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     

The influence of interspecific interference on the seed production of Stellaria media and Hordeum vulgare (volunteer barley)

The effects of the density and proportion of both volunteer barley ( Hordeum vulgare L.) and Stellaria media (L.) Vill. (common chickweed) on the seed yield of both species was investigated in linseed ( Linum usitatissimum L.) and autumn-sown field bean ( Vicia faba L.). A model was created to estimate these effects. It was a combination of two models. The first was a simple linear model relating weed seed number m² to weed dry weight m². The second was an inverse linear model relating weed dry weight per plant to weed density. A very good relationship existed between barley dry weight and number of seeds m² and between S. media dry weight and number of seed capsules m². This relationship was relatively consistent between experiments. The inverse linear model provided a good estimation of the relationship between weed density and weed dry weight per plant for both barley and S. media . Model variables, however, differed between experiments. Using the combined model it was estimated that, in the absence of other weed species and at a density of 800 plants m², S. media would produce between 4000 and 48 000 seeds m², whereas volunteer barley, at a density of 400 plants m², would produce between 2000 and 8000 seeds m². The presence of barley always reduced S. media seed yield and a barley population of 100 plants m² could reduce S. media seed yield by up to 79%. The presence of S. media reduced barley seed yield in only one of three experiments, in which a S. media density of 800 plants m² reduced barley seed yield by up to 68%. It was concluded that interspecific weed competition should not be ignored as a factor in models of weed population dynamics     

Predicting yield loss due to interference from two weed species using early observations of relative weed leaf area

Experiments were conducted on linseed ( Linum usiãissimum L.) and autumn-sown field bean ( Vicia faha L.) to test how well the relative leaf area-based yield loss prediction model of Kropff & Spitters could estimate yield loss due to interference from Stellaria media L. (common chick-weed) or barley ( Hordeum vulgare L.) alone or a combination of both S. media and barley . Damage coefficients were calculated for all comparisons. Generally, the model provided a better estimate of yield loss due to interference from barley than from S. media because of both the variability in crop yield response stemming from S. media's plasticity and the generally minor crop yield response to S. media interference. The addition to the model of a parameter accounting for asymptotic yield loss was, generally, not warranted for either S. media or barley in the single-weed species data sets. When both S. media and barley were present as weed species in the crop, the model that fitted the data best for six out of 10 data sets was the one in which a separate damage coefficient was included for both species. There was no evidence that the presence of S. media influenced damage coefficient values for barley. However, in the presence of barley a parameter accounting for asymptotic yield loss was warranted for S. media in the two-weed species model. The combination of the addition of this parameter and the presence or barley affected the values of the damage coefficients for S. media in the two-weed species compared with the single-weed species models. Consequently, it was shown for these two weed species that two-weed species yield loss prediction models parameterized using data from single-weed species experiments generally resulted in different estimates of yield loss in comparison with models parameterized using data from two-weed species experiments.     

Weed biology serves practical weed management

Weed science is an applied science that serves practical weed management. Traditionally, effective weed management has been dependent upon farmers gaining knowledge of the characteristics of the weeds they were managing. The advent of herbicides has not made this knowledge-based approach redundant and problems, including herbicide resistant weeds, have made weed biology studies necessary even in the herbicide era. Weed populations continue to evolve and weed problems persist, sustaining a requirement for effective management strategies. In this paper, we exhibit several approaches to linking weed biology studies to practical weed management. These approaches demonstrate both the value of and synergy between an in-depth knowledge of weed biology and weed management practices to provide practical solutions in the field.