Jun 24, 2020Do Antimicrobial Water Sanitizers Affect Insecticide Efficacy in Produce?
This question was brought to my attention by a few PCAs and growers last August. At the time, I was not fully aware of the issue and could not provide a science-based response. Members of the Arizona Leafy Greens Marketing Agreement had just developed Food Safety Practices for using water sanitizers applied to lettuce and other leafy greens via irrigation and pesticide spray applications. Specifically, the guidelines recommend that non-potable water used for pesticide applications within 21 days of harvest must be treated with an anti-microbial sanitizer product with efficacy against E. coli and other coliform bacteria. The intent is to eliminate the potential risk from microbial pathogen contamination on harvested produce. However, no one seemed to know with any confidence whether antimicrobial sanitizers like Peroxyacetic acid (PAA) and sodium hypochlorite (NaClO) would negatively impact insecticide performance, and I wasn’t about to speculate. So, we undertook several field and lab studies to 1) measure the effects of sanitizers on the acidification of insecticide spray solutions and 2) to determine whether the addition of sanitizers effected insecticide efficacy against key insect pests in lettuce. Acidity of spray solutions is important because some compounds like Entrust, Radiant, Assail and others are unstable under acidic conditions (pH~4) and can lose residual effectiveness. Results of our study showed that PAA products (Oxidate and Jet-Ag) used at recommended rates did acidify the spray solutions, but in almost all cases not below a pH of 6. Sodium hypochlorite (Enviro Chlor) did not acidify spray insecticide spray solutions. In terms of insecticide efficacy, the results were unanimous. Results from lab bioassays and field trials with commonly used insecticides clearly indicated that the use of PAA and NaClO as water sanitizers in foliar spray mixtures did not affect knockdown and residual efficacy against worms, thrips and aphids. So, PCAs and growers should be confident in following the AZLGMA recommendations to include antimicrobial sanitizers with their foliar insecticide applications when using non-potable water. However, a few questions remain concerning the impact of water sanitizers on pesticide spraying that were not addressed in this study. We discuss those in our final report.The complete results of the study can be found in the following AILRC Final Report: Do Antimicrobial Water Sanitizers Affect Insecticide Efficacy in Desert Produce?
June 24, 2020
Name the insect pest
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu