When a plant growth regulator is applied, it blocks hormone synthesis. The normal hormone synthesis will resume after the growth regulator is metabolized, or broken down, by the plant. The speed of growth regulator metabolism is strongly influenced by temperature. Therefore, the calendar based re-application interval is only a crude approximation of how long the growth regulator will work. It may work for only one week in the summer, or six weeks in the fall depending on temperature.
Based on five years of research, we’ve developed a growing degree day for accurately determining the proper re-application interval for trinexapac-ethyl and paclobutrazol for creeping bentgrass putting greens. Different plant metabolize growth regulators at different rates, so these models are only valid for creeping bentgrass.
Additional info regarding the growing degree day models for plant growth regulators: