Pesticide Decline Study in Blueberries to Facilitate Export

By Camille Holladay, Owner & Lab Director,
Synergistic Pesticide Laboratory, LLC, OBC Chair

The US EPA establishes the tolerance for pesticides allowed on crops in the United States, which are known as Maximum Reside Levels (MRLs) in other countries. Exporting to markets with MRLs that are lower than the US tolerance can pose a risk for producers or render a plant protection product useless. MRL violations can be costly to a shipper and cause industry wide issues if multiple violations rack up. It is in everyone’s best interest to comply with MRLs.

Camille Holladay, Owner & Lab Director, Synergistic Pesticide Laboratory, LLC, OBC Chair

Growers need as many tools in their toolbox as possible. Pesticides degrade differently depending on several factors such as their chemistry and environmental conditions. Knowing how pesticides behave can help avoid MRL violations and keep the tools industry currently has. Over the past 10 years, Synergistic Pesticide Lab has worked with research partners to provide data needed to export blueberries. First, data was generated for SWD insecticides on blueberries in Washington, Oregon and Michigan over three years. Then, another three-year fungicide trial was conducted in Washington. 

Last year was the third and final year of a Technical Assistance for Specialty Crops (TASC) funded grant secured by the USHBC to develop decline data for pesticides 1) not included in previous studies; 2) newly registered; or 3) pending registration. We have generated new decline curves for 32 active ingredients representing 30 commercial formulations of insecticides, miticides and fungicides commonly used in blueberry pest management. The main goal of the study was to create an MRL guidance chart using the decline curves that will quickly show how much time is needed to safely use a product and comply with MRLs for a particular market, thus empowering the decision-making process for growers and shippers. Another goal of this project is to use the data to support requests to raise MRLs in various countries, opening export markets for blueberries and allowing for greater diversity in pesticides used. A great amount of cooperative work is done behind the scenes by the Oregon Blueberry Commission, Washington Blueberry Commission, US Highbush Blueberry Council, North American Blueberry Council, IR-4 and Bryant Christie, Inc. to harmonize MRLs.

Data for this most recent project was collected from locations in Eastern and Western Washington, Oregon, Michigan, Coastal and Central California. The different locations, varieties and application methods are designed to be representative of real-world conditions for blueberry growers. All treatments were replicated four times with samples taken once dry on the day of application, then at 1, 3, 5, 7, 14 and 21 days after treatment (DAT). One location also took samples at 28 DAT in 2020. All samples were frozen immediately following collection and either shipped overnight or hand delivered to the laboratory.

Upon receipt at the lab, samples were homogenized and stored frozen until extraction and cleanup. Analysis was done by LC/MS/MS and GC/MS/MS with Limits of Quantitation set as low as possible to mirror MRLs. The data was calculated, then averaged across the replicates resulting in points along the decline curve of concentration over time with a 95 percent confidence interval for each pesticide at each location and each year. Pre-Harvest Intervals (PHI) were indicated on the x-axis and the US Tolerance (MRL) on the y-axis of the graphs for reference.

The stop light MRL guidance charts list top export markets and provide the following color-coded guidance at each DAT:  RED means that the product should not be used during this time either because of EPA label restrictions or due to a high risk of exceeding MRLs for a given market. YELLOW means that the product should be used with caution during this time given all the variables (e.g. tank mixes, application method and calibration, use of adjuvants, environmental conditions and post-harvest handling) that can impact the time it takes for a residue to degrade in order to meet the MRL for a given market. GREEN means that the product is likely to be safe for use at this time with low risk of residue remaining at harvest that would exceed MRLs for a given market.

The USHBC has made the final report available online that includes more details of this project along with the decline curves, MRLs and the resulting stop light MRL guidance for each of the products that are currently registered. 

Click here to view the USHBC Residue Decline Curve

Additionally, here is a link to the comprehensive MRL guidance charts for all pesticide decline work done in blueberries from 2013 to 2022. 

Click here to view the MRL Guidance Charts

It has been a great honor for us at Synergistic Pesticide Lab to participate in these studies and we are excited to share the final results. This information will be maintained as MRLs change and products are registered. Hopefully, the charts will become greener over time as MRLs are harmonized internationally due to the efforts of those working on behalf of the US blueberry industry.

A special thanks to our cooperators and sponsors: Alan Schreiber, Agriculture Development Group, Inc; Dani Lightle, Oregon State University; Rufus Isaacs, Michigan State University; Vishal Shinde, Ag Metrics Group; USDA Technical Assistance for Specialty Crops (TASC); Renata Dalton, US Highbush Blueberry Council; North American Blueberry Council; IR-4 Project; Bryant Christie, Inc; Oregon Blueberry Commission; Washington Blueberry Commission; and private contributions from Oregon blueberry growers.

Synergistic Pesticide Lab is a family owned and operated lab specializing in pesticide residue analysis with over 45 years of combined experience. We provide MRL and agronomy testing in addition to conducting research projects benefitting multiple agricultural industries.