Additive infestation model (AIM) analysis for the study of two-weed species interference

A graphical method of analysis designed to study the efficacy of herbicide mixtures, the additive dose model, was adapted for use in analysing the effect of two-weed species interference on crop yield. It is possible to categorize two-weed species interference as synergistic or antagonistic with regard to the effect on crop yield. It is also possible to quantify the degree to which the effect of species mixture deviates from additivity. Within the analysis, different forms of regression models may be used to estimate interference from one species or another, or for species in combination, provided that the models used are all special cases of the same basic model. This allows for flexibility in summarizing data. The method was demonstrated using data from field experiments in which the influence of Stellaria media (L.) Vill. and barley on linseed yield was estimated. Further work is required to develop confidence intervals for the method, so that departures from additivity can be examined statistically.