ROCKVILLE, Md. (DTN) -- Production of the insecticide Lorsban is ending, but its active ingredient, chlorpyrifos, is likely to remain on the agricultural landscape in the years to come.

Corteva Agriscience took the industry by surprise when it announced in early February that it was voluntarily ending production of chlorpyrifos in 2020. As the largest manufacturer of the insecticide, primarily under the brand name Lorsban, this loss will likely shrink chlorpyrifos availability in the short term, industry experts told DTN.

However, EPA has vowed to continue its re-registration of the active ingredient, ensuring that generic formulations of the chemical will remain legal to use in the years to come, the agency informed DTN. The EPA has recently defended the chemical against legal challenges based on concerns around the neurodevelopmental effects it can have on people, particularly infants. In recent years, some states and countries have initiated bans on chlorpyrifos, such as Hawaii, California, New York, the UK and the EU. See more here: https://www.dtnpf.com/….

EPA characterized Corteva's decision to drop chlorpyrifos production as a "strategic business decision" and said it will not affect the chemical's current registration review, which the agency has fast-tracked.

"EPA still expects to release the revised risk assessment for chlorpyrifos this fall using the best available science," an agency spokesperson wrote in an email. "Also, Corteva's decision will not affect other chemical manufacturers' ability to produce chlorpyrifos or farmers' ability to obtain the product."

The agency expects to release updated risk assessments and a proposed interim decision this year, with a final decision slated for 2022.

Corteva told DTN in an email that "We will continue to defend registrations of the product to allow existing product to be used by growers where registered."

"There are many other producers of chlorpyrifos around the world," the company added. Generic manufacturers of chlorpyrifos include companies such as FMC/Cheminova and Adama (formerly Makhteshim Agan).

However, sales of chlorpyrifos have declined steadily in the past two decades, Corteva noted. The U.S. Geological Survey shows that, in 2016, chlorpyrifos use had dropped below 5 million pounds annually, down from a peak of roughly 13 million pounds in 1994.

University entomologists agreed that it is no longer the first product growers reach for when fighting certain insect outbreaks.

As a broad-spectrum organophosphate insecticide, the chemical provides good control of many insect pests such as soybean aphids, noted University of Minnesota integrated pest management specialist Bruce Potter and Michigan State University entomologist Chris DiFonzo. It is also used to control a range of pests in cotton, alfalfa, citrus and tree nut production.

Use surged briefly during soybean aphid outbreaks in 2003 and 2005, DiFonzo recalled. "During the 2005 mega-outbreak, Lorsban supplies actually ran out in Michigan," she said in an emailed newsletter.

But, since then, other insecticides have emerged to replace the chemical in control of aphids and other insects, she added. "Less-risky alternatives became available," DiFonzo explained. "For the most part, [organophosphate] use in Michigan field crops has been replaced by Bt corn, neonicotinoid seed treatments and foliar pyrethroids."

However, Lorsban remained a valuable rotational chemical for many northern Midwest growers, especially those facing pyrethroid-resistant aphid populations in Minnesota, Potter said.

He said he expects Minnesota farmers to continue to rotate generic formulations of chlorpyrifos with these other tools in the future. "There is quite a bit of generic use already," he said.

DiFonzo cautioned that the loss of Lorsban on the market should alert the industry to the growing need to steward the chemicals that remain.

"The loss of Lorsban, disappearance of [organophosphates] in general, and insecticide resistance all highlight the need to manage insects like soybean aphid in an integrated way, exposing them to insecticides only as the last resort," she said.

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

(PS/AG)

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