Agronomy and Horticulture Department


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor John Lindquist. Lincoln, Nebraska: December, 2012

Copyright (c) 2012 Rodrigo Werle


Winter annual weeds are becoming more common in many row crop fields in the midwestern USA. The impact of winter annual weeds in cropping systems is often overlooked because these weeds complete their lifecycle near the time of crop sowing. However, delayed soil warming, competition for nutrients during initial establishment of the main crop, difficult planting operations, and yield loss are some of the problems caused by dense mats of winter annual weeds. Moreover, some of these weeds have been reported as alternative hosts for pests such as the soybean cyst nematode (Heterodera glycines, SCN), considered the most important soybean pathogen in the USA. Research looking at the effect of time of herbicide application on SCN development on weed hosts has not been reported. Thus, our first objective was to evaluate how the development of SCN on henbit roots was affected by time of herbicide application and herbicide mode of action. The results of this research indicated that early management of henbit plants can significantly reduce SCN reproduction potential in the absence of its main host, soybean. In order to better manage weeds, it is important to know when they will emerge, since weeds are easily controlled during early stages of growth. The emergence pattern of winter annual weeds common to the midwest region of the United States has not been reported. Therefore, our second objective was to understand and predict emergence of winter annual weed species using models based on the accumulation of modified thermal/hydrothermal time. The results of this research indicated that soil temperature was the main factor driving winter annual weed emergence. According to our findings, the majority of the winter annual weeds will emerge by late-fall in Nebraska, indicating that, as long as environmental conditions are adequate for herbicide application or mechanical cultivation, this would be the ideal time to manage these weeds. These results may help farmers to better manage winter annual weeds.

Adviser: John L. Lindquist