Changes in the abundance of weeds in spring cereal fields in Finland

Abstract

SummaryThe data of two weed surveys of spring cereals (conducted in 1982–84 and 1997–99) in Finland were applied to study changes in the total abundance (the number of individuals and dry weight) of the weed community as well as in the abundance and frequency of occurrence of single species. The estimated overall mean for the differences in total dry weight was 31.1 kg ha−1 and the differences in the total number of individuals was 46.6 individuals m−2 with higher numbers in the 1990s. Most of the overall variability in dry weight (63%) and in number of individuals (57%) was attributable to variability between fields within the same farm. None of the environmental variables could explain the variability in the difference in dry weight, or in the number of individuals between decades. Descriptive analysis of the single species data revealed a higher abundance and frequency of occurrence of most species in the 1990s than in the 1980s. No statistically significant differences were detected in the number of individuals of species tolerant of sulfonylureas (pooled data on Galium spurium and Viola arvensis) between decades. The results are discussed in relation to changes in the use of herbicides.