New California Regulations Help Reduce Runoff of Pyrethroid Insecticides into Urban Waterways

SACRAMENTO, Calif. – The interim results of a new study conducted by the Pyrethroid Working Group (PWG) indicate that new regulations can reduce potential pyrethroid insecticide runoff from structural pest control applications by as much as 50 fold, PWG officials announced today.

The results are important because today the new Surface Water Protection Regulations adopted by the California’s Department of Pesticide Regulation (DPR) go into effect. These regulations will apply to all commercial applicators, including maintenance gardeners and 17 types of pyrethroids used by pest control businesses. Pyrethroids represent a category of ingredients used in insecticides to control ants, cockroaches, termites and other important residential pests.

“Our study appears to validate the value and relevance of the new restrictions,” said Fred Pearson, Chair of the PWG, an industry group comprised of the nation’s leading pesticide manufacturers. “By adhering to the new requirements, pest control operators can take positive steps that in all likelihood will help keep pyrethroid insecticides out of waterways and allow the continued safe use of these effective pest control technologies.”

In many cases, the new DPR regulations narrow the application of pyrethroid insecticides to spot, pin stream and crack and crevice treatments. The guidelines also prohibit outdoor application when it is raining, or to areas with standing water that may empty into storm drains.

PWG announced today that it is also developing a new online video to help pest control professionals better understand the new requirements.

“We are working with various stakeholders to develop a demonstration video that will be available soon,” said Pearson. “It is intended to show how changing application methods can reduce runoff. We want to show the link between the findings of our study and the new application methods and regulations.”  PWG expects to post the video within the next few weeks at

The Research Study
The project was designed to simulate pesticide applications and runoff in a real world environment. The goal was to identify the major pathways for insecticide runoff following applications to suburban residences using historic application practices as well with revised practices (i.e., those currently being specified on product labels and required under the DPR regulations). Toward that end, the PWG built a full-scale test facility in Central California. Six full-scale replicate house lots mimicked front lawns and house fronts of California residential developments and included stucco walls, garage doors, driveways, sloping lawns and residential sprinkler systems. Each lot also included a rainfall simulator to generate artificial rainfall events.
Different pyrethroids were applied to five surfaces—driveway, garage door and adjacent walls, lawn, lawn perimeter (grass near the house walls), and house walls. The volume of runoff water from each house lot was measured, sampled, and analyzed to determine the runoff from each surface during each irrigation and rainfall event.
Applications to three of the house lots were made using historic application practices. The remaining lots received applications according to revised procedures – those currently specified on product labels and required under the upcoming DPR regulations.

The Findings
While DPR is still in the process of reviewing the study, PWG officials say the research data demonstrate that there is a direct correlation between the new DPR restrictions and a significant reduction in the amount of insecticide runoff.

Results from the house lots using the historic application procedures demonstrated that applications to driveways, garage doors and adjacent walls next to concrete and above driveways account for greater than 99.5 percent of runoff losses of residential applications of pyrethroids. Runoff was associated with significant rainfall events, not lawn watering/irrigation.

Following the application practices required by DPR’s new regulations resulted in a 50- fold overall reduction in runoff when compared to prior practices. These changes should dramatically reduce the potential for runoff, especially from garage doors and the pavement in front of garage doors while still providing the desired pest control.

“This issue is a good example of government and industry coming together to do the right thing,” said Pearson. “Our research and video are aimed at making sure pest control operators have the tools to use our products in the most prudent and environmentally sensible way possible.”

The Pyrethroid Working Group (PWG) is an alliance of companies that manufacture pyrethroid insecticides and work together to address a wide range of issues specific to pyrethroids, a class of effective and widely used active ingredients for general pest and termite control.