Syngenta has petitioned U.S. EPA to increase the legal tolerance for a neonicotinoid pesticide (thiamethoxam) residue in several crops. The petition would apply to alfalfa, barley, corn and wheat, both the crop itself and the straw and stover left over after cultivation. Syngenta is seeking to increase the levels from as low as 1.5 times for stover from sweet corn to as much as 400 times for hay from wheat.
Syngenta is seeking to change the tolerance levels because the company wants to use thiamethoxam as a leaf spray -- rather than just a seed treatment -- to treat late- to midseason insect pests, said Ann Bryan, a spokeswoman for the company.
Seed treatments are systemic, meaning the insecticide travels through the entire plant, including the pollen. But foliar treatments are more likely to stick to the leaf, where risk to pollinators decreases.
Scientists say neonicotinoids can suppress bees' immune systems, making them more vulnerable to viruses and bacteria. The Fish and Wildlife Service agreed to phase out neonicotinoids on wildlife refuges nationwide starting in January 2016.
The increased residues could become a problem if farmers are spraying thiamethoxam at a time when alfalfa is blooming, said Reed Johnson, a bee toxicologist and an associate professor of entomology at Ohio State University. But most commercial growers cut alfalfa before it makes flowers and pollen.
Switching from a systemic pesticide to a leaf spray can be a relatively good thing for bees, said Johnson, but if the spray drifts to other flowers nearby, pollinators could be exposed anyway.
EPA is accepting comments on the proposed changes, as well as amended tolerances for several other pesticides, until Oct. 6.