Corrosion of application equipment is an issue for all plant growth regulator products containing ethephon. The pH of these products is typically below 2, which can lead to corrosion if equipment is not thoroughly cleaned. In an effort to decrease corrosion caused by these products, we have investigated the potential of adding inhibitors to the formulations. Electronic impedance measurements of the liquids on metal surfaces, such as carbon steel and aluminum, have enabled us to optimize both the type and concentration of inhibitor in the formulation. This technique provides an accurate and timely measurement, which supersedes coupon immersion tests used previously.