Travis J. Lybbert, W. Douglas Gubler
The treatment of powdery mildew is among grape growers’ most important management practices. Growers’ only real hope in the powdery mildew battle is proper preventative management. Founded on the observation that powdery mildew growth is largely a function of length of exposure to different temperature ranges, the Gubler-Thomas Powdery Mildew Index (PMI) helps growers anticipate outbreaks in order to time more precisely their preventative powdery mildew treatments. The PMI can improve powdery mildew treatment timing and efficacy, yet many growers do not use this forecasting tool.