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Of What Value Are Neonictinoid Seed Treatments In Soybean?
DR. SCOTT STEWART
JACKSON, TENN.
There has been a recent furor about the value of neonicotinoid insecticides such as Cruiser and Gaucho in soybean. This stems from a recent “benefits assessment” released by the EPA. This is the first step towards the banning of neonicotinoid seed treatments in soybean, mostly stemming from concerns about how these treatments affect pollinators. My response below in rather lengthy, but I wanted to get on the public record.
These seed treatments have been thoroughly tested in the Midsouth by my university colleagues and me. To be blunt, my greatest concern is not the potential loss of neonicotinoid seed treatments in soybean, but rather the potential precedent that is being set. What crop is next, what chemical, what about fungicides, what about new products under development? The reality of the situation is that substantial yield protection by the use of insecticide seed treatments (IST) in soybean is uncommon, even in the Midsouth. However there are a number of experiments where these yield increases have been observed. Although yield increases in the Midsouth from the use of neonicotinoid seed treatments typically only average 1-3 bushels, there are high risk scenarios where much larger increases would be expected. Also, there are examples where yield increases have been observed in normally low-risk environments. One of my colleagues just indicated that data from 72 replicated trials in Mississippi showed an average yield response of just over 2 bushels per acre. Not a huge number, but certainly enough to be a positive return on investment. The EPA report also suggests there may are suitable alternative foliar treatments. This is certainly not true for soil insects that feed below ground. It also shows a fundamental lack of understanding of real-world capabilities of pest management (weather limitation, logistical issues, scouting availability and capabilities, etc.), and not all injury can be undone once the pest is found).
I personally have documented statistically significant yield increase up 6-8 bushels per acre in my research trials in Tennessee. On several occasions, I’ve visited production fields where yield losses were clearly in excess of this when seed treatments would have prevented or mitigated this damage. The increased adoption (and push by NRCS) of cover crops further increases these risks from early season and soil insects, and thus, will increase the value of insecticide seed treatments in several crops.
Yes, unlike other crops such as cotton, corn or rice grown in the South, the value of at-planting insecticides in soybean is less consistent and more debatable. Although there are many potential pests, soybean plants have good tolerance to early season insect injury. However, what concerns me most is we are suggesting to ban the use of an insecticide primarily as a result of political pressure stemming from concerns over pollinator health. The EPA has assessed that insecticide seed treatments in soybean have little value, but the evidence that these same treatments are significantly affecting pollinator health is truly absent. Research in the Midsouth indicates that neonicotinoid seed treatments in soybean resulted in zero detectable levels in soybean flowers.* This same research did indicate that contaminated “dusts” emitted from planters could contaminate wild flowers surrounding recently planted fields. It has not been shown that these generally low levels are affecting the health of pollinators. Further, mitigation efforts (e.g., low drift seed lubricants, planter modifications) are being implemented or developed that should greatly reduce this potential source of exposure. In this geography, there is much more evidence suggesting a production value of neonicotinoid seed treatments than there is data indicating their involvement in “colony collapse disorder” of honey bees. Indeed, I don’t think there is evidence showing a general decline of honey bee health in the Midsouth.
We have a lawfully labeled insecticide seed treatment that underwent a thorough registration process and has been widely tested in the field. There are no proven effects on honey bees or other pollinators at truly field realistic doses stemming from their use on soybean seed. Alternative, foliar treatments are not necessarily effective and are not risk free. Neonicotinoid seed treatments in soybean should continue to be an option for growers to use as needed based on their local needs. Public opinion and political pressure from activist groups is not a scientific basis for cancelling a use for this important class of chemistry. It does concern me that ISTs in some crops (e.g., corn) are becoming a standard (base) treatment for seed companies, and thus, growers may use them even where their value negligible or where other options exist. We have not yet gone to this point in soybean, and I hope we do not. However, as long as these products are legal, I will recommend neonicotinoid seed treatments in soybean for at least some high risk scenarios (for example, when new or CRP fields are brought into production or where known pest problems indicate a high likelihood of yield protection). It is inappropriate to consider cancelling the use of an insecticide based primarily on the lack yield response shown in the much larger Soybean Belt of the Midwestern U.S. Averages can be very misleading, and after all, the use of these products is not mandatory. Perhaps the EPA should consider some regional limitations on neonicotinoid use in areas where benefits have not been shown (perhaps even a prescriptive approach). However, this seems like an issue that could be solved through communication with seed treatment providers and stakeholder education rather than legislation.
*Stewart, S.D., G. Lorenz, A. Catchot, J. Gore, D. Cook, J. Skinner, T. Mueller, D. R. Johnson, J. Zawislak, and J. Barber. 2014. Environ. Sci Tech. Potential exposure of pollinators to neonicotinoid insecticides from the use of insecticide seed treatments in the mid-southern U. S. Environ. Sci. & Tech. DOI: 10.1021/es501657w ∆
DR. SCOTT STEWART: IPM Extension Specialist, University of Tennessee
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