Composition of weed flora in spring cereals in Finland - a fourth survey

H Jalli,J Salonen,T Hyvönen

doi:10.2137/145960611797471534

Abstract

The weed flora in conventionally and organically grown spring cereals was investigated in southern and central Finland during 20072009. The survey was conducted in 16 regions, 283 farms and 595 fields (72 organically cropped and 523 conventionally cropped fields, of which 503 were treated with herbicides). The occurrence of weeds was assessed in late Julyearly August. Altogether 148 weed species were identified, of which 128 were broad-leaved and 20 grass species. In organically cropped fields, the average species number per field was 21 and the most frequent species were Chenopodium album 96%, Stellaria media 94%, Viola arvensis 94% and Elymus repens 89%. In conventionally cropped fields, the average species number was 12 and the most frequent weed species were Viola arvensis 83%, Stellaria media 65%, Galeopsis spp. 59% and Galium spurium 59%. The average density of weeds was 160 m-2 (median = 112) in sprayed conventional fields and 519 m-2 (468) in organic fields. The average air-dry biomass of weeds was 167 kg ha-1 (median = 82) and 775 kg ha-1 (563), respectively. Elymus repens, the most frequent and abundant grass species, produced the highest proportion (about 30%) of the total weed biomass in both cropping systems. The frequency of Galium spurium in conventional cropping and Fumaria officinalis in organic cropping had increased substantially since the previous survey in 19971999. The average size of the weed seedbank in the 5 cm surface layer was about 1 700 seeds m-2, the most predominant seeds being of C. album. Although the weed flora in Finnish spring cereal fields consists of numerous species, only a fraction of them severely threaten crop production in terms of their frequency and abundance. Weeds in conventional cropping were effectively controlled with available herbicides whereas weed management in organic cropping calls for urgent measures such as direct mechanical weed control in crop stands, which was not practised at all in survey fields.;

Highlights

Three extensive surveys of weeds in spring cereal fields have been carried out in Finland since the1960s, the first in 1961–1964 (Mukula et al 1969), the second in 1982–1984 (Erviö and Salonen 1987)and the third in 1997–1999 (Salonen et al 2001a).In addition to conventionally cropped fields, organically cropped fields were included in the survey protocol in the 1990s.Similar comprehensive weed surveys have been conducted earlier in many countries, but new surveys and follow-up monitoring have been realized to a lesser extent
We report the results of the fourth extensive weed survey of Finnish spring cereals, conducted in 2007–2009
We expected that continuous changes in cropping practices affect the species composition of the weed flora and the level of weed infestation, as discussed for instance by Andreasen and Streibig (2010)

Summary

Introduction

1960s, the first in 1961–1964 (Mukula et al 1969), the second in 1982–1984 (Erviö and Salonen 1987). In Finland, a small-scale survey of weeds in organically cropped spring cereals in coastal regions was carried out in the early. Since the previous extensive weed survey in Finland (Salonen et al 2001a), which was conducted in 1997–1999, agri-environment policy has influenced the preconditions for cereal production. We report the results of the fourth extensive weed survey of Finnish spring cereals, conducted in 2007–2009. We expected that continuous changes in cropping practices affect the species composition of the weed flora and the level of weed infestation, as discussed for instance by Andreasen and Streibig (2010). Since factors like the use of herbicides (Hyvönen and Salonen 2003), crop rotations (Sjursen 2001) and changes in tillage practices (Yenish et al 1992). Weed shift is of agronomic interest primarily as regards the most abundant weeds species

Material and methods

Findings

Discussion