Weed infestation in multi-year cultivation of glyphosate resistant maize

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).