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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 2
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 3
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 4
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 6
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 7
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
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Prague, 14 June 2011Dias 8
Reasons for weed flora changes during the last 100 year
• Crop rotation • Fertilisation• Drainage• Herbicides• Seed cleaning• Mechanisation and changes in cultivation methods• Legislation
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 9
Cluster analysis of crops based on frequency of occurrence of all species in a Danish survey (2001-2004)A B
C D
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Prague, 14 June 2011Dias 10
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)
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Prague, 14 June 2011Dias 11
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
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Prague, 14 June 2011Dias 12
New crops may create new weed problems!
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Prague, 14 June 2011Dias 13
Echinochlora sp. and Setaria viridis in maize
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Prague, 14 June 2011Dias 14
Red fescue (Festuca rubra) Vulpia bromoides
From:florabase.calm.wa.gov.au
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 15
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)
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Prague, 14 June 2011Dias 16
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
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Prague, 14 June 2011Dias 17
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
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Prague, 14 June 2011Dias 18
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)
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Prague, 14 June 2011Dias 20
70% effect level
90% effect levelU
ncer
tain
tyU
ncer
tain
ty
Dose response curve for a herbicide
Dose
Per
cent
effe
ct
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Prague, 14 June 2011Dias 21
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 %
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 22
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 %
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Prague, 14 June 2011Dias 23
Number of resistent biotypes
Senecio vulgaris
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Prague, 14 June 2011Dias 24
Number of resistant biotypes
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Number of Resistant Biotypes
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Prague, 14 June 2011Dias 26
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 27
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
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Prague, 14 June 2011Dias 28
Mechanisation and changes in cultivation methods
Equisitum arvense Tussilago farfara Sonchus arvensis Elytrigia repens
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 29
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 30
Mechanisation and changes in cultivation methods
Heavy machinery favour some species:
Chamomilla recutitaChamomilla suaveolensPlantago majorPoa annuaPolygonum aviculareTripleurospermum inodorum
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 (%)
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 32
Prohibition on straw-burning and reduced stubble cultivation could partly be responsible
for an increase in grass weeds
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 33
Different soil cultivation methods impose different weed flora
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 34
Reduced soil cultivation
Ordinary soil cultivation
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 35
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
Department of Agriculture and Ecology
Prague, 14 June 2011Dias 36
Thank you for your attention!
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