Morphology and yield response to weed pressure by corn hybrids differing in canopy architecture

Recently, corn (Zea mays L.) hybrids accumulating more leaf area above the ear, maturing earlier, yielding better in narrower row spacings and tolerat ing higher population densities than conventional hybrids have been develop ed. However, no research has been conducted to assess their ability to comp ete with weeds. The objective of this study was to quantify morphological a nd grain yield responses of hybrids with differing canopy architectures to the presence and absence of weeds. Field experiments were conducted in 1996 , 1997, and 1998 at Ste. Anne de Bellevue, Quebec and in 1996 at Ottawa, On tario. Three hybrids, leafy reduced-stature (LRS), late maturing big leaf ( LMBL), and conventional Pioneer 3979 (P3979), were evaluated at two populat ion densities (normal and high), row spacings (38 and 76 cm) and weed press ure levels (weed-free and weedy). Weed pressure reduced the plant height of LRS less (only 4 cm) than the tall hybrids (average reduction of 26 cm). T he overall grain yield of the LMBL hybrid was much greater (12.7 mg ha(-1)) than the LRS (9.6 mg ha(-1)) and P3979 (11.0 mg ha(-1)) hybrids in the abs ence, but not in the presence (LRS, 6.5; LMBL, 6.7; and P3979, 6.8 mg ha(-1 )), of weeds. The yield of early-maturing LRS and P3979 (especially LRS) hy brids, were least affected by weed pressure, suggesting better tolerance of , and competition with, weeds. However, further research with more LRS hybr ids is needed, as is the development of better yielding LRS hybrids, before they can be recommended over conventional hybrids. (C) 2001 Elsevier Scien ce B.V. All rights reserved.