EMERGENCE AND SURVIVAL OF HORSEWEED (CONYZA CANADENSIS)

Authors: Buhler, Douglas - Doug; OWEN, MICHEAL - IOWA STATE UNIVERSITY

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soil erosion continues to be a problem in many regions of the United States. No-tillage crop production systems are very effective in reducing soil erosion, but adoption of these systems by producers has been slow. Weed control is considered a major reason for the slow adoption. Weeds not usually considered a problem in fields that are tilled each year can rapidly become problems under no-tillage conditions, increasing potential crop losses due to weeds. Many of these weeds do well in no-tillage fields because they need an undisturbed habitat to complete their life cycle. Horseweed is a good example of this type of weed. It can invade no-tillage fields very rapidly because it occurs commonly in much of the eastern and central United States in field edges and roadsides, produces many seeds that can be moved with the wind, and is tolerant to many herbicides. Little is known about the winter survival and spring emergence of horseweed. The objective of our research was to evaluate the winter survival and spring emergence of horseweed in no-tillage cropping systems. We found that most of the horseweed emerged in the fall at both Rosemount, MN and Ames, IA. Winter survival of fall-emerged seedlings ranged from 59 to 91%. Horseweed also emerged in the spring at both locations. Spring emergence was greater at Rosemount than Ames and ranged from 5 to 32% of the total population. These findings are significant because it has often been assumed that horseweed emerges only in the fall. This has resulted in poor horseweed control and increased herbicide use in some fields. The results of this research will aid in the development of management practices to improve horseweed control and reduce herbicide use in no-tillage crop production systems.

Technical Abstract: Horseweed emergence and survival were evaluated in no-tillage soybean and corn at Rosemount, MN and Ames, IA from the fall of 1992 through the summer of 1995. Most of the horseweed emerged in the fall at both locations. Winter survival of fall-emerged seedlings ranged from 59 to 91%. Timing and extent of horseweed emergence in spring varied by year and location. Spring emergence ranged from 5 to 32% of total emergence with greater spring emergence at Rosemount than Ames. Emergence occurred as late as early June at Rosemount and late May at Ames. Results indicated that horseweed may emerge well into the growing season and spring emergence should be considered in weed management systems for no-tillage crop production.