Bee Precaution Pesticide Ratings

  • Frequently Asked Questions (FAQs)

Questions About the Ratings

  1. What is the purpose of the bee precaution pesticide ratings?

    To help users make an informed decision about how to protect bees when choosing or applying pesticides.

  2. What is the difference between ratings in this tool and the bee protection directions on a pesticide label?

    Label statements may differ from the ratings provided here. Pesticide label statements are based on the information provided to the US Environmental Protection Agency (EPA) by pesticide registrants, the manufacturers or companies responsible for those pesticides. The source of these bee precaution pesticide ratings is explained in questions 3 to 5.

    The "Precautionary Statements" and "Environmental Hazards" sections of some pesticide labels include a bee hazard warning or pollinator protection statement. Legally, pesticide users must follow the product directions and take at least the minimum precautions required by the pesticide label and regulations.

  3. What is the source of the bee precaution pesticide ratings?

    The authors considered three principal sources of information for the ratings:

    1. How to Reduce Bee Poisoning from Pesticides - 2013. Pacific Northwest Extension (PNW) publication PNW591 (PDF).
    2. The US EPA criteria for the bee precautionary statement (PDF) on pesticide labels, the active ingredients' LD50 (≤ 2 μg/bee, > 2 to < 11 μg/bee, or ≥ 11 μg/bee) and residual toxicity to honey bee adults. Note: One microgram (μg) equals one millionth (0.000001) of a gram.
    3. The authors' consideration of pesticide active ingredients' (common names') reported effects on the adults and brood of various bee (Apidae) species.

    The authors reviewed studies published in scientific journals by pesticide researchers and summary reports from European and United States pesticide regulatory agencies that review non-public data provided to them by pesticide registrants. You can download the reports reviewed as of early 2015 by the bee precaution authors:

    Bee Precaution bibliography (PDF)

  4. Can you explain more about what "authors' consideration of" means?

    Authors used others' agreed-upon or standard criteria where they exist. As described and linked in question #3, the PNW and EPA sources 1 and 2 for adult honey bees:

    • An LD50 ≥ 11 μg/bee is considered not toxic to honey bees, so our rating for such pesticides is III - No bee precaution, except when required by the pesticide label or regulations.
    • If acute LD50 <11 μg/bee, the bee precaution pesticide rating is I or II, with exceptions such as a soil-applied bait to which honey bees would not normally be exposed. A key question in discriminating between ratings I and II is for how long after the application does the active ingredient remain toxic to bees?
    • EPA's residual toxicity criterion is RT25; once enough time passes that the pesticide kills < 25% of honey bees, it is no longer considered toxic. There are relatively few pesticides for which EPA reports they have adequate quality, residual toxicity information: Residual Time to 25% Bee Mortality (RT25) Data. Where EPA provides such data, the mortality after application is reported at varying intervals. For example, some combination of <, >, or = 1, 2, 3, 7, 8, or more hours.

    There are many published reports and studies, outside of what EPA reviewed, that report the acute and residual toxicity to honey bees and other bee species for various pesticides. Additionally, there are many published studies on the half-life of pesticides after application, which provide insight on how quickly pesticides may degrade. These information sources reviewed by the authors help to decide whether toxic pesticides should receive a bee precaution pesticide rating of I versus II.

  5. The rating of I, II, or III is for all bee species or only honey bees?

    The I to III ratings are for honey bees, Apis species, based on reports of pesticide effects on honey bee adults or brood (immature bees). Following this advice may also help to protect other bee species, but some methods for protecting honey bees differ from those for other bees. For example, for toxic pesticides that will mostly degrade within a few hours after application, the guidance "Do not apply or allow to drift to plants that are flowering, except when the application is made between sunset and midnight" (rating II), helps protect honey bees partly because they spend the night in a hive, commonly a wooden box. However, some other bee species spend the night on plants or in soil at the site.

    For more guidelines on how to avoid poisoning honey bees and wild bees, consult Protecting Natural Enemies and Pollinators. Identify what species of bees are present at the site and learn the specific ways to protect them, such as by using the "Find a Crop" link on Best Management Practices for Pollination.

  6. Why are some pesticides listed more than once under different names (e.g., sulfur and sulphur)?

    Our goal is to helps users find the bee precaution rating using the pesticide name with which they are familiar. For many pesticides more than one name is used. For example, sulfur is the common spelling in American English, but FRAC (the source of mode of action codes for bactericides and fungicides) and European Union agencies spell it sulphur.

  7. Is there a difference between the "common name" and "trade name," and if so is this relevant to pesticide effects on bees?

    Yes, the names have different meaning. Knowing this difference is important to understanding the bee precaution pesticide ratings.

    The common name identities the active ingredient (a.i.). Active ingredients are chemicals that have toxic effects on the target pest(s). For purposes such as pesticide registration (government approval to sell) and use in publications, each pesticide a.i. is assigned a nonproprietary, short, and widely-accepted common name by the International Organization for Standardization.

    The trade name (brand name) is given by registrants (pesticide companies) and used for product advertising and promotion. The product sold is a combination (formulation) of active ingredient(s) and inert ingredients. Most active ingredients are not suitable for use in their 100% pure state (e.g., may not mix well with water). Manufacturers add chemicals to improve pesticide mixing, application, safety, handling, and storage. Pesticide labels list the products' percentage of active and inert ingredients, and name all the active ingredients. Most trade name pesticides do not identify their inert ingredients; manufacturers consider their identity to be a trade secret. The type of formulation may be identified on labels, sometimes by a one- to three-letter abbreviation (e.g., W or WP for wettable powder).

    Trade name products with the same active ingredient (common name) can have different formulation types and unidentified (inert) ingredients. Given the same a.i., certain formulation types are more hazardous to bees as summarized below.

    Formulation type (abbreviation)

    Bee exposure


    dry flowable (DF), or water-dispersible granule (WDG)
    dust (D)
    flowable (F, a liquid), or liquid (L)
    microencapsulated (M)
    wettable powder (W, WP)

    Particles similar in size to pollen stick to bee hairs and can be taken to hives and fed to brood.

    Consider using formulations less hazardous to bees (below) if available for that active ingredient (common name). Avoid application during weather conditions that increase drift.

    emulsifiable concentrate (E, EC)

    Direct spray and residues

    Ultralow volume (ULV) formulations may be more hazardous than other liquid formulations.

    soluble powder (SP)
    solution (S)

    Direct spray and residues

    Ultralow volume (ULV) formulations may be more hazardous than other liquid formulations. Chemigation drips or puddles may attract bees.

    systemic (bark or soil injection or spray, or foliar application), absorbed and translocated by plant

    Some systemic insecticides may translocate to nectar, pollen, and guttation (plant exudate) droplets, and can be ingested by bees.

    Delay application where feasible until after plants have completed their seasonal flowering.

    bait (B), granular or pellet
    granular (GR)
    pellet (P)

    Applied to soil, honey bees do not pick up and are unlikely to be exposed.

    Avoid applying near known nesting beds of ground nesting bees (e.g., alkali bees).

    seed coatings

    Applied directly to seed. Ideally, bee exposure not expected.

    Can transfer to talc during planting and drift onto blooming crops or weeds or adjacent habitat.

    Adapted from How to Reduce Bee Poisoning from Pesticides, Pacific Northwest Extension publication PNW591 (PDF) and Forestry and Right-of-Way Pest Control, University of California, Agricultural and Natural Resources publication 3336.

  8. Why are mode-of-action (MOA) codes presented?

    The mode of action code refers to the way a pesticide active ingredient (common name) kills or effects the target pests and sometimes also related organisms. The main purpose of the mode-of-action codes is to help maintain effectiveness for pest control by informing users how to alternate (rotate) applications among several pesticides with different modes of action to avoid promoting pesticide resistance. The sources of insecticide and fungicide MOA classifications are IRAC (Insecticide Resistance Action Committee) and FRAC (Fungicide Resistance Action Committee), respectively. Herbicide MOA codes are developed by HRAC (Herbicide Resistance Action Committee) and WSSA (Weed Science Society of America), separately using different coding systems. The WSSA mode-of-action codes are presented at the HRAC website above.

    Knowing the MOA can also help to protect bees. Combining (mixing together) pesticides with certain modes of action results in synergism, or increased toxicity to bees. For example, pyrethroid insecticides (IRAC MOA code 3A) mixed with DMI fungicides (FRAC MOA code 3; e.g., propiconazole, tebuconazole, triflumizole) or chlorothalonil fungicide (FRAC MOA code M5), may increase toxicity to bees.

    Except for insecticides, the MOA codes are not based on pesticides' effects on bees or other insects; fungicide MOA codes refer to how fungi are affected, herbicide codes are based on how plants are affected, and so on. Even with insecticide MOA, the codes do not reliably indicate toxicity to bees. For example, if a systemic neonicotinoid (IRAC MOA 4A) application to foliage is planned, the bee precaution pesticide rating for these active ingredients is I or II, depending on the choice. The acute toxicity of neonicotinoids to bees differs by more than 100×; acetamiprid (rated II) is the least toxic to bees; clothianidin, dinotefuran, imidacloprid, and thiamethoxam are the most toxic (rated I).

  9. Can you explain the presentation style for mode-of-action code and pesticide type for premixes (pesticide combinations)?

    Premixes contain two or more pesticides. Each pesticide (common name) may be of more than one type (e.g., both a fungicide and insecticide) and so have more than one mode-of-action code. For example, the types and MOA presentation for the premix pyridaben/sulfur (Desperado) is presented below.

    The MOA codes (far right) are presented in two columns (separated by "/") in the order of the common names to which they apply. The first column (MOA codes: 21A — 21A) refers to pyridaben, the second column (UN M2 UN) is for sulfur. What the presentation may not adequately convey is that pyridaben is an acaricide and insecticide (two types, both IRAC MOA code 21A), while sulfur is an acaricide, insecticide, and fungicide (three types, IRAC codes UN and FRAC M2). Therefore, the correspondence between pesticide names, types, and modes of action sometimes is confusing.

    For certain premixes, the presentation style is more clear because the pesticides are of the same types and modes of action. For 2,4-D/dicamba/MCPP (Trimec), all three common names (active ingredients) are herbicides with the same HRAC and WSSA mode-of-action codes, O·4, where O is the HRAC mode-of-action code and 4 is the WSSA code. Note that instead of presenting the codes for 2,4-D/dicamba/MCPP as O·4/O·4/O·4, when the trade name product is in a premix of more than one active ingredient all of the same type and the same mode of action, the codes are presented only once as below.

  10. Why don't all herbicides have the "other effects on bees" or "indirect" note?

    Because a bee precaution pesticide rating of I or II already conveys concern about the pesticide, the "indirect" note is presented only for herbicides rated III. According to the available information, herbicides primarily harm bees indirectly by reducing the availability of flowering plants that produce nectar, pollen, and bee nesting material. The "indirect" note is presented so users would not get the impression that herbicides rated III are harmless to bees.

  11. Why is the pesticide I am looking for not listed?

    Make sure that you have the correct spelling. If you're searching a trade name (product brand name), most are not listed; learn and look for the common name, the name of the product's active ingredient. The names listed are primarily the common name (active ingredient) of pesticides recommended in UC IPM Pest Management Guidelines as of early 2015.

Technical Questions

  1. Why does choosing "All types" (the default) in the box near the top, then clicking "Add to list" not work?

    We're working to fix this bug. To display all of the pesticide ratings you must one-at-a-time select each of the ten types from the drop-down list in the first box. For example, select "Acaricide" in the first box, then after "All Acaricides" appears in the second box, click "Add to list" at the right. Next, select "Bactericide," "All Bactericides" appears, click "Add to list," and so on.

    Certain pesticides are of multiple types, so for example selecting only fungicides lists the acaricides, bactericides, and insecticides that are also fungicides. Because some active ingredients are of only one type, such as most herbicides, currently the only way to see all of the rated pesticides is to select each of the ten types one-at-a-time.

  2. Why doesn't sorting by trade name work, even when I select the "Trade name" button?

    The button affects only the search—whether the second drop-down box lists common names or trade names. The ratings are for the active ingredient (common name) and not for specific products (trade names), although some ratings do reflect the application type (e.g., bait formulations). Therefore the database associates, and sorts, the information according to the pesticide common name.

  3. How can I clear the display list of all the pesticides I previously selected?

    Click near the top of the table to the left of "Common name (example trade name)" to delete all listed pesticides at once.

  4. How can I download all the results of interest to me?

    Downloading listed results is currently not available.

Learn about how to use the Bee Precaution Pesticide Ratings video. [3:05]