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Weed infestation in multi-year cultivation of glyphosate resistant maize

Weed infestation in multi-year cultivation of glyphosate resistant maize

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  • 1. Weed infestation in multi- multi-year cultivation of glyphosate- glyphosate-resistant maize Dr Arnd Verschwele Julius Kühn-Institut, Germany Kühn- Roundup Ready Maize Symposium Brussels, 22 -24 March 2010
  • 2. Objectives Is there a glyphosate-induced weed shift? • ecology: loss of biodiversity? • agronomy: spread of tolerant or resistant species? Investigations and evaluations in terms of weed shift: • general: weed abundance, seed bank, diversity • specific: effects on individual species
  • 3. Analysis of weed diversity Indicators: • Species richness: (S) • Abundance per species (n) and total (N) • Dominance: (D) = nmax N-1 • Shannon’s index of diversity: (H) = (N ln N - ∑ n ln n) N-1 • Shannon’s index of evenness: (E) = H (ln S)-1 • Relative abundance (log plot)
  • 4. Trial sites • 6 years of maize (2003-2008) Vesbeck • 3 sites in Germany Werne Gerbitz • 8 herbicide treatments Site Gerbitz Vesbeck W erne Mean temperature (°C) 8.9 8.7 9.6 Precipitation (mm) 483 699 749
  • 5. Herbicide treatments No. Herbicides Year 03 04 05 06 07 08 1 Local standard (LOCSTD) x x x x x x 2 1.5 + 1.5 RR x x x x x x 3 2.0 + 2.0 RR x x x x x x 4 3.0 + 3.0 RR x x x x x x 5 3.0 RR* + 2.0 Acetochlor x x x x x x 6 2.0 + 2.0 RR x x x x 2.0 Lentagran + 0.5 Bromotril x x 7 2.0 + 2.0 RR x x x x 0.15 MaisTer x x 8 2.0 + 2.0 RR x x x x 1.0 Terano x x * RR=Roundup Ready (360 g L-1 glyphosate)
  • 6. Experimental design 5 6 7 8 1 2 3 4 d • 4 subplots systematically c distributed within the plot 3m • Weed flora: b estimated within the subplots • Weed seed bank: a soil sampled around the subplots 18 m
  • 7. Initial weed situation in 2003 Site Gerbitz Vesbeck Werne Seed bank (N m-2) 3810 28388 15633 Species richness (S soil) 8 19 17 Species richness (S field) 5 12 10 Shannon’s diversity (H) 1.10 1.77 2.03 Shannon’s evenness (E) 0.52 0.59 0.72 Predominant species CHEAL SOLNI VERSS AMARE POAAN STEME URTUR CAPBP SOLNI
  • 8. Weed seed bank (N) Mean values of all treatments
  • 9. Seed bank ratio (2003-2009) b a a a a a a a a a a a
  • 10. Species richness (S) Mean values of all treatments
  • 11. Species richness ratio (2003-2009) a a b a a ab ab a a a a a
  • 12. Shannon‘s diversity index (H) Mean values of all treatments
  • 13. Shannon‘s diversity ratio (2003-2009) a a a b a ab a a a a a a
  • 14. Annual effects (all subplots) Ratio of 1 indicates no difference compared to the previous year, n=269 Seed bank (N) Species richness (S) Shannon‘s diversity (H) Dominance (D)
  • 15. Relative abundance (log plot) 3+3 Roundup Ready: Gerbitz: Vesbeck: Werne:
  • 16. Site effects: Chenopodium album
  • 17. Site effects: Solanum nigrum
  • 18. Weed shift trends Weed species Sites 1.5+1.5 3+3 LOCSTD Amaranthus retroflexus 2 + + + Chenopodium album 3 + 0 0 Polygonum convolvulus 1 - - - Solanum nigrum 2 - - - Trifolium repens 2 - - - Urtica urens 1 ++ + 0 Viola arvensis 2 - - 0
  • 19. Summary • The weed diversity in maize was rather high: - 94 weed species overall (15 species just once) - 37 species in 2003, 53 species in 2009 (seed bank) • Treatment effects were less significant than those by site and year (maize monoculture). • Roundup Ready had no negative effect on weed diversity (compared to the local standard). • So far, resistant biotypes were not found. • High dosage was required for a safe control of some weed species (e.g. Urtica urens. Chenopodium album).