Summary The extended BBCH scale is a system for a uniform coding of phenologicaliy similar growth stages of all mono‐ and dicotyledonous plant species, based on the well known cereal code of Zadoks et al. (1974). The BBCH key is it decimal system, with 10 principal growth stages and up to 10 secondary ones, starting with seed germination, sprouting of perennials, progressing through leaf production and extension growth to flowering and senescence. Therefore, it can also be a suitable tool to define the growth stages of different weed species. To encourage further use of the BBCH scale in weed research, definitions of the codes have been more closely adapted to weeds. Possible problems are discussed and guidelines for correct use are given.

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Summary A prerequisite for a precise estimate of the abundance of weed seeds in sou is prior knowledge of sampling variability, Based on an analysis of EWRS working group trials, it is shown that the sampling variance (s2) of seed counts increases with the sampling mean (S2) and can be predicted with the logarithmic form of Taylor's power law: log10(sz)=a+b log10(x̄). This relationship is constant over time for means greater than 0.1 seeds per core within each of the five different sites studied (temporal variability) but differs slightly among sites (geographical variability). An attempt is made to use a general s2 : x̄ relationship to predict the number of samples as a function of precision and density.