Spatial distribution of annual grass weed populations in winter cereals

The spatial distribution of 12 annual weed species in 52 winter cereal fields was studied by applying frequency distribution and dispersion indices. Avena sterilis and Lolium rigidum were clearly the dominant species, infesting the 38% of the fields. The dispersion indices, viz. variance to media ratio, David and Moore's index, and k of the negative binomial revealed that the studied weed species followed an aggregated or contagious distribution pattern. In 54 of the 68 cases (specie-site) and in 10 of the 12 fields with multiple infestation studied, the weed populations were well represented by fitting the negative binomial distribution to frequency distribution of weed counts. Estimated values of parameter k showed a great variability amongst fields and were, in most cases, small indicating a high degree of patchiness. There was no stable or common k(c) value across field sites for all the weed species populations. This makes management decisions on weed control less easy in these fields. (C) 2003 Elsevier Science Ltd. All rights reserved.