SYMPOSIA PAPER Published: 01 January 1993

Controlling Microbial Growth in Aqueous-Based Pesticide Formulations


Flowable pesticides contain dispersants and thickeners that can support the growth of microorganisms. Even limited microbial growth in a flowable pesticide can destroy the integrity and performance of the product. Biocides are typically added to flowables to prevent microbial growth. Because an exemption from tolerance is required for any biocide added to a formulation, the list of products available to the formulator is extremely limited. The newest biocide chemistry to receive EPA exemption from tolerance for pesticide preservation is methylchloroisothiazolone (MCI). The efficacy of MCI in pesticide products was determined with microbial challenge tests. Results indicated that MCI kills microorganisms as effectively as formaldehyde, but at significantly lower concentrations. MCI is compatible with other inerts, non-phytotoxic (even at 50 times use level), and biodegradable. It is also stable and effective over a wide range of pH. Stability and efficacy tests have indicated that flowable pesticides that are aggressive to 1,2 benzisothiazolin-3- one can be effectively preserved with MCI biocide.

Author Information

Haack, TK
Warwick, EF
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Developed by Committee: E35
Pages: 105–115
DOI: 10.1520/STP20186S
ISBN-EB: 978-0-8031-5221-2
ISBN-13: 978-0-8031-1439-5