Weed control

PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 37 JANUARY 2009 ISSN 2070-3740

Estimation of Critical Period for Weed Control in Corn in Iran
Sohrab Mahmoodi1 and AliRahimi 2
CPWC it is possible to make decisions on the need for and timing of weed control, and to control weeds only when efficient weed control is required. The CPWC could be used also to enhance theefficiency of other methods of weed management, including cultivation and flaming. Also reducing the number of herbicide treatments as a result of better timing and efficiency may reduce potentialenvironmental contamination and the selection pressure for herbicideresistant weeds [7]. The CPWC is the time period in the crop growth cycle during which weeds must be controlled to preventunacceptable yield loss [4]. It has been defined as the time interval between the maximum weed-infested period, or the length of time that weeds which emerge with the crop can remain uncontrolled before theybegin to compete with the crop and cause yield loss, and the minimum weed-free period, or the length of time that the crop must be free of weeds after emergence [12]. Thus, it is the minimum period oftime during which the crop must be free of weeds to prevent crop yield loss. Knezevic et al.[10] described CPWC as a "window" in the crop growth cycle during which weeds must be controlled to preventunacceptable yield losses. The length of the CPWC may vary depending on the acceptable yield loss [7]. This concept is closely related to the use of weed thresholds, defined by Dawson [2] as the lengthof time that a crop can tolerate weed competition before yield loss exceeds the cost of control. The CPWC is determined by calculating the time interval between two components of weed interference.These are (1) the critical weed interference period or the maximum length of time during which weeds emerging soon after crop planting can coexist with the crop without causing unacceptable yield...