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
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)
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).