Purpose of the ratings
What is the purpose of the Bee Precaution Pesticide Ratings?
To help users make informed decisions about reducing bee poisoning when choosing and applying pesticides.
Do the ratings in this tool differ from the pollinator precautionary statement on a pesticide label?
Yes, statements on pesticide labels may differ from the ratings provided here. The environmental hazards, precautionary statements, or protection of pollinators sections of some pesticide labels may include a bee hazard warning, pollinator precautionary statement, or a bee hazard graphic. Legally, pesticide users must follow the label directions and take at least the minimum precautions required by the pesticide label and regulations. When not in conflict with the label or regulations, users may take more protective actions, such as those in the Bee Precaution Pesticide Ratings. For example, a label may allow application during flowering, but the ratings might advise against it to protect bees.
Isn't following the label enough to protect bees? Why use the Bee Precaution Pesticide Ratings?
Following the Bee Precaution Pesticide Ratings can be more protective than label instructions alone, as the tool may advise against application timings allowed by the label. Users must meet minimum label and regulatory requirements but may take more restrictive actions, such as those in the ratings, when not in conflict with the label or regulations. The label instructions may not be adequate for protecting bees:
- Bactericides, fungicides, and herbicides lacking bee hazard warnings even though some are toxic to bees.
- Synergistic effects such as tank mixes that can increase overall toxicity to bees compared to when those pesticides are applied individually.
- Effects on the brood of honey bees.
- Systemic pesticides (for example, neonicotinoids) persisting or translocating to nectar and pollen.
- Microbial or other pesticides requiring longer evaluation periods (28 to 30 days) due to their long persistence in the environment.
How to Use the Ratings
Does the rating of I, II, or III apply to all bee species or only the honey bee, Apis mellifera?
The ratings apply to honey bee (Apis mellifera) adults and brood. Ratings may help protect other bee species, but there are around 4,000 bee species in the United States and their susceptibility to pesticides may differ. For example, night applications of products rated II protect honey bees in hives but may not protect other bee species that spend the night on plants (like bumble bees) or species nesting in soil (like alkali bees). Consult resources like Best Management Practices to Protect Bees from Pesticides, Protecting Natural Enemies and Pollinators, or Conserving Bumble Bees.
To help you identify what species of bees are present at a site, consult Farming for Bees: Guidelines for Providing Native Bee Habitat on Farms and the California website of the Pollinator Conservation Resource Center. To learn what bee species are important pollinators of particular crops, click the "Find a Crop" at the top of Best Management Practices for Pollination.
What does "Toxic to honey bee brood" mean? Why do many pesticides rated I or II lack a brood toxicity check mark?
Brood (eggs, larvae, pupae) in hives is generally protected from direct pesticide exposure unless the pesticides are illegally applied directly or drift occurs. Exposure typically happens when adults carry pesticides into the hive. Pesticides rated I or II often lack brood toxicity check marks because proper field application is not expected to result in significant exposure of pesticide to honey bee brood. Worker bees exposed to such pesticides may die quickly or become unable to fly or navigate to return to the hive. Additionally, worker bees pass the collected food to nurse bees in the hive, which internally process food before it is fed to honey bee larvae or the queen. This processing can help to degrade certain pesticides and limit poisoning of the brood or queen.
What is the difference between "common name" and "trade name"? How is it relevant to pesticide effects on bees?
The common name is the standardized name of the active ingredient (for example, imidacloprid) that the Bee Precaution Pesticide Ratings are created from. The trade name is the brand name (for example, Admire) given by manufactures to a specific product and sometimes help users identify the active ingredient. Trade name products combine one or more active ingredients with other ingredients. These added ingredients help with mixing, handling, and storage but may still pose environmental or safety risks.
Labels list the active ingredients and their percentages but manufactures usually do not disclose the specific types of the other ingredients, which often make up most of the product. The potential effects of the unidentified ingredients are uncertain but can impact bees (Artz DR & TL Pitts-Singer 2015, Chen J et al. 2018, Ciarlo TJ et al. 2012, Mullen CA 2015, Mullen CA et al. 2016). Except in the case of soil-applied baits, the Bee Precaution Pesticide Ratings are based on the toxicity of the active ingredient alone because of the unknown effects of the undisclosed ingredients in trade name products.
For more information see Understanding Pesticide Labels for Making Proper Applications and the FAQ Does the Formulation Type Affect Pesticide Hazard to Bees.
Application Considerations
Does the type of formulation affect pesticide hazard to bees?
Yes. Pesticide products (trade names) with the same active ingredient (common name) can have different formulation types and other ingredients. The type of formulation may be identified on pesticide labels, sometimes by a one- to three-letter abbreviation (e.g., W or WP for wettable powder). Certain formulations can be more hazardous to bees.
- Most hazardous (small particles stick to bee hairs, get carried to hives, and may be fed to brood):
- Dusts (D)
- Dry flowables (DF) / water-dispersible granules (WDG)
- Liquids (F, L)
- Microencapsulated (M)
- Wettable powders (WP)
- Moderate hazard (direct sprays and residues can create puddles, chemigation drips or leaks occur, or systemic uptake in plants):
- Emulsifiable concentrates (EC), [ultralow volume (ULV) may be more hazardous]
- Soluble powders (SP), solutions (S), [ultralow volume (ULV) may be more hazardous]
- Systemics (soil, bark, foliar, chemigation)
- Lowest hazard (low direct exposure unless dust or water contamination occurs):
- Baits (B)
- Granules (GR)
- Pellets (P)
- Seed treatments/coatings (unless it is with systemic pesticide)
Consider using formulations that are less hazardous to bees if available for an active ingredient. There are mitigation strategies that can be used to reduce the hazard of formulations to bees. Consider the following:
- Use good management practices for chemigation
- Delay applications of systemic products until after plants have completed their seasonal flowering.
- Use Best Management to Practices to Protect Bees from Pesticides
- Prevent the formation and movement of pesticide-contaminated dust
- Consult How to Reduce Bee Poisoning from Pesticides
Why are mode-of-action (MOA) codes presented?
Mode-of-action (MOA) codes indicate how pesticide’s active ingredients affect or kill pests. MOA codes do not reliably indicate toxicity to bees.
The main purpose of the mode-of-action codes is to help users identify the appropriate pesticide rotations (alternations) to prevent the development of pesticide resistance. This helps maintain the effectiveness of pesticides.
Knowing the MOA can also help to protect bees, as certain MOA combinations increase toxicity to bees. These combinations are indicated in the other effects on bees column in the Bee Precaution Pesticide Ratings.
The mode-of-action codes are assigned by the resistance action committees:
- Fungicide Resistance Action Committee (FRAC) for fungicides,
- Herbicide Resistant Action Committee (HRAC) and Weed Science Society of America (WSSA) for herbicides,
- Insecticide Resistance Action Committee (IRAC) for insecticides and acaricides.
How are premixes (pesticide combinations) rated for bee precaution?
Premixes are formulated products with more than one active ingredient (for example, pyridaben and sulfur in the product Desperado). When at least one component of a premix is rated a I, the premix with that component automatically gets a rating of I as well. If components are rated a II or a III, the premix is evaluated using available sources and a rating is not automatically assigned.
What precautions should I take when tank mixing pesticides?
Tank mixing (combining different products in the same application) can increase bee toxicity due to synergistic effects. Bee Precaution Pesticide Ratings do not specifically evaluate tank mixes, but users should:
- Check ratings for each active ingredient considered for the tank mix.
- Avoid mixing pesticides with known synergistic effects (for example, DMI fungicides (FRAC 3) with IRAC 4A or 3A insecticides).
- Apply during low bee activity (for example, sunset to midnight) if allowed.
- Always follow label instructions for mixing pesticides.
Finding Information
Why is the pesticide I am looking for not listed?
Check the spelling. Use the common name of the active ingredient to search when possible because most trade names are not listed in the database. Common names included in the Bee Precaution Pesticide Ratings are primarily the active ingredients listed in UC IPM Pest Management Guidelines and Pest Notes. New active ingredients are rated and added only when information about their toxicity to bees becomes available.
How can I download all the results of interest to me?
Downloading listed ratings is not currently available. An alternative is to use a personal computer to view the Bee Precaution Pesticide Ratings and print or save them as a PDF from your web browser.
Why don't all herbicides have the "other effects on bees" or "indirect" note?
The "indirect" note is used only for herbicides rated III to highlight that they may harm bees by reducing food (nectar and pollen) or nesting resources. Herbicides rated I or II already indicate direct bee toxicity, so the note is unnecessary.
How Are the Ratings Established?
What are the sources of information and data used to establish pesticide ratings in the Bee Precaution Pesticide Ratings?
The Bee Precaution Pesticide Ratings are based on the authors' consideration of:
- Registration reports from government agencies that regulate pesticides.
- Open (public) literature, such as studies on bee effects published in scientific journals.
- Professional expertise, in collaboration with contributors to this tool.
The U.S. Environmental Protection Agency (EPA), Canada, and European Union pesticide-regulatory agencies receive studies on bee effects and other pesticide hazards performed on behalf of product registrants. These studies are usually considered trade secrets and are not publicly available. Authors reviewed registration reports summarizing agencies' conclusions. Canada and EU reports often cite open literature on honey bees (Apis mellifera) and other managed bee species, such as bumble bees (Bombus spp.), while EPA reports typically rely on registrant studies, focus only on adult honey bees, and do not cite open literature.
Authors critically reviewed reports and studies available to assess the effects of pesticide active ingredients (common names) and (where available) formulated products (trade names) on the adults and brood (immatures) of various bee species. Resources include:
- How to Reduce Bee Poisoning from Pesticides (2016, PNW591).
- EPA criteria for pollinator precautionary statements.
- Databases: AGRITOX (French database), Ecotox (U.S. EPA), European Food Safety Authority (EFSA), European Union Pesticides Database (EU), Health Canada, Pesticide Chemical Search (U.S. EPA).
Users can download a bibliography of reviewed reports and studies which is updated every time a common name rating is added or updated.
How did authors establish the ratings in the Bee Precaution Pesticide Ratings?
Authors use EPA’s standard criteria (like acute contact and/or oral LD50 and RT25 on honey bee adults) when available and adequate. LD stands for lethal dose and LD50 is the amount of a material that kills 50% of a group of test subjects. RT stand for residual toxicity and RT25 is the length of time after application during which residue from a material kills 25% of a group of tested bees. One microgram (µg) equals one millionth (0.000001) of a gram.
For honey bee adults if the:
- LD50 is greater than or equal to11 µg/bee, then the active ingredient is rated III.
- No bee precaution, except when required by the label or regulations.
- LD50 is less than 11 µg/bee but greater than 2 µg/bee without extended residual toxicity, then the active ingredient is rated II.
- Do not apply or allow drift to flowering plants (including weeds), except between sunset and midnight if allowed by the label. Do not contaminate water accessible to bees (for example, puddles).
- LD50 is µg/bee with extended residual toxicity, then the active ingredient is rated I.
- Do not apply or allow drift to flowering plants or contaminate water accessible to bees.
There are relatively few pesticides for which EPA reports the RT25; however authors review studies on the half-life of pesticides after applications to assess residual toxicity. Authors also review studies on the acute, chronic, and residual toxicity of many pesticides to bumble bees, honey bees, and some other species, such as alfalfa leafcutting bee (Megachile rotundata) and alkali bee (Nomia melanderi). The authors critically consider the conclusions, findings, and methods of these studies, which commonly use differing considerations and criteria than the EPA's for concluding whether the pesticides tested are toxic to bees. The review of these studies may mean an active ingredient is given a rating that suggests more restrictive usage is needed to protect honey bees. The reviews are also used to indicate if the active ingredient is toxic to honey bee brood or toxic to other bee species columns.
