ADDITIVE INFESTATION MODEL (AIM) ANALYSIS FOR THE STUDY OF 2-WEED SPECIES INTERFERENCE

A graphical method of analysis designed to study the efficacy of herbi cide mixtures, the additive dose model, was adapted for use in analysi ng the effect of two-weed species interference on crop yield. It is po ssible to categorize two-weed species interference as synergistic or a ntagonistic with regard to the effect on crop yield. It is also possib le to quantify the degree to which the effect of species mixture devia tes from additivity. Within the analysis, different forms of regressio n models may be used to estimate interference from one species or anot her, 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 fiel d experiments in which the influence of Stellaria media (L.) Vill. and barley on linseed yield was estimated. Further work is required to de velop confidence intervals for the method, so that departures from add itivity can be examined statistically.