Last week, the EPA determined that there is no benefit from neonicotinoid seed treatments on soybean. There complete ruling can be read here (http://www2.epa.gov/sites/production/files/2014-10/documents/benefits_of_neonicotinoid_seed_treatments_to_soybean_production_2.pdf ), and is based on an analysis of data published comparing treated and non-treated soybean. They conclude that “Published data indicate that in most cases there is no difference in soybean yield when soybean seed was treated with neonicotinoids versus not receiving any insect control treatment.” Furthermore, they find that the seed treatments only last during the first 3 - 4 weeks after planting, which does not overlap with activity of the more important soybean pests.
EPA’s decision is also consistent with what we see in Ohio. There are three main pests to monitor during the first 3-4 weeks after planting. One pest is slugs, which are not insects and are not affected by insecticidal seed treatments. Two is bean leaf leaf beetle, which can cause defoliation of emerging soybean. However, severe defoliation which decreases yield is rare (often the plant can grow out of it), and we have good foliar applications which are very effective in extreme cases. The third pest is seedcorn maggot. As the picture shows, this can be an important pest. However, seedcorn maggots are only a major concern when a green cover crop (like alfalfa) is tilled under and planting occurs 5 - 8 days later (Indeed, the picture was a special case from one of our trials where we purposefully timed it right for seedcorn maggot infestation. If we had waited 2 - 3 days more to plant, it is likely that we would not have seen any damage).
It is important to note that this is not an outright ban of insecticidal seed treatments on soybean. Rather, it should be a reminder of the need to carefully use these tools in an integrated pest management manner and to encourage safe, and profitable, soybean production. This is especially critical since the big driver for EPA's report could be due to the harmful effects of neonicotinoids on honey bees and other beneficial insects. However, soybean seed treatments have never really been under much suspicion for causing bee kills. There is far greater concern about the effects of corn seed treatments on bees, since there are several, well-documented cases of honey bees being killed during corn planting. Until an official ruling on neonicotinoid seed treatments on corn, growers are urged to use caution next spring during corn planting to avoid bee kills. We will be sure to add updates to this important issue over the winter.