Understanding maize-weed competition: resource competition, light quality and the whole plant

Although weed research in maize has broadened from an emphasis on herbicide technology to include studies of weed-maize competition, many studies only consider competition descriptively (e.g. defining the critical period for weed control). Furthermore, studies of the mechanisms of weed competition in maize have considered only competition for resources such as soil moisture, nutrients and light. Physiological ecologists have recently recognized the significance of early detection of neighbouring plants through the far-red/red (FR/R) signal as an important mechanism affecting plant-plant interactions, in this review, we have indicated the importance of integrating the concept of the mechanism of early detection of neighbours with the resource-limiting approach in reassessing weed competition in maize during the critical time for weed control. Hypothetical integration of early detection of neighbours into the existing concepts of critical time for weed control and weed thresholds led us to view maize-weed competition as a series of complex processes, which is triggered by the FR/R signal and followed by the development of shade avoidance characteristics accompanied by a reduction in the plant's ability to absorb nutrients and water, and to photosynthesize. However, due to lack of research on effects of weeds on light quality impinging corn plants as well as corn response to an increase in FR light during critical time for weed control, our conclusions remain to be speculative. We believe that incorporation of early detection of neighbours through the FR/R ratio as a primary signal during the critical period for weed control would open a new approach for future studies on weed competition in maize. We recognize that resource limitation occurs in a maize-weed association, however, this may be more of an effect rather than a cause of competition. (C) 2001 Elsevier Science B.V. All rights reserved.