Three experiments were conducted to evaluate use of 1st position uppermost white bloom (UMB) node to terminal intervals in monitoring crop development. UMB was also used to quantify "cutout" as a beginning point to evaluate effects of levels of heat unit (HU) accumulation, ranging from 450 to 1250 heat units, as crop termination timing "thresholds". UMB node to terminal intervals consistently declined as seasons progressed and boll load increased. It was suggested that this relationship may be exploited to define rates of crop development. However, crop termination timing based upon the simple UMB + HU model, as well as percent opened bolls and total heat units from planting at defoliation, provided inconsistent results for predicting lint yield. It was suggested that further refinements related to the rate of boll loading and boll opening may improve the effectiveness of the model.