Weed control thresholds are often presented as a means to reduce unnecessary control measures, thereby increasing the effectiveness of weed management. While the threshold is a useful tool for cost-effective application of control on a single-year base, its role over the longer term is more complicated. It is shown that long-term apphcation of thresholds results in a control frequency that is independent of threshold level, and in aperiodic dynamics of the weed population which may cause uncertainty about what control frequency and hence what costs of control are expected over a given period. We conclude that the economic underpinning of the threshold concept is deceptive and does not provide a base for rational use of weed control in the long term.
Wallinga, J., & van Oijen, M. (1997). Level of threshold weed density does not affect the long-term frequency of weed control. Crop Protection, 16(3), 273-278. https://doi.org/10.1016/S0261-2194(96)00091-9