The new research concludes that a popular (and controversial) class of pesticides, neonicotinoids, has "negligible" benefits for farmers.
Neonicotinoids are the most widely used insecticides worldwide. They are typically deployed as preventive seed treatments in many grain and oilseed crops (including soybeans). But the scientific data on how useful this actually is, at least in the case of soy, is surprisingly thin.
Spyros Mourtzinis, a postdoctoral research fellow at the University of Wisconsin-Madison, was surprised to see how scarce information is on how useful these pesticides really are. The more he looked at the literature, the more he realized that the data doesn't seem to back this up.
Along with 22 other authors, he set out to analyze nearly 200 field studies on the effects of neonicotinoids on soybean yields. They found that half of the soy crops in the US use the pesticide as a preventive measure -- but without yielding substantial benefits, researchers found.
The results showed that, on average, treated crops produced 2 additional bushels per acre, compared to non-treated crops. A bushel sells for around $9, whereas the insecticide costs around $4 per acre. So you end up, on average, with an extra profit of around $15 per acre -- which, while more than zero, is not exactly remarkable. In fact, it's such a slim margin that the new study suggests that it's not a best management practice, and is oftentimes used unnecessarily -- it should only be used on fields that have a specific pest history, researchers argue.
"We've documented the costs and the downsides of neonicotinoids," said Christian Krupke, an entomology professor at Purdue University, who was one of the 23 researchers who authored a study on the topic.
"So the question we asked with this study was, what are the benefits? Do these insecticides pay off for growers? Do they prevent pest damage? And our findings are that the benefits are negligible."
Shawn P. Conley, a soybean specialist at the University of Wisconsin–Madison and also an author comments:
“I went into the project assuming this practice would have greater national effects; however, the data speaks for itself,” says Conley. “There are many agronomic factors such as early planting, narrow row spacing and seeding rate that farmers can implement that would play a greater role than neonicotinoids in maximizing economic yield.”
It's not just that the process isn't effective in most cases -- it has a damaging effect on a number of pollinators, and potentially the entire ecosystems. Numerous studies have shown the negative effect that neonicotinoids can have, and that's something farmers should account for in the future.
“Furthermore, the non-target impacts of the neonicotinoids used as seed treatments have been documented in dozens of studies by scientists all over the world. These impacts affect a wide range of organisms ranging from pollinators like honey bees to aquatic insects and the birds that depend on them for food,” concludes Krupke.
The study has been published in Scientific Reports.