Seed and crop management company Syngenta Crop Protection LLC has petitioned U.S. EPA to increase the legal tolerance for a neonicotinoid pesticide residue in several crops -- in one case increasing the acceptable level by 400 times, according to a notice in today's Federal Register.

Syngenta, one of the biggest manufacturers of pesticides, wants to increase the allowable threshold for residues of thiamethoxam, a pesticide that has been linked to the decline of honeybees and other pollinators over the past several decades.

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.

Neonicotinoid pesticides are one of many factors that scientists say have caused a dramatic decline in pollinators, insects and animals that help crop production by carrying pollen from one plant to another. The United States has lost more than half its managed honeybee colonies in the last 10 years, according to the Pollinator Partnership, a nonprofit dedicated to the protection of pollinators and their ecosystems.

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 (Greenwire, Aug. 1).


Increases in neonicotinoids are especially concerning in forage crops like alfalfa, as bees collect pollen from the blooms, said Aimee Simpson, policy director and staff attorney for the advocacy group Beyond Pesticides.

"Instead of figuring ways to stop or reduce the use, it's significantly increasing the amount on forage materials and other crops," Simpson said.

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, where it can be toxic to bees. But foliar treatments are more likely to stick to the leaf, where risk to pollinators decreases.

"Growers depend on neonicotinoids and other crop protection products to increase crop productivity," said Bryan in an email. "Syngenta is committed to biodiversity, including thriving pollinators."

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.

"You always have to ask, what else is blooming out there at the time?" said Johnson. "If there's any flowering at all, you're going to have an impact."

EPA is accepting comments on the proposed changes, as well as amended tolerances for several other pesticides, until Oct. 6.