'Stay-green’ (Sgr) maize cultivars have been selected to maintain a high green leaf area during the post silking development phase. Consequently they sustain higher photosynthetic activity than other cultivars at a time of high crop demand (Hay and Porter, 2006). This is critical because the largest proportion of dry matter partitioned to the grain is accumulated after silking (Muchow et al., 1990). Maintenance of green leaf area may also reduce the total nitrogen demand for crops and thus reduce the amount of inorganic fertilizer required.