Weed infestation in Weed infestation in

multimulti--year cultivation of year cultivation of

glyphosateglyphosate--resistant maizeresistant maize

Roundup Ready Maize SymposiumRoundup Ready Maize SymposiumBrussels, 22 Brussels, 22 --24 March 201024 March 2010

Dr Arnd VerschweleDr Arnd Verschwele

Julius KühnJulius Kühn--Institut, GermanyInstitut, Germany

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

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)

Trial sites

Gerbitz

Vesbeck

Werne

• 6 years of maize (2003-2008)

• 3 sites in Germany

• 8 herbicide treatments

Site Gerbitz Vesbeck W erne

Mean temperature (°C) 8.9 8.7 9.6

Precipitation (mm) 483 699 749

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 x4 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)

Experimental design

5 6 7 8

1 2 3 41 2 3 4

a

b

c

d

18 m

3 m

• 4 subplots systematically distributed within the plot

• Weed flora:estimated within the subplots

• Weed seed bank:soil sampled around the subplots

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

Weed seed bank (N)

Mean values of all treatments

Seed bank ratio (2003-2009)

b

aa

a

a a a

a

a

a

a

a

Species richness (S)

Mean values of all treatments

Species richness ratio (2003-2009)

b

a

a

a

a

a

ab

a

a

a

a a

a

ab

Shannon‘s diversity index (H)

Mean values of all treatments

Shannon‘s diversity ratio (2003-2009)

a

a

b

a

a

a a

aab

a

aa

Seed bank (N) Species richness (S)

Annual effects (all subplots)

Ratio of 1 indicates no difference compared to the previous year, n=269

Shannon‘s diversity (H) Dominance (D)

Gerbitz: Vesbeck: Werne:

Relative abundance (log plot)

3+3 Roundup Ready:

Site effects: Chenopodium album

Site effects: Solanum nigrum

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 - - -Solanum nigrum 2 - - -

Trifolium repens 2 - - -

Urtica urens 1 ++ + 0

Viola arvensis 2 - - 0

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).