Species richness and evenness of germinable seed bank did not differ between case and control plots. It was interesting to note that while there were no statistically significant difference between the case and control for either weed-seed richness or evenness, the diversity indices (which look at both evenness and richness) did show statistically significant differences. The researchers theorized this is due to subtle but consistent changes in all these parameters. Unfortunately, the researchers did not measure the natural enemy populations.