The stay-green trait in maize has become a key target in breeding programs aiming to enhance grain yield (GY) stability under adverse environmental conditions. Characterized by delayed leaf senescence during grain filling, the stay-green phenotype maintains photosynthetic activity and canopy integrity longer, increasing radiation interception and biomass partitioning to kernels. In tropical environments, where high temperature and erratic rainfall are frequent, the ability of a hybrid to maintain a green canopy during reproductive stages is particularly advantageous. Remote sensing technologies, especially those based on unmanned aerial vehicles (UAVs), provide a rapid, non-destructive, and high-throughput means to quantify canopy dynamics. Vegetation indices (VIs) derived from RGB images, such as the Visible Atmospherically Resistant Index (VARI), offer a cost-effective alternative to multispectral methods. The VARI index has shown promising results in distinguishing green vegetation from soil background, especially under field conditions where spectral contrast may be subtle. This study aimed to quantify green canopy cover (GCC) of maize hybrids using VARI, across different phenological stages, and to investigate its relationship with GY. The objective was to evaluate whether VARI-based green cover could serve as an effective phenotyping tool for selecting high-performing stay-green hybrids adapted to subtropical low-input systems. The experiment was conducted at the Experimental Station Ilha Barra do Pomba, Itaocara–RJ. Eight maize hybrids were used: the interpopulation hybrids UENF 506-11 (H1) and UENF 506-16 (H2), both grain-type; UENF MSV 2210 (H3), suitable for silage and green corn; and UENF MS 2208 (H4), for silage. Commercial hybrids included BM 207 (H5) and AG 1051 (H8) (double hybrids); and LG 6036 (H6) and 30F35R (H7) (single hybrids). Due to replanting, H5 was excluded from statistical analyses. The design was a randomized complete block with four replicates (32 plots). Each plot had four 4-m rows (0.70 m between rows; 0.20 m between plants), totalling 80 plants. A DJI Mavic 2 Pro UAV with a 20 MP RGB camera was used to collect aerial images at 80 m (2 cm GSD). Flights were conducted at 0 (emergence), 19 (V2–V3), 34 (V3–V4), 91 (R2), 98 (R3–R4), 112 (R4–R5), 119 (R5–R6). Figure 2 illustrates the orthophoto captured at 119 DAP. VARI was calculated as (G−R)/(G+R+B). In QGIS, thresholding (≥0.02) defined green vegetation. Zonal Statistics was used to extract green canopy cover (%) per plot. GY (13% moisture) was converted to kg/ha (Gonçalves et al., 2025). ANOVA and Tukey tests identified differences; Pearson correlation assessed GCC-yield relationships. All analyses were performed in GENES. Significant differences among hybrids (p < 0.05) were observed at 19, 98, 112, and 119 DAP. At 19 DAP (V2–V3), early-stage differences reflected genotypic variation in seedling vigor, which is fundamental for biomass accumulation and initial competition with weeds. At 98 DAP (R3–R4), corresponding to the grain formation phase, differences among hybrids in green canopy coverage became more evident. Hybrids LG 6036 (H6) and 30F35R (H7) maintained higher GCC values, suggesting greater leaf longevity and photosynthetic capacity. In contrast, interpopulation UENF hybrids (especially H3 and H4) showed reduced green cover, associated with faster onset of senescence. At 112 and 119 DAP (R4–R6), these differences were accentuated. As shown in Tukey test, H6 and H7 reached the highest GCC values (~50%), indicating superior stay-green behavior, while H3 and H4 presented values below 15%, characterizing rapid senescence. This phenotypic divergence in canopy maintenance reflects physiological differences in resource allocation and stress resilience. The strong positive phenotypic correlations between GCC and grain yield at 112 and 119 DAP (r = 0.88 and 0.96, respectively) confirm that prolonged canopy greenness enhances sink filling and yield. These results demonstrates that extended photosynthetic duration during grain filling contributes significantly to productivity. Commercial hybrids maintained greener canopies longer, which contributes to prolonged photosynthesis and improved yield potential under subtropical conditions. Additionally, your thesis evidences that commercial hybrids with longer reproductive phases preserved canopy integrity longer than UENF hybrids, which have extended vegetative and shorter reproductive stages. This cycle mismatch contributed to early senescence and reduced grain yield in UENF materials. Therefore, using VARI for monitoring GCC over time enables effective identification of stay-green genotypes, especially in climates prone to water stress and thermal fluctuations. Integrating such phenotyping tools into breeding programs supports the selection of hybrids with enhanced adaptability and yield stability under subtropical conditions. VARI-derived green canopy cover successfully differentiated maize hybrids with stay-green traits. Commercial hybrids such as LG 6036 and 30F35R maintained higher GCC at late stages and produced greater yields. The VARI index, applied via UAV-RGB imagery, proved to be a reliable tool for high-throughput phenotyping in breeding programs.