Tank Mixing Disinfectants and Insecticides: Is it Worth the Risk?

By MWI Technical Services |

We ask a lot of our insecticides in live animal production. Our expectation is that they work well to eliminate insect pests, yet not be toxic to or bioaccumulate in humans or animals, be stable enough to maintain residual efficacy, and not be persistent in the environment.


 

Thus, these molecules are designed to have very specific solubilities and both chemical and physical stability, and yet be able to be broken down at some point through natural mechanisms.

A similar challenge exists for the somewhat limited selection of disinfectants available for animal housing and processing facilities. The expectation by the customer is to have a chemical aggressive enough to quickly kill a wide variety of biological pathogens (vegetative bacteria, spores, viruses, fungi, etc.) on diverse surfaces, yet be relatively safe for humans to apply and for animals to be exposed to any dry residues. Some disinfectants even have a “residual” effect while others can maintain efficacy in a wide array of pH values, with minimal impact on wastewater microbes and minimal impact on the environment.

The proper use of insecticides and disinfectants provides value to the end user by controlling direct and vector-derived pathogen exposure, protecting physical structures, and improving animal performance. The investment in these two biosecurity chemical categories is not insignificant, but neither is the labor needed to apply them. Add to this the quick turnaround times often needed to maintain production rates and you get a temptation to use any reasonable shortcut available for production managers. One shortcut that may have a significant impact on your facility is the combination of insecticides and disinfectants in the same tank, sprayed after either “dry cleaning” (the mechanical removal of debris without water, e.g. brooms, shovels, skid-steers, blowers, etc.) or after washing with a detergent and drying.

Geden et al. 1987 and Watson et al. 2008, two different sets of researchers at North Carolina State University asked essentially two questions: 1) what happens to the killing ability of an insecticide against house flies (Musca domestica) (F) and/or litter beetles (Alphitobius diaperinus) (B) if a disinfectant is added to the insecticide [Table 1], and 2) what happens to the chemical disinfection power against Salmonella Typhimurium (Sal), Staphylococcus aureus (St), and/or Pseudomonas aeruginosa (P) if a given insecticide is added to the tank [Table 2]?

The two tables show the combined results of those two studies. Note: the studies were not identical in design, did not measure exactly the same endpoints, and measured popular chemicals used at the time of the experiments. The summary provided in this article represents qualitative assessment of the original published data and does not describe dilution rates, percent inactivation, pH, or statistical differences between control and treatment groups.

The take-home lesson from the research seems fairly clear. First, there are almost no combinations of chemicals that result in zero impact on the efficacy of either the disinfectant or the insecticide (e.g. Tris nitro/formalin/quat + dichlorvos and tetrachlorvinphos). There also does not appear to be any clear, single predictive factor associated with the study; the exception may be that sometimes factors such as pH incompatibilities may play a strong role in predicting compatibility [Table 3]. In general, it should be assumed that a mixture of any two chemicals in the same tank will partially or completely inactivate either the disinfectant, the insecticide, or both when used at normal and sometimes double label rates.

The best policy for cleanout is to adhere to labels for proper dilution rates, let the disinfectant chemicals dry between applications, and apply your (residual) insecticide after the disinfectant is applied and dried. Also use the tables to look for glaring chemical incompatibilities as you rotate insecticides and disinfectants during the year.

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About the Author

MWI Technical Services

Entomologist
MWI Animal Health
Dr. McDonald is a member of MWI's Technical Services groups. As a team, this group provides our clients with targeted expertise in integrated pest management, proactive disease/pathogen and performance management, animal drinking water quality improvement, biosecurity, and cleaning and disinfection. 
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