Differences in canopy architecture alter the canopy microclimate (Baldocchi et al., 1985), and hence the physiological responses of the crop ecosystem, including the plant and insect populations within that ecosystem (Buschman et al., 1984; Hutchins and Pitre, 1987). Okra-leaf cultivars of cotton have been found to be successful under certain planting regimes, such as narrow-row (Heitholt et al., 1992). One significant difference in okra-leaf and normal-leaf cotton canopies is the difference in penetration of light (photon flux density, PFD) into the canopy as a function of row-spacing and leaf type (Sassenrath-Cole and Heitholt, unpubl.). These differences in PFD penetration are dependent on the leaf area index (LAI) of the crop. The efficacy of insecticide application also depends on the canopy architecture (Hutchins and Pitre, 1984). In order to determine the potential penetration of insecticide into cotton canopies as a function of canopy architecture, we varied the canopy architecture using various leaf types and row spacings and determined distribution of spray within the canopy. Okra-leaf and normal-leaf near isolines of an experimental cotton cultivar (24-8ne, Meredith and Bridge, 1977) were planted in standard row (40") and narrow row (20") in Starkville, MS on May 19, 1993. Spray penetration into the canopy was determined using fluorescent dye sprayed on string held at different heights within the canopy. A ground spray rig was used to spray the dye. The amount of dye deposited on the strings was measured spectrophotometrically. Leaf area index within the canopies were determined non-destructively using a LiCor LAI 2000 Plant Canopy Analyzer. We found differences in spray penetration between the four treatments (leaf type and row spacings). The depth of spray penetration was related to the LAI at the given canopy height.