Fig. 1. Regression of field corn yield as percent of controls of three hybrids against Corn Defoliation Progress Curve (CDPC) at five environments. Severity of defoliation (percent leaf area) was plotted against Growing Degree Days (GDD) remaining to maturity and integrated to calculate CDPC for defoliation treatments for each hybrid.

Image from Crop Management article:
Yield Loss of Corn Hybrids to Incremental Defoliation