Multiyear field data from Spain were used to model seedling emergence for three bedstraw species (Galium) that can coexist in winter cereal fields. The relationships between cumulative emergence and both growing degree days (GDD) and hydrothermal time (HTT) in soil were analyzed as sigmoid growth functions (Weibull). Iterations of base temperature and base water potential were used to optimize the HTT scale. All species were well described with Weibull functions. Both GDD and HTT models provided good descriptions of catchweed bedstraw emergence, as its seedlings have less dependence on soil water potential than false cleavers and threehorn bedstraw, which were described best with HTT. The HTT model for catchweed bedstraw was validated successfully with independent data from the United Kingdom. The models may be useful for predicting bedstraw emergence in semiarid Mediterranean regions and elsewhere.

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The emergence of three artificial cohorts of Galium aparine, G. spurium and G. tricornutum with different accessions was studied over two years under the climatic conditions of north-eastern Spain. Seeds were sown in November (first cohort), January (second cohort) and February (third cohort). Higher and lower emergence percentages were obtained in the first and third cohorts, when fresher winter and dry spring occurred. However, this tendency changed when the spring was wet and emergence of third cohorts was more than that of the first. Results suggest that low temperatures in winter break the dormancy of these species, that soil moisture promotes the germination and emergence of these weeds and that emergence is highly influenced by dormancy levels during winter and spring. Lack of rain does not allow spring germination, hence, application of herbicides to control spring cohorts is not necessary.

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Royo‐Esnal A, Torra J, Conesa JA & Recasens J (2012). Emergence and early growth of Galium aparine and Galium spurium. Weed Research. 52, 458–466. Summary With the aim of improving the control of Galium aparine and G. spurium, field experiments were conducted in a Mediterranean winter cereal field. Emergence and early growth (in number of whorls) of six populations of these weeds were examined. Populations were sown in November 2005 and 2006 with four randomised complete blocks in north‐eastern Spain. Emergence was determined by counting and marking newly emerged seedlings weekly for 3 months and vegetative growth was evaluated for each marked seedling group using the expanded BBCH (Biologische Bundesanstalt Bundessortenamt and Chemical industry) scale. Linear regressions were successfully fitted to the growth, using degree days and hydrothermal time as factors. Growth pattern differed between both years, but not between both Galium species, when fitted to growing day degrees (GDD), but these differences disappeared when fitted to hydrothermal time (HTT). Despite disparity in the emergence pattern among populations, new whorl production followed similar patterns for each Galium species, which allowed development of a common model. Maternal factors may have affected emergence, but populations did not show differences in whorl development. This growth model is a new tool that may be used to improve the timing of weed control strategies for Galium species in winter cereal fields under a Mediterranean climate.