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Peanut scientists defend chlorpyrifos, seek alternatives for growers

Virginia Tech works to keep chlorpyrifos registered for southern corn rootworm in Virginia peanuts.

The registration of chlorpyrifos, the active ingredient in Lorsban, should continue. It is safe for pesticide applicators and consumers when label directions are followed. That’s the message Virginia Tech scientists are delivering.

Chlorpyrifos is the only chemical tool registered for Virginia peanut farmers against southern corn rootworm, a potentially devastating pest.

Speaking at the annual Virginia peanut growers production meeting Feb. 27 at the Paul D. Camp Community College in Franklin, Dr. Sally Taylor, Virginia Tech Extension entomologist, said NGOs, including the Pesticide Action Network North America, continue to petition the Ninth Circuit Court of Appeals to ban chlorpyrifos.

Several states, including Virginia, have introduced bills to prohibit the manufacture, distribution and sale of any pesticide containing chlorpyrifos.

Taylor noted that in 2015, the Ninth Circuit Court ordered the Environmental Protection Agency to revoke Lorban’s registration. The EPA decided not to fight this decision in 2016. But in 2017, the EPA determined the ban of Lorsban was unwarranted and allowed its registration until 2022 at which point its registration will be up for renewal again. 

In August 2018, the court ordered the EPA to revoke all tolerances and cancel registrations within 60 days. Taylor said this action would have taken it away from use in 2019 peanuts, but in September EPA appealed the decision asking for another trial. On Feb. 9, the Circuit Court decided to rehear the case.

“We haven’t heard when. It could be before season or after season. Let’s hope it’s after season since decisions on crop rotations have been made this year,” Taylor told the Virginia peanut farmer meeting. 

A potential challenge for Virginia farmers is a bill, HB 2850, introduced by Democratic Delegate Kaye Kory of Fairfax in northern Virginia, that would prohibit the manufacture, distribution, sale, offer for sale of any pesticide containing chlorpyrifos as an active ingredient. To date, it has yet to come up for a vote. Taylor said if the bill is passed into law, the ban would take place immediately.

“The bill authorizes the Virginia Department of Agriculture and Consumer Services to seize any such pesticides. Violation of the provision is a Class 1 misdemeanor and includes an additional fine of up to $500,000 if death or serious physical harm to any person is caused by the violation,” Taylor explained.

“Chlorpyrifos is a potentially dangerous material for pesticide applicators. But Virginia farmers are educated about pesticide safety and we follow label directions. Right now, Lorsban is the only tool we have,” Taylor stressed.

Taylor said the Virginia Peanut Growers Association and Virginia Tech are fighting for the continued use of Lorsban in Virginia because risk of exposure is very low when label directions are followed, and it is needed to protect one of Virginia’s most valuable and nutritious crops.

She noted that Virginia peanut farmers have done a great job of following Virginia Cooperative Extension’s research-based recommendations and only use Lorsban, or any other insecticide, when it is absolutely needed for pest control.  Currently, Lorsban is used on around half of Virginia peanut acres.

When it comes to using Lorsban for southern corn rootworm control in peanuts, Taylor said that light, sandy soils are at low risk for southern corn rootworm while heavy soils that retain moisture are at high risk. Irrigated land is always at high risk while late-planted fields are considered higher risk.

Virginia Tech and North Carolina scientists have confidence that the risk model developed by university researchers in the 1990s and 2000s justifies using the pesticide when it is needed for crop production.

Taylor said farmers should consider using Lorsban for southern corn rootworm in marginal fields if there is wet weather. She stressed that a marginal field means heavier soil not lighter, sandy soils.

Also, Lorsban takes time to work. “It takes one to two weeks to get it where it needs to go to protect your plants. If you’re applying Lorsban late, past mid-July, it’s probably not doing much good,” Taylor stressed.

Applying Lorsban too early, prior to June 20, is ineffective. Lorsban efficacy will diminish in heavy rains, so Taylor advises farmers not to apply the compound before there are pods to protect on the peanut plants.

“Applying any insecticide that you don’t need is a waste of money,” she stressed. “If you apply it and you don’t need it and we have an extremely dry year, you are at risk for spider mites. You are also at a higher risk for corn earworm because Lorsban is toxic to beneficial insects you have in the field.”

Virginia Tech is looking for alternative products to control southern corn rootworm in peanuts. She said Virginia Tech is seeking grower cooperators with high-risk fields to test products such as chlorantraniliprole, the active ingredient in Prevathon.

Prevathon is used to control caterpillar pests in cotton and soybeans. Taylor and her team want to see if it is effective to prevent southern corn rootworm feeding. Other products, such as indoxacarb, the active ingredient in Steward, have shown efficacy against closely-related pests. 

“We need to test all of our available options. North Carolina peanut researchers Drs. David Jordan and Rick Brandenburg have tried chlorantraniliprole, and other active ingredients, with mixed results. Unfortunately, until new products are tested and introduced, there are very limited alternatives to work with,” she said.

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Dr. Sally Taylor

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