How Much Do Weeds Impact Crop Yields?

Bob Hartzler
1997 Proceedings of the Integrated Crop Management Conference   unpublished
Introduction The primary purpose for controlling weeds in field crops is to prevent or reduce yield losses associated with competition between weeds and the crop. Competition occurs when plants seek the same resource (light, water, etc.) that is available in limited supplies. The interaction between crops and weeds is complicated and impacted by many factors, including characteristics of the weed species, weed populations, timing of weed emergence, characteristics ofthe crop variety/hybrid,
more » ... population and row spacing, and the environment. This complexity limits our ability to predict yield losses early in the growing season, therefore hindering the development of economic thresholds for weed. This paper will discuss two important factors influencing competition: 1) relative competitiveness of different weeds, and 2) the critical periods of competition. More information on this topic is available in ISU Extension bulletin IPM-35, Crop-Weed Interactions. Relative Competitiveness of Weeds Weed species vary widely in their competitiveness. A successful competitor must be efficient at capturing or using limited resources. Plant characteristics that impart these traits vary depending upon the resource being sought. Plant species that develop an extensive root system early in the growing season would be expected to compete effectively for nutrients and water. Leaf and plant height characteristics determine the competitiveness of a species for light. Giant ragweed would compete more effectively for light with soybeans than waterhemp because of its large foliar canopy. A system developed at the University ofNorth Carolina, and modified for Nebraska conditions by the University ofNebraska, provides a simple means of comparing the competitiveness of different weed species. The system is based on the competitive index (CI), which is a description of the relative competitiveness of a species. The CI is based on the relative competitiveness of a species in relation to sunflower. For example, the CI
doi:10.31274/icm-180809-557 fatcat:i6uwxeo52vgvngwscgjipvoioy