PENNSYLVANIA TURFGRASS: Ben McGraw, Ph.D.

There have been more changes to the turfgrass insecticide landscape over the last 12–18 months than any other time that I can remember in my career. Many of the changes have been good ones for turfgrass managers in Pennsylvania (and much of the country) as new active ingredients have been registered, including a new anthranilic diamide (tetraniliprole (IRAC = 28), Tetrino®, Bayer), a combination product (alpha-cypermethrin (IRAC = 3A) + dinotefuran (IRAC = 4A), Alucion®, BASF) and an insect growth regulator (novaluron (IRAC = 15), Suprado, QualiPro). On the other side of the turfgrass insecticide ledger, it is likely that older chemistries will be phased out of the market as federal agencies conduct periodic reviews of registrations. In February 2022, the Environmental Protection Agency (EPA) announced that it would be banning agricultural uses of the organophosphate chlorpyrifos (IRAC = 1B), leaving many to wonder about its continued use in turfgrass. A total ban of chlorpyrifos has already occurred in New York and Maryland, which has caused some confusion as to its use in other states. I admit that I was confused and did not fully understand the changes at the federal and state level, and therefore set out on a mission to better educate myself. This article is not an endorsement of chlorpyrifos, but rather a means to help inform readers of what to expect in the short-term regarding its use in turfgrass.

Organophosphates

The insecticidal properties of organophosphates have been known since the mid-1800s with the first compound (tetraethylpyrophosphate) being synthesized in 1854. Organophosphates work by inhibiting an enzyme (acetyl choline esterase) in nerve cells. Acetyl choline esterase degrades the chemical neurotransmitter that causes a nerve impulse that would otherwise turn the impulse into muscle movement. The delivery of an organophosphate into the insect’s body essentially stops the enzyme’s normal functioning, the neuron fires repeatedly, which leads to muscle overuse and tetany, and eventual death. Human nerve cells also possess acetyl choline esterase and therefore can suffer adverse acute and/or chronic reactions when exposed to organophosphates. It is also for this reason that many organophosphates active ingredients were discovered. Organophosphates were used as insecticides in the 1930s, though thousands of compounds were developed in Nazi laboratories during this period to discover nerve toxins that could be used on the battlefield. Organophosphates that demonstrated promise in insect control were made available to the public for agricultural and residential use after World War II.

Organophosphates in turf management

Several organophosphates have been used to control turfgrass insect pests over the last 70 years though only three active ingredients (acephate, trichlorfon, chlorpyrifos) are commonly used today. General characteristics of organophosphates include contact activity, limited mobility (as they bind to organic matter), and relatively low residual activity or half-life within the soil. Subtle differences can be observed between organophosphate active ingredients, leading to slight changes in their use. For example, the biggest difference between all three organophosphates used in turfgrass is that trichlorfon (e.g. Dylox®, Bayer) has much, much greater solubility than acephate and chlorpyrifos which are relatively insoluble. Trichlorfon solubility allows it to move through the soil profile despite having high binding potential like the other organophosphates. Therefore, it can be used as a curative white grub larvicide, whereas the other two actives are relatively insoluble and likely to bind to thatch and organic matter before reaching the target site. Therefore, the primary use for most organophosphates in turfgrass insect management is limited to contact control of surface-active insects.

Regulatory review

Chlorpyrifos, which became a mainstay for agricultural and household use after its discovery in 1965 due to its persistence and relative safety compared to others within the class, has been reviewed by the EPA multiple times. The EPA reviews the registration of any pesticide every 15 years and considers new scientific findings in the continued registration of the active ingredient.

The EPA mandate is to only register a pesticide “when it determines that it will not cause unreasonable adverse effects on humans or the environment, while considering the economic, social, and environmental costs and benefits of the use of the pesticide (Federal Insecticide, Fungicide, and Rodenticide Act).” Several organophopshates developed around the same time as chlorpyrifos have been banned by the EPA for their potential adverse effects on human health, though the phase-out process can be lengthy. The phase out of diazinion began in 1988 after a link between its use and massive bird die-offs in open spaces (including golf courses) was established. However, the last sale of diazinon was not until in 2004. Phasing-out of certain uses of chlorpyrifos has also been a lengthy process. Changes to the Food Quality Protection Act (FQPA) in 1996 set a more rigorous safety standard to reduce children’s exposures to pesticides, which in turn led to the voluntary elimination, phase-out, or modification of certain uses of chlorpyrifos in 2000. Other reviews have occurred in the last 22 years, including changes to labels to protect workers (2002, 2012) and periodic human health risk assessments as new information becomes available (2011, 2014, 2016, 2020).

Sifting through the EPA documents pertaining to the EPA registration reviews can be dull, but five years ago things started to get interesting. In 2017, environmental advocacy groups brought forth a petition to revoke all chlorpyrifos tolerances and cancel all chlorpyrifos registrations based on the 2014 human health assessments. It has long been known that chlorpyrifos exposure can be more harmful during development than in adulthood and that these impacts to the developing brain can contribute to behavioral abnormalities. Despite this, the petition was denied based on the need for more time to examine the science addressing neurodevelopmental effects. This ruling was challenged in the U.S. Court of Appeals for the Ninth Circuit, which hears cases pertaining to civil and criminal matters that fall under federal law. In 2021, the Court found that the EPA’s denial was arbitrary and issued a final rule revoking the tolerances unless the EPA could show the tolerances were safe….otherwise, they would need to modify or cancel food-use registrations for chlorpyrifos. In February 2022, EPA issued letters to companies with chlorpyrifos registrations indicating that they will proceed with canceling the registered food uses.

It is important to note that these rulings have implications for food-use registrations as many non-agricultural/non-food uses of chlorpyrifos remain registered. I think much of the assumed deregistration of chlorpyrifos in Pennsylvania turfgrass has come from the media attention given to the cancellation of uses pertaining to agricultural uses without emphasizing allowance for certain systems. Some confusion may arise from the fact that our neighbors in New York and Maryland have total bans on chlorpyrifos as well, which may have led to regional distributors discontinuing sales within turfgrass. Even with chlorpyrifos registrations in place in Pennsylvania turfgrass, this does not pertain to all turfgrass sites. According to the Pennsylvania Department of Agriculture, chlorpyrifos has been prohibited for residential turf sites within the Commonwealth. The Department has not taken any further action to restrict use of chlorpyrifos on golf courses, sod, and industrial or highway turf areas.

What next?

I wrote this article because I had assumed that chlorpyrifos bans in turfgrass were imminent and that Pennsylvania, much like neighboring states, had begun phasing-out chlorpyrifos. I had mentally moved on to a life without the active ingredient. For some (maybe most) this is not too hard to imagine. The good news is that better (i.e. more efficacious, more selective/less broadly toxic) alternatives to chlorpyrifos exist for almost every turf insect situation. The major exception to this rule happens to be one of the greatest challenges in turfgrass insect management. The management of pyrethroid-resistant adult annual bluegrass weevils (ABW) is hindered by a limited number of effective options. In this case, a single, well-timed application of chlorpyrifos against emerged, overwintering adults in spring is currently recommended to reduce some of the egg layers and synchronize larval development. Secondly, I am quite optimistic that solutions will be developed (and registered) for this issue in the very near future.

It is not difficult to recognize that there are inherent issues with many early generation insecticides like organophosphates and the adverse neurodevelopmental effects to agricultural workers exposed to chlorpyrifos and their offspring should cause pause. The EPA will continue to review chlorpyrifos registrations in the future and it is likely that the situation in Pennsylvania could change quickly. So, though this article may be helpful to some for-product selection in the short-term, I think it wise to plan for alternative approaches in the future whether mandated or not. The Turfgrass Entomology Laboratory is committed to working on this issue and it is my hope to be reporting on our adult ABW control research in the near future.

For more information and documents related to the review process:

EPA: https://www.epa.gov/ingredients-used-pesticide-products/chlorpyrifos

The post Pennsylvania Turfgrass Council – Chlorpyrifos: The Uncertain Future of the Controversial Insecticide and Implications for Turfgrass Management appeared first on The Turf Zone.