Experiments were conducted in pots and in the field to determine the influence of seed depth on seedling emergence pattern and control of Mexican sunflower with or without imazethapyr plus pendimethalin. Mexican sunflower seeds were placed at 0-, 2.5-, 5-, 7.5-, and 10-cm soil depths, and imazethapyr–pendimethalin mixture was applied PRE at 0, 0.05 + 0.65, 0.09 + 1.31, and 0.18 + 2.62 kg ae (+ ai)/ha. Mexican sunflower emergence was 57, 30, 14, 3, and 2% from 0-, 2.5-, 5-, 7.5-, and 10-cm seed depths, respectively. Seedling emergence started 2 to 3 d after planting and continued for 4 to 5 d. At 0- to 5-cm seed depths, 84 to 100% of total seedling emergence occurred within 3 d after the first seedling emerged, but emergence rate was less from 7.5- and 10-cm seed depths. Imazethapyr plus pendimethalin at 0.05 + 0.65 and 0.09 + 1.31 kg/ha had no effect on seedling emergence in Mexican sunflower, but subsequent growth was severely inhibited regardless of seed depth. The herbicide treatments were more injurious to Mexican sunflower seedlings that emerged from 5- to 10-cm depths than to those that emerged from 0 and 2.5 cm. Burying seeds 7.5 cm deep or more is a potential control measure for Mexican sunflower, and the deeper the emergence depth, the more susceptible the seedling is to imazethapyr plus pendimethalin.

Field experiments were conducted in 1992 to 1993 and in 1995 to 1996 in Ibadan, Nigeria, to assess the effect of velvetbean and herbicides on maize (corn) and cogongrass growth and to assess regrowth of the weed 1 yr after treatment. In 1992 and 1995 cover cropping with velvetbean and imazapyr and glyphosate application reduced cogongrass density as much as the handweeded control. The smothering effect of velvetbean was equivalent to that of glyphosate at 1.8 kg/ha but was less than imazapyr even at the lowest rate of 0.5 kg/ha. Addition of adjuvant did not improve the efficacy of either herbicide. Maize grain yield was higher in velvetbean plots than in fallow plots dominated by cogongrass. Velvetbean and herbicide effects on cogongrass 1 yr later (1993 and 1996) followed a similar trend as observed in the year of application. Annual weed density was highest in glyphosate plots, followed by imazapyr, and least in plots previously seeded to velvetbean. Maize grain yield was higher in herbicide plots (average yield of 3,170 and 1,920 kg/ha in 1993 and 1996, respectively) than in velvetbean plots (2,800 to 1,180 kg/ha in 1993 and 1996, respectively) and handweeded plots (2,890 and 723 kg/ha in 1993 and 1996, respectively). In 1996 the lowest maize yield was in handweeded plots without velvetbean, suggesting that weeding four times suppressed cogongrass density and biomass, but was not sufficient to minimize the subsequent competition from annual weeds. Uncontrolled cogongrass reduced maize yield to zero. These studies suggest that planting velvetbean for cogongrass control may be a better alternative for farmers without the resources to purchase herbicides.