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Losing Lorsban: Looking Ahead to 2022

Authors: Marissa Schuh (UMN), Robert Koch (UMN), Theresa Cira (MDA), Raj Mann (MDA), Bruce Potter (UMN), and Anthony Hanson (UMN). Reviewed by Bill Hutchinson, UMN. 

What’s going on with chlorpyrifos?

In a pre-publication of a final rule released on August 18, 2021, the EPA announced  that the agency is revoking all tolerances for chlorpyrifos. A “tolerance” represents the maximum level of pesticide residue legally allowed in or on raw agricultural commodities and processed foods. Revoking of tolerances will stop the use of chlorpyrifos on all food and feed, taking effect six months after the final rule is published. See 40 CFR Part 180 for a list of chlorpyrifos tolerances on food commodities. The pre-publication announcement from EPA indicates that growers can still use chlorpyrifos through the end of the 2021 growing season.  Non-agricultural uses are unaffected by the final tolerance rule. 

A Quick Review of the Chlorpyrifos Saga

In 2007, the Natural Resources Defense Council (NRDC) and Pesticide Action Network North America (PANNA) submitted a petition to the Environmental Protection Agency (EPA) to revoke all tolerances and cancel all registrations for chlorpyrifos based on adverse human health effects. The EPA made a final decision, denying this petition in 2019. However, in a ruling issued on April 29, 2021, the Ninth Circuit Court of Appeals vacated the 2019 denial of the petition and instructed the EPA to either modify chlorpyrifos’s tolerances and publish findings to show they are safe, including for infants and children, or to revoke all chlorpyrifos tolerances within 60 days. The EPA announced on August 18, 2021 that “Based on the currently available data and taking into consideration the currently registered uses for chlorpyrifos, EPA is unable to conclude that the risk from aggregate exposure from the use of chlorpyrifos meets the safety standard of the Federal Food, Drug, and Cosmetic Act (FFDCA). Accordingly, EPA is revoking all tolerances for chlorpyrifos.” The revocation of all tolerances will take effect six months after the publication of the final rule. Therefore, growers can still use chlorpyrifos through this 2021 growing season.

What products are affected by this decision, and why was it made?

Chlorpyrifos is an active ingredient in many commonly used insecticides such as Chlorpyrifos, Govern, Hatchet, Lorsban, Lorsban Advanced, Vulcan, Warhawk, Whirlwind and Yuma, and formulated mixtures such as Bolton, Cobalt Advanced, Match-Up, and Stallion. It is a neurotoxic chemical capable of affecting a wide range of animals including many arthropod pests, but also humans and non-target organisms. Chlorpyrifos interferes with the normal functioning of their nervous systems by binding to acetylcholinesterase (AChE), preventing the breakdown of acetylcholine. Subsequent accumulation of acetylcholine causes over stimulation of nerves which can result in paralysis and death. Chlorpyrifos is also a source of contamination in multiple surface water bodies in Minnesota and can pose a substantial risk to human health and the environment.

Chlorpyrifos and Vegetables 

Chlorpyrifos, most commonly used in vegetables in the product Lorsban, has been registered for a variety of pests across vegetable crops.  These products can be used for the next six months, so through the rest of this growing season, but come the 2022 growing season, new tactics for managing some pests will be needed.

Vegetables have Many Products Registered for Caterpillars, Aphids, and Other Pests

The interactive allows you to quickly see what products are effective against which pests. Screengrab: Marissa Schuh, UMN Extension.

The go-to spray guide for Minnesota vegetable growers, the Midwest Vegetable Production Guide, is available as a huge PDF, a hard copy, and an interactive database.  The guide lays-out effective products for pests across all vegetable crops.  For most insects, it lays out lots of non-Lorsban options for pests.

Ladybeetle larvae are often not noticed, but are voracious eaters. Photo: Entomart via Wikimedia Commons.

If you have found yourself reaching for Lorsban in the past for small, soft bodied insects like aphids, losing chlorpyrifos means it is a good time to look over your spray records.  Insects like aphids are often controlled by natural enemies, and consistent aphid issues may indicate a need to use more natural enemy-friendly chemistries early in the season to preserve these natural enemies.  They do not reproduce as quickly as many of the pests we are trying to control, so taking the good bugs out early in the season means there is a large window where you are getting no help from beneficial insects.

A Problem Area: Cabbage Maggot

Growers of cole crops are in a tougher spot in a post-Lorsban world.  The biology of cabbage maggots made this pest hard to manage with chlorpyrifos, and options will be more limited going forward.  Adult flies emerge early in the season (often around the same time the weed yellow rocket blooms).  Adults look similar to houseflies, and they lay eggs on or near the the base of recently emerged or transplanted cole crops.  Once eggs hatch, maggots burrow directly into the plant, where they are protected from pesticide sprays.

Cabbage maggot in cauliflower. Photo: Marissa Schuh, UMN Extension.

Time to Brush up On Cultural Controls

For Everyone

  • Cabbage maggot has multiple generations a year, and while the later ones don’t damage crops, they do determine the size of next year’s cabbage maggot population.  Destroy this year's brassica residue promptly.

  • Avoid brassica cover crops

  • Make sure to terminate cover crops and till weeds well before planting to reduce how attractive the area is for egg-laying flies.

  • If cabbage maggot pressure is consistently high, use degree days to plant cole crops once the peak flight of cabbage maggot has passed

For Smaller Acres

  • One option that is viable for small plantings is exclusion netting.  Trials of large-scale netting in Michigan turnips has shown that the netting can exclude cabbage maggot while producing larger turnips faster, likely due to the microclimate the netting provides.  

  • For growers on smaller acres, rotating so that brassicas don't follow brassicas, especially in double cropped areas, will help keep populations down.  Flies can travel ~1 mile in search of egg-laying sites, but any bit helps.

For Larger Acres

  • For growers with access to more acres and rented land, rotation will become more important. The greater the distance between last year’s brassicas and next year's brassicas, the better.  Adult flies are thought to be able to fly approximately 1 mile.

Chemical Options for Cabbage Maggot and Root Cole Crops

For direct-sown turnips and radishes, some pyrethroid products like Mustang Maxx can be sprayed on the top of plants.  Research in Michigan has shown that well-timed, very directed sprays can reduce cabbage maggot damage in turnips.  The University of Minnesota’s Cabbage Maggot weather model is a key tool in timing applications, as the egg-laying flies will need to contact the product to be effective.  This means that timing sprays for peak cabbage maggot flight will be needed.

Percentage of damaged (white) and undamaged (grey) turnips in a 2019 trial. Photo: Ben Werling and Zsofia Szendrei, Michigan State University.

Chemical Options for Cabbage Maggot and Leafy/Heading Cole Crops

A field with stunted and dead cabbage plants in a cabbage field managed without Lorsban. Photo: Marissa Schuh, UMN Extension.

No pyrethroids currently have a label for cabbage maggot in the non-root brassicas.  This leaves us with products like Capture and Diazinon. Verimark, while expensive, has provided good control for growers in other states.  The product is used as a tray drench before transplanting, and provides systemic control of insects for a few weeks.  This means it can take care of early season cabbage maggot as well as diamondback moth.


For information on how this affects field crops, see the University of Minnesota Crop News.

For help finding alternative chemistries and strategies in vegetables, reach out to Marissa Schuh.

For questions regarding regulatory aspects of this decision, contact the MN Department of Agriculture.


Hazzard, R. (2014, October). Cabbage Root Maggot.

Koch, R., Cira, T., Mann, R., Potter, B., & Hason, A. (2021). Environmental protection Agency's cancellation OF Chlorpyrifos Tolerances: Alternatives for management of key crop pests. Environmental Protection Agency's Cancellation of Chlorpyrifos Tolerances: Alternatives for Management of Key Crop Pests.

Foster, R., & Flood, B. (Eds.). (2005). Vegetable Insect Management. Meister Media Worldwide.

Phillips, B., Egel, D., Maynard, E., Ingwell, L., & Meyers, S. (2021). Midwest Vegetable Production Guide for Commercial Growers 2021. Purdue University.

Werling, B., Szendrei, Z., & Taylor, A. (2021, March 10). The quest for lorsban alternatives for cabbage maggot control In brassica ROOT Crops: 2018 trials.

Werling, B., & Szendrei, Z. (2021, March 10). The quest for lorsban alternatives for cabbage maggot control In brassica ROOT crops: 2019 Trials.

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