Research Highlights

Research Highlights
Evaluating the Value of Neonicotinoid Seed Treatments for Soybeans

Photo: United Soybean Board

By Barb Baylor Anderson

Widespread preventative use of neonicotinoid seed treatments (NSTs) should be re-evaluated by producers and regulators alike, says Shawn Conley, University of Wisconsin soybean specialist. Conley, in work with researchers from other major soybean states across the Midwest, says the practice does not consistently yield economic or pest control results worthy of the investment.

“Our analysis, spanning 12 years and 14 key soybean-producing states, provides no empirical support for continuing the current approach of blanket NST use in soybeans,” says Conley, who is principal investigator of the research funded by the Wisconsin Soybean Marketing Board. “Our data suggest this approach provides inconsistent benefits, and that greater gains are likely from site-specific management practices rather than NST use.”

NST use has grown in popularity in recent years. Between 34-44 percent of U.S. planted soybean acreage is treated with NSTs, according to recent estimates, and may now exceed 50 percent. However, Conley notes no data have been collected by the U.S. Geological Survey since 2014. Insecticidal seed treatments in the neonicotinoid class include the active ingredients clothianidin, imidacloprid and thiamethoxam. Corn and soybean seed treatments represent the largest uses of neonicotinoids, he says, with soybeans having the highest active ingredient use per unit area.

For this work, Conley says soybean seed yield data from 194 studies were stratified in four growing environments based on soil pH and in-season weather conditions. Differences in average growing season temperatures and total precipitation were recorded among the four clusters. Across the entire region, the maximum average observed yield benefits due to fungicide plus neonicotinoid seed treatments reached two bushels per acre. Specific combinations of management practices minimally increased the effectiveness by 0.2 to 3.3 bushels per acre.

“The region where most U.S. soybeans are grown, the upper Midwest, benefits from a temperate climate and relatively few insect pests, particularly in the early season when NSTs would provide most crop protection,” says Conley. “Recent reviews of insect abundance in soybeans re-confirm this assessment – early season pests are still infrequently encountered across the area.”

Conley adds that another recent multi-state study of management tactics for soybean aphid, for example, found crop yield benefits and overall economic returns were not significantly improved by NSTs. An integrated pest management (IPM) approach combining scouting and foliar insecticide sprays when the established economic threshold was reached offered significant positive economic returns. Conley adds that highlights the decades-old approach of targeting pesticides to the presence of damaging levels of pest infestations remains the best strategy.

In addition, Conley notes prophylactic NST use can lead to negative effects on non-target organisms like bees. It also is difficult to predict early season pest populations.

“Although we do not have site-specific pest data to identify the mechanisms behind our lack of observed pest management benefits, our results are given context by historical data that reflect the scarcity of soybean pests targeted by this approach,” says Conley. “The period of pest protection provided by NSTs seldom aligns with economically significant pest populations. Absent economic benefits, there is no opportunity to provide benefit to most producers.”

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Published: Dec 7, 2020