It's not clear that alfalfa growers fully knew that one of the most widely-used insecticides in their crop was about to be completely eliminated from use nationwide. But it was – nearly.

A complete withdraw of “tolerances” (legal uses) for chlorpyrifos (Lorsban, Lock-on) was scheduled for March 31, 2017, but on March 29, the EPA made a decision that it would not proceed forward at this time with a revocation of all uses for this pesticide.

Chlorpyrifos is one of the most widely used active ingredients in alfalfa in California, in other important California crops (e.g., almonds, citrus, cotton) and is used on over 200 crops nationwide and widely used overseas. California, with its high almond, alfalfa, citrus and specialty crop acreage, would have been especially affected.

In the opinion of many entomologists and pest control advisors, it is also an important tool in an integrated pest management program as a tool not only to control important pests but to prevent damage to beneficial insects and to prevent pest resistance to insecticides.

History

On Oct. 30, 2015, the EPA proposed to revoke all food tolerances for chlorpyrifos as a result of an earlier 9th U.S. Circuit Court of Appeals decision. This was in response to a lawsuit and allegations by Natural Resources Defense Council (NRDC) and Pesticide Action Network North America (PANNA) about human health and safety concerns. In November 2016, the EPA published its data and allowed members of the public to comment, which led to the decision in March 2017.

The decision by the EPA this week was widely watched by California farmers, and alfalfa producers in particular, many of whom breathed a sigh of relief since chlorpyrifos is very widely used. Chlorpyrifos (Lorsban, Lock-on) is a broad-spectrum insecticide effective on several major pests, particularly aphids and alfalfa weevils, and a significant component of an overall integrated pest management approach using diverse mode-of-action products.

This decision includes a promise to update its human health assessments (to be completed by October 2022), which will further guide the future of this pesticide. Human health concerns have caused some restrictions on chlorpyrifos used near residences and schools to be imposed in California separate from the EPA process (see labels for any guidance for pesticide use).

Usage in alfalfa

Although other states don't collect detailed pesticide use data, chlorpyrifos use in alfalfa is likely greater in California than other states due to its large acreage and long season (opportunity for pests). The use has ranged between 125,000 and 200,000 acres per year (out of 750,000 to 1.1 million total acres) over the past 10 years, with about 79 percent of applications made by air. Peak usage is February to April and July to August during periods when the prominent pests are seen: weevils and aphids in the spring, and aphids, alfalfa caterpillar and armyworms in the summer.  

–Excerpts from the University of California Agriculture and Natural Resources news release