Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Micheal D. K. Owen


Woolly cupgrass survived nicosulfuron applications by initiating new tillers and because late season germination usually resulted in unsatisfactorily control. Research was initiated to determine the mechanism(s) of woolly cupgrass surviving nicosulfuron and the effects of tillage and preemergence herbicides on woolly cupgrass population dynamics. Woolly cupgrass demonstrated a strong tillering ability. When the first tiller emerged 10 to 12 d after planting, the woolly cupgrass seedling had already initiated 9 tiller buds. The vascular connection between the main stem and tillers was examined and no physical barrier was found that would prevent herbicide translocation. 14C-labled nicosulfuron was detected in the tiller buds 24 h after treatment. Woolly cupgrass tiller emergence following nicosulfuron application was not due to the herbicide restricting the tiller buds. Woolly cupgrass seed reserve was used up before the first tiller emerged, thus the seed reserve did not support the tiller growth. Tiller emergence was affected by apical dominance, physical constraint imposed by the leaf sheath, and nicosulfuron rates. Apical dominance imposed by the main stem limited nicosulfuron translocation to tillers, rendering tillers less susceptible to the herbicide. The leaf sheath provided a strong physical constraint restricting tiller growth, and with the negative effect of nicosulfuron, tillers could not emerge and eventually died with the mother plant. The recommended nicosulfuron rate, 35 g ai ha-1, inhibited the growth of the main stem, yet did not inhibit tiller growth, and prolific tillering occurred. Conventional tillage significantly decreased woolly cupgrass populations. Germination depth of woolly cupgrass in conventional tillage was significantly deeper than in no-tillage. However, the results varied at different locations and years. There were differences in populations among herbicide treatments. Germination depth increased for later germination events, however, differences among herbicides were not significant. When seed production was eliminated, the woolly cupgrass seedbank was depleted in three years.



Digital Repository @ Iowa State University,

Copyright Owner

Ming-Chung Liu



Proquest ID


File Format


File Size

107 pages