On March 21, 2019, the U.S. Environmental Protection Agency (EPA) announced it was updating its Residual Time to 25% Bee Mortality (RT₂₅) Data Table with information it has collected since the table was first published in 2014.  EPA states that the “RT₂₅ data help farmers and beekeepers know about how long a specific pesticide may remain toxic to bees and other insect pollinators following foliar application to crops,” and the new data “reflect the results of studies the agency has analyzed as part of [its] routine pesticide regulatory activities.”  One example that EPA provides regarding how this new data will work is that farmers can now “choose pesticides that quickly lose their toxicity to bees,” and that applying the products in the evening “helps ensure that by morning the pests have been dealt with and blooming crops are safe for bees.” 

EPA states that RT₂₅ values are a function of a number of factors including application rate, physical-chemical properties, dissipation, crop, and pesticide formulation.  The values provided were compiled from registrant-submitted data submitted to fulfill the data requirement for Honey Bee (Apis mellifera) Toxicity of Residues on Foliage study (OCSPP Guideline 850.3030).  EPA states that the honey bee toxicity of residues on foliage study “is a laboratory test designed to determine the length of time over which field weathered foliar residues remain toxic to honey bees, or other species of terrestrial insects” and, depending on the chemical tested, “either the technical grade active ingredient or a specific formulation was tested using either the honey bee, alfalfa leaf cutting bee, or alkali bee.”  The data table lists the test material, the species tested, and the plant species on which residues were aged.

EPA plans to update the table annually as it collects additional data going forward.  More information on EPA’s actions intended to protect pollinators is available on EPA’s website.

Commentary

In addition to providing the residual toxicity values, the table also illustrates the wide range of toxicity values among the various pesticides.  RT₂₅ times for the different active ingredients can range between a few and over 500 hours to reach the RT₂₅ threshold.  Even different formulations using the same active ingredient can have a significant difference in toxicity values.  This illustrates the importance of reading the specific label instructions for a pesticide, even one that might be generally familiar to the user.

EPA’s publication of this information online also imposes a duty for EPA to continually update the table, especially to capture any changes in the information appearing in an earlier listing of the data.  If, upon further review or later data submissions, there are changes to the table for a product, EPA will need to alert users to potentially important changes in the information.  Again, this illustrates the need for reading the label for each pesticide at the time of application, since some important information may have changed.