Slowing and Combating Pest Resistance to Pesticides
Pesticides can be used to control a variety of pests, such as insects, weeds, rodents, bacteria, fungi, etc. Over time many pesticides have gradually lost their effectiveness because pests have developed resistance – a significant decrease in sensitivity to a pesticide, which reduces the field performance of these pesticides.
EPA is concerned about resistance issues. We believe that managing the development of pesticide resistance, in conjunction with alternative pest-management strategies and integrated pest management (IPM) programs, is an important part of sustainable pest management.
- What EPA is doing
- General recommendations related to resistance management in agriculture
- Related regulatory information
- Additional resources
To address the growing issue of resistance and preserve the useful life of pesticides, we are embarking on a more widespread effort and set of activities aimed at combating and slowing the development of pesticide resistance. Our effort includes releasing and requesting comment on two Pesticide Registration Notices (PRNs) that focus on strategies to combat or slow pesticide resistance.
PRN 2017-1, Guidance for Pesticide Registrants on Pesticide Resistance Management Labeling, revises and updates PRN 2001-5. PRN 2017-1 applies to all conventional, agricultural pesticides (i.e., herbicides, fungicides, bactericides, insecticides, and acaricides).
The updates in PRN 2017-1 focus on pesticide product labels. These updates are aimed at improving information about how pesticide users can minimize and manage pest resistance.
PRN 2017-1 updates PRN 2001-5 with the following three general categories of changes:
- additional guidance to registrants, and a recommended format, for resistance management statements or information to place on labels;
- references to external technical resources for guidance on resistance management; and
- updated instructions on how to submit changes to existing labels in order to enhance resistance-management language.
PRN 2017-2, Guidance for Herbicide Resistance Management Labeling, Education, Training, and Stewardship, applies to herbicides only. PRN 2017-2 communicates the Agency’s current thinking and approach to addressing herbicide-resistant weeds by providing guidance on labeling, education, training, and stewardship for herbicides undergoing registration review or registration (i.e., new herbicide active ingredients, new uses proposed for use on herbicide-resistant crops or other case-specific registration actions).
This guidance is part of a holistic, proactive approach to slow the development and spread of herbicide-resistant weeds and to prolong the useful lifespan of herbicides and related technology.
PRN 2017-2 also provides 11 elements focused on labeling, education, training and stewardship strategies. Herbicides posing the least risk of developing herbicide-resistant weeds will have the fewest resistance management elements, and herbicides that pose the greatest risk of resistance will have the most elements.
We are focusing on more holistic guidance for herbicides first because:
- they are the most widely used agricultural chemicals;
- no new herbicide mechanism of action has been developed in last 30 years; and
- herbicide-resistant weeds are rapidly increasing.
Biopesticides and Resistance Management
Biopesticides are compounds derived from biological sources, such as plants, bacteria, fungi, or viruses. Many of these products are used in organic crop production, and they can be included in resistance-management programs by both conventional and organic growers.
Regulation of Plant Incorporated Protectants
Plant-incorporated protectants (PIPs) are pesticidal substances produced by plants and the genetic material necessary for the plant to produce the substance. PIP crops are plants whose genomes include foreign genes that code for compounds that have pesticidal activity. For example, PIP crops such as corn and cotton have genes for the production of Bacillus thuringiensis (Bt) endotoxin (derived from the bacterium Bacillus thuringiensis). EPA registers and regulates PIPs (the expressed protein and its genetic material) as pesticides under FIFRA but does not regulate the plant itself.
Regulatory oversight includes human health and environmental fate risk assessments as well as resistance-management risk evaluations. According to the Code of Federal Regulations (Title 40, Part 174—Procedures and Requirements for Plant-Incorporated Protectants) the characteristics of PIP crops, such as their production and use in plants, their biological properties, and their ability to spread and increase in quantity in the environment distinguish them from traditional chemical pesticides. Therefore, PIPs are subject to different regulatory requirements and procedures as compared to traditional chemical pesticides.
A major component of EPA’s regulation of PIPs is the requirement for an in-depth insect resistance management (IRM) strategy. The primary component of IRM for Bt PIPs is the use of refuges to reduce selection pressure for resistance. A refuge typically consists of non-PIP crops that are planted to serve as source of susceptible insects to mate with any resistant insects arising from the PIP crop. Types of refuges include:
- Block refuge (a dedicated non-PIP portion of the PIP crop).
- Seed blends (non-PIP refuge seed is comingled with PIP seed in the same seed bag).
- Natural refuge (weeds, wild hosts, and other crops that produce susceptible insects, used for Bt cotton PIPs).
Other aspects of IRM for PIPs include IPM-based stewardship, resistance monitoring, grower education, compliance monitoring (for refuge deployment) and mitigation strategies in the event of confirmed resistance.
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The goal of successful resistance management is to reduce populations of pests, whether they are resistant or susceptible to pesticides. The general recommendation when using pesticides is to alternate or tank-mix pesticides of different chemistry and modes of action. This recommendation is based on the theory that the likelihood of a population developing resistance to two or more pesticides, each from a different chemical group with different modes of action, is significantly less than the likelihood that a population could develop resistance to only one of the pesticides. Therefore, individuals in the pest population resistant to one of the pesticides would be killed upon exposure to the (different) partner pesticide. However, there are some cases where even this strategy has resulted in resistance to both pesticide groups.
The best way to avoid resistance is to use IPM strategies to prevent the increase in resistant pest types, such as:
- Rotating crops to reduce the use of the same pesticides season after season.
- Reducing nutrient sources such as plant stubble that can harbor pathogens and insects.
- Using grazing animals in some cases to reduce (some) weed populations.
- If available, using scientifically verified methods to sample pest populations and correlate them to economic estimates of crop damage before applying pesticides.
- Timing chemical applications when the pest is most susceptible (e.g., waiting for insect emergence or using preventive fungicide applications when weather conditions appear to be conducive to disease development).
- Scouting before and after pesticide application to correctly identify the pest and to determine if the application provided effective control.
Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) the Agency has the responsibility to register and regulate pesticides. Under this authority, pesticide resistance may be considered in the risk-benefit decision-making process.
In Guidance on Final FIFRA Section 6(a)(2) Regulations for Pesticide Product Registrants, any substantiated incidents of pest resistance for any regulated pesticide product must be reported to the Agency. This reporting requirement is in accordance with FIFRA Adverse Effects Reporting Section 6(a)(2), which requires pesticide product registrants to submit adverse-effects information about their products to EPA.