ChristianAndreasen_Prague_Jun11

Prague, 14 June 2011Dias 1

Department of Agriculture and Ecology

Weed flora changes in responseto weed control over thelast 100 years

Associate Professor Christian AndreasenDepartment of Agriculture and EcologyCrop Science



Weed surveys in Denmark

1911-15 1940-45 1960-70 1987-89 2001-04

1910 1930 1950 1970 1990 2010

Crops: 2 2 19 9 11

Fields:64 50 466 357 407

l l l l l l l l l l l



Average number of species among 67 weed speciessurveyed in a single circle of 0.1 m2

0

1

2

3

4

5

6

7

8

Spring barley Spring rape Winter rye Winter wheat Grass leys

1967-701987-89



Changes of importance for the weed flora on the period 1987 to 2000

• Pesticide action plans• The amount of active ingredient has been reduced

50% and the treatment index has been reduced 1/4• New herbicides have been introduced • Set aside directives• Organic farming make up about 6% • The mean farm size has increased from 32.2 to 44.7ha • Change in use of cropping area



Average number of weed species

0

2

4

6

8

10

12

Springbarley

Spring rape Winter rye Winterwheat

Grass ley Peas Fodderbeets

Sugar beets Winterbarley

1967-701987-892001-04

Average number of species (±SD) recorded in a singleRaunkiær circle of 0.1 m2



Changes in frequency of Poa annuaFrequency %

0

10

20

30

40

50

60

70

80

90

Sugar beets Fodderbeets

S. barley S. rape Peas w. barley W. wheat W. rye Grass leys

1987-89

2001-04



Reasons for weed flora changes during the last 100 year

• Crop rotation • Fertilisation• Drainage• Herbicides• Seed cleaning• Mechanisation and changes in cultivation methods• Legislation



Cluster analysis of crops based on frequency of occurrence of all species in a Danish survey (2001-2004)A B

C D



Area of 10 crops as a fraction of the total arable area in Denmark

0

5

10

15

20

25

30

35

40

45

Winterrye

Springbarley

Winterbarley

Winterrape

Springrape

Maize Grassleys

Sugarbeets

Fodderbeets

Winterwheat

1967-701987-892001-04

Percentage of total

arable land

(From Andreasen & Stryhn, 2005)



Crop rotation

Is an important control methods to minimise the occurrence of weeds, which pose particularly

problems in specific crops

Apera spica-venti in cereals



New crops may create new weed problems!



Echinochlora sp. and Setaria viridis in maize

http://images.google.dk/imgres?imgurl=http://www.msuturfweeds.net/images/galleries/gr_fox/3.jpg&imgrefurl=http://www.msuturfweeds.net/details/_/green_foxtail_53/&h=375&w=500&sz=72&hl=da&start=12&um=1&tbnid=5eVFCqU7Vm5SuM:&tbnh=98&tbnw=130&prev=/images%3Fq%3DSetaria%2Bviridis%2B%26um%3D1%26hl%3Dda%26sa%3DG



Red fescue (Festuca rubra) Vulpia bromoides

From:florabase.calm.wa.gov.au



Nitrogen and fertilisation

Commercial Dung and slugde N-fixation From airFertilizer slurry manure

N fertiliser (kg/ha)

020406080

100120140160180200

1950 1960 1970 1975 1979

Average nitrogen fertilizer (kg/ha) used on arable land

(from Haas & Streibig, 1982)

(From: http://dmu.dk)



Nitrogen fertilisers favour nitrophilous species

Elytrigia repensPoa annuaChenopodium albumStellaria media

Enhance the shading ability of crops

Shade tolerant species

Poa annuaStellaria mediaViola arvense

Species able to elongate into more favourable light condition

Fallopia convolvulusGalium aparine

http://www.dkimages.com/discover/previews/739/45004476.JPG



Use of lime has tripled since 1950

Negative effect on calcifuge weed species:

Rumex acetosellaScleranthus annuusSpergula arvensis

Favour weed species like:

Veronica persicaAnagallis arvensisLamium purpureum



The effect of herbicides

0

50

100

150

200

Control 1,0l

% o

f unt

reat

ed

MCPA

Mechlorprop

Changes in the dry weight production of Galium aparine after spraying

with MCPA and Mecoprop

(From Petersen, 1960)

0.5 l /ha 1.0 l/ha 2.0 l/ha

Mecoprop

(Petersen, 1960)

http://images.google.dk/imgres?imgurl=http://popgen.unimaas.nl/~jlindsey/commanster/Plants/Flowers/SpFlowers/Galium.aparine.jpg&imgrefurl=http://popgen.unimaas.nl/~jlindsey/commanster/Plants/Flowers/spflowers2b.html&h=426&w=640&sz=55&hl=da&start=2&um=1&tbnid=GRcXcFS7MfpqJM:&tbnh=91&tbnw=137&prev=/images%3Fq%3DGalium%2Baparine%26um%3D1%26hl%3Dda

http://sauce.pntic.mec.es/ldepablo/images/Galium-aparine.jpg



70% effect level

90% effect levelU

ncer

tain

tyU

ncer

tain

ty

Dose response curve for a herbicide

Dose

Per

cent

effe

ct



Changes in frequency of Elytrigia repens

0

2

4

6

8

10

12

14

16

18

Sugar bee

tsFod

der bee

tsS. b

arley

S. rape

Peas

W. barl

eyW. w

heat

W. rye

Grass l

ey

1987-892001-04

Frequency %



Changes in frequency of Cirsium arvense

0

1

2

3

4

5

6

Sugar b

eets

Fodder

beets

S. barl

eyS. ra

pePea

sW. b

arley

W. whe

atW. ry

eW. ra

peGras

s ley

s1987-892001-04

Frequency %

http://insects.ippc.orst.edu/pnw/?weeds/id/Canada_thistle--Cirsium_arvense--s.i.html

http://images.google.dk/imgres?imgurl=http://www.mdwillowcreek.com/pics/canthistle.jpg&imgrefurl=http://www.mdwillowcreek.com/html/noxiousweed2.html&h=311&w=287&sz=18&hl=da&start=37&um=1&tbnid=dRqPC-XfHOICLM:&tbnh=117&tbnw=108&prev=/images%3Fq%3DCirsium%2Barvense%26start%3D20%26ndsp%3D20%26um%3D1%26hl%3Dda%26sa%3DN



Number of resistent biotypes

Senecio vulgaris



Number of resistant biotypes



Number of Resistant Biotypes





Seed cleaning

Improved techniques for crop seed cleaning have almost eradicated some species that werewidespread before the Second World War

Agrostemma githago

Steve Hurst @ USDA-NRCS PLANTS Database

Lolium temulentum



Mechanisation and changes in cultivation methods

Equisitum arvense Tussilago farfara Sonchus arvensis Elytrigia repens



Combine harvester favoured seed dispersal of certain therophytes

Some species shed seed later than the time at which reaping previous has been carried out but earlier than the present combine harvest:

Capsella bursa-pastorisChenopodium albumMatricaria discoidea Polygonum aviculareStellaria mediaTripleurospermum inodorum

http://storage.digitalkritik.dk/500009832_800x1200_d5565fe7ec563c6e5f754924841f77808f3be523.jpg



Mechanisation and changes in cultivation methods

Heavy machinery favour some species:

Chamomilla recutitaChamomilla suaveolensPlantago majorPoa annuaPolygonum aviculareTripleurospermum inodorum

http://www.claas.com/omaha/generator/cl-pw/us/home,lang=en_US-OMAHA.html

The germination of seeds of various weeds in relation to partial pressure of oxygen

(Müllerstedt, 1953)

100

80

60

40

20

0 2 4 6 8 10 12 14 16 18 20

Germination %

Oxygen %

Alopecurus myosuroides

Chenopodium album

Stellaria media

Poa annuaMatricaria chamomilla Avena fatua

Oxygen (%)

Presenter

Presentation Notes

Soil compaction may enforce a similar germination response to that of waterlogging by its effect on avaible oxygen in the soil.



Prohibition on straw-burning and reduced stubble cultivation could partly be responsible

for an increase in grass weeds



Different soil cultivation methods impose different weed flora



Reduced soil cultivation

Ordinary soil cultivation



Conclusion and outlook

• Several factors have operated in concert to influence changes in weed abundance

• Crop rotation, fertilization, mechanisation, management strategy and use of herbicides

• The common agricultural policy influence the farmers choice of crop and with it the weed flora

• Political initiatives to reduce side effects of pesticides and fertiliser will affect the weed flora



Thank you for your attention!

Technology

ChristianAndreasen_Prague_Jun11