Comparison of simple yield loss models
At the time of establishment of the Working Group, research related to crop-weed interactions focused on the construction of robust damage relationships to support rational decision-making on the use of herbicides. Multi-location trials were laid out by the Working Group members (from Finland to Spain and from Italy to the UK and Canada) to evaluate the yield-loss weed density model of Cousens (1985) and the relative leaf area model of Kropff & Spitters (1991). The evaluation confirmed the good descriptive ability of both models (Lotz et al., 1996). At the same time, predictive ability of both models was found to be poor and suggestions for improvement were made.

References

Cousens, R., 1985. An empirical model relating crop yield to weed and crop density and a statistical comparison with other models. J. Agric. Sci. 105, 513-521.

Kropff, M.J. & C.J.T. Spitters, 1991. A simple model of crop loss by weed competition from early observations on relative leaf area of the weeds. Weed Res. 31, 97-105

Lotz, L.A.P. et. al., 1996. Prediction of the competitive effects of weeds on crop yields based on the relative leaf area of weeds. Weed Res. 36, 93-101.

Cultural control measures
In the last decade, interest in weed management strategies that are less dependent on herbicides has increased. As a result, agronomic measures to manipulate crop-weed interactions, like competitive cultivars, crop spatial arrangement and timing, level and placement of fertilizers, have opened new scope for research in the area of crop-weed interactions. The same holds for the introduction of intercropping practices to suppress weeds.

More attention for population dynamics
In systems that aim at a reduced reliance on herbicides, the time horizon of interest is extended and main emphasis is given to long-term management of weed populations. In this situation, the effect of the crop on the weed, particularly on weed seed production, becomes increasingly important. Consequently, research on crop-weed interactions merges with weed population dynamics. In line with this, decision support models are being developed that model the consequences of cropping systems on the population dynamics of weeds.