Mechanisms of Corn Tolerance and Velvetleaf Suppressive Ability

Crops that better tolerate weed competition or preempt resources from weeds may reduce dependence on herbicides for weed control and benefit an integrated weed management program. Irrigated field experiments were conducted to identify morphological traits of corn (Zea mays L.) that enhance its tolerance and weed suppressive ability. Two old (circa 1940) and two modern corn hybrids were grown in mixture with five target densities of velvetleaf (Abutilon theophrasti Medik.) in two years. Corn height and leaf area index (LAI) were measured periodically throughout the growing season. Vertical leaf area distribution was measured at corn anthesis. Quantitative estimates of these traits were obtained for each experimental unit using linear and nonlinear regression analysis. Magnitude of the correlation between these trait estimates and corn yield reduction in mixture with velvetleaf or velvetleaf seed capsule production was used as an indicator of the importance of each trait to the enhancement of corn tolerance or velvetleaf suppressive ability. Canopy traits having highest correlation with corn relative yield in 1995 were maximum LAI (r= −0.38) and crop density (r = −0.24). Those with highest correlation in 1996 were crop density (r = -0.36), degree days accumulated between emergence and 50% maximum height (r = 0.34) and LAI (r = 0.19), and vertical leaf area distribution (0.49). Corn canopy traits were not correlated with velvetleaf seed production in 1995. However, vertical leaf area distribution (r = 0.60), maximum LAI (r = −0.32), and corn density (r = −0.26) were correlated with velvetleaf seed production in 1996. Results suggest that increasing maximum corn LAI, rate of canopy closure, or height at which leaf area occurs in the canopy can improve corn tolerance and velvetleaf suppressive ability. These traits can be modified by varying cultural practices such as row spacing and population density, or through breeding. Contribution of the Univ. of Nebraska Agric. Res. Div. Journal Series no. 12034.