Tolerance and velvetleaf (Abutilon theophrasti) suppressive ability of two old and two modern corn (Zea mays) hybrids

Improved crop tolerance and weed suppressive ability are tactics that may reduce the negative effect of weeds on crop yield. Irrigated field experiments were conducted to compare leaf area index (LAI), intercepted photosynthetic photon flux (PPF), and relative tolerance and velvetleaf suppressive ability among two old (circa 1940) and two modern corn hybrids. Each hybrid was grown in monoculture and in mixture with velvetleaf at 1, 4, 16, and 40 plants m^-1 row. Plants were periodically harvested in monoculture plots to obtain estimates of corn LAI, and PPF interception was measured. Variation in hybrid tolerance to velvetleaf competition for light was evaluated by comparing among hybrids the coefficients of a regression of corn yield loss on velvetleaf density. Velvetleaf seed capsule production in the presence of each hybrid was compared to evaluate variation in velvetleaf suppressive ability among hybrids. Maximum corn yield loss was 32% lower for the two old hybrids, and velvetleaf capsule production was reduced by 62% at low velvetleaf densities in 1995 compared to the modern hybrids. In 1996, yield loss of the modern hybrid 3394 was 74% lower than that of the other three hybrids at low velvetleaf densities, whereas maximum yield loss of the old hybrid 336 was 44% lower at high densities. Velvetleaf capsule production did not vary among hybrids at any velvetleaf density in 1996. Hybrids with greater tolerance and velvetleaf suppressive ability also had greater LAI and PPF interception, suggesting optimized corn LAI and PPF interception may be useful in an integrated weed management program.