ABSTRACT
This book focuses on the effects of biotic stress on crop yield loss. In Chapter 12 we outlined a number of methods for quantifying the effects of weed interference on crop yield. In this context, it was important to use the term interference because experiments designed to show a relationship between crop yield and weed population density have not typically included methods of evaluating the cause of any observed yield reduction. In other words, although the yield reduction was likely caused by stress, the cause of that stress is unknown. It is possible that the loss was caused because the weed species under study acted as a trap crop for insects that subsequently caused stress through, for example, defoliation. Granted, most researchers interested in the effects of the weed would manage their experiment to eliminate such factors. However, the point is that if the stress was not quantified, it is impossible to say what actually caused the observed crop loss. Therefore, questions that need to be addressed include (1) how do weeds cause stress, and (2) how do we quantify the influence of this stress on crop yield?
