The paper reports on a project designed to evaluate the feasibility of using the GreenSeeker® RT200 mapping system to drive variable rate application (VRA) of plant growth regulators (PGRs) and defoliants on cotton in Georgia, USA. The first year's results indicate that NDVI appears to be very good tool for differentiating management zones early and late in the growing season. At mid-season, when the entire field is covered by a solid green canopy, NDVI values become saturated and are not useful for creating PGR management zones. Several confounding factors prevented us from assessing the effectiveness of using NDVI to manage PGR application. Our results indicate that NDVI seems to be an excellent tool for managing defoliant applications. In the three fields we studied, VRA resulted in 8.4% less, 2.8% less, and 1% more defoliant used. In all 3 cases, defoliation effectiveness was at least as good as or better than a producer-selected constant rate.