A Verschwele

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Weed infestation in multi-year cultivation of glyphosate resistant maize

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A Verschwele

  1. 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. 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. 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. 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. 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. 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. 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. 8. Weed seed bank (N) Mean values of all treatments
  9. 9. Seed bank ratio (2003-2009) b a a a a a a a a a a a
  10. 10. Species richness (S) Mean values of all treatments
  11. 11. Species richness ratio (2003-2009) a a b a a ab ab a a a a a
  12. 12. Shannon‘s diversity index (H) Mean values of all treatments
  13. 13. Shannon‘s diversity ratio (2003-2009) a a a b a ab a a a a a a
  14. 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. 15. Relative abundance (log plot) 3+3 Roundup Ready: Gerbitz: Vesbeck: Werne:
  16. 16. Site effects: Chenopodium album
  17. 17. Site effects: Solanum nigrum
  18. 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. 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).
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