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    Evaluation of the Rain Fastness of Pesticide Formulations Using Simulated Leaf Surfaces with a Visual Rating System

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    Rain tenacity of formulations of contact fungicides is an important property and should be evaluated during early stages of formulation development. The rain tenacity of these formulations on foliar and fruit surfaces can affect their overall performance (efficacy) and the number of spray applications required for effective season long disease control. A test procedure has been developed which is useful for screening formulation candidates quickly and accurately to select the most effective candidate to advance to greenhouse or field evaluation. The method consists of applying and drying test formulations on small panels which simulated leaf surfaces. The panels are visually rated after subjecting them to a simulated rain. The presented test procedure was validated using a suspension concentrate standard and an experimental formulation of chlorothalonil. The visual ratings were corroborated with gas chromatographic analyses to determine the amount of residue remaining on the panels and banana leaf segments. There was a high degree of correlation between residues retained on the simulated leaf surfaces and the banana leaf segments with both formulations. There was also a strong correlation between residue ratings based on visual observations and actual residue retained as determined by solvent extraction and gas chromatography analysis. It was concluded that this test procedure provides a quick and inexpensive means for obtaining accurate and reliable data on the foliar rain fastness of formulations which form solid suspensions upon dilution with water.


    rain tenacity, rain fastness, chlorothalonil, fungicides, gas chromatography, pesticides, formulation

    Author Information:

    Lopez, HB
    Formulations Development Chemist, Formulations Development, ISK Biosciences, Houston, TX

    Hua, TQ
    Analytical Chemist, Quality Control Laboratory, ISK Biosciences, Houston, TX

    Committee/Subcommittee: E35.22

    DOI: 10.1520/STP16042S