MODELING WEED COMPETITION AND YIELD LOSSES TO STUDY THE EFFECT OF OMISSION OF HERBICIDES IN WINTER-WHEAT

Various experiments were carried out to study the effect of herbicide treatment on the yield of winter wheat. Omission of herbicide application caused a significantly lower crop yield only when the densities of certain weed species were extremely high in spring. A dynamic model simulating the competition for light and water between broad-leaved weeds and winter wheat was used to analyse these experimental results. The aim of this analysis was to assess the observed small effects of annual broad-leaved weeds on yield of winter wheat in terms of the relative emergence time and physiological and morphological characteristics of the weeds. Like the experiments, the simulations indicated that in the Netherlands weeds emerging in spring hardly affect crop yield. Weeds emerging in autumn, however, may reduce crop yield considerably if they grow as tall as winter wheat (20 % loss at density of 100 plants per m2). The results are discussed in relation to characteristics of crop rotation systems that include root and tuber crops.