This document summarizes changes in weed flora in Denmark over the past 100 years. Surveys from 1911-1915, 1940-1945, 1960-1970, and 1987-1989 show changes in crop types and number of fields over time. Factors that have influenced weed abundance include crop rotation, fertilization, drainage, herbicides, seed cleaning, mechanization, legislation, and changes in cultivation methods. The average number of weed species found in crops has fluctuated over the decades. Specific weed frequencies have increased or decreased in different crops. Resistance to herbicides has also impacted some weed populations.
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ChristianAndreasen_Prague_Jun11
1. Department of Agriculture and Ecology
Weed flora changes in response
to weed control over the
last 100 years
Associate Professor Christian Andreasen
Department of Agriculture and Ecology
Crop Science
Prague, 14 June 2011
Dias 1
2. Department of Agriculture and Ecology
Weed surveys in Denmark
1911-15 1940-45 1960-70 1987-89 2001-04
l l l l l l l l l l l
1910 1930 1950 1970 1990 2010
Crops: 2 2 19 9 11
Fields:64 50 466 357 407
Prague, 14 June 2011
Dias 2
3. Department of Agriculture and Ecology
Average number of species among 67 weed species
surveyed in a single circle of 0.1 m2
8
1967-70
7
1987-89
6
5
4
3
2
1
0
Spring barley Spring rape Winter rye Winter wheat Grass leys
Prague, 14 June 2011
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4. Department of Agriculture and Ecology
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
Prague, 14 June 2011
Dias 4
5. Department of Agriculture and Ecology
Average number of species (±SD) recorded in a single
Raunkiær circle of 0.1 m2
Average number of weed species
12
1967-70
10 1987-89
2001-04
8
6
4
2
0
Spring Spring rape Winter rye Winter Grass ley Peas Fodder Sugar beets Winter
barley wheat beets barley
Prague, 14 June 2011
Dias 6
6. Department of Agriculture and Ecology
Changes in frequency of Poa annua
Frequency %
90
80
1987-89
70 2001-04
60
50
40
30
20
10
0
Sugar beets Fodder S. barley S. rape Peas w. barley W. wheat W. rye Grass leys
beets
Prague, 14 June 2011
Dias 7
7. Department of Agriculture and Ecology
Reasons for weed flora changes
during the last 100 year
• Crop rotation
• Fertilisation
• Drainage
• Herbicides
• Seed cleaning
• Mechanisation and changes in cultivation methods
• Legislation
Prague, 14 June 2011
Dias 8
8. Department of Agriculture and Ecology
Cluster analysis of crops based on frequency
of occurrence of all species in a Danish survey (2001-2004)
A B
C D
Prague, 14 June 2011
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9. Department of Agriculture and Ecology
Area of 10 crops as a fraction of the total arable
area in Denmark
Percentage of total
arable land
45
40 1967-70
1987-89
35
2001-04
30
25
20
15
10
5
0
Winter Spring Winter Winter Spring Maize Grass Sugar Fodder Winter
rye barley barley rape rape leys beets beets wheat
(From Andreasen & Stryhn, 2005)
Prague, 14 June 2011
Dias 10
10. Department of Agriculture and Ecology
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
Prague, 14 June 2011
Dias 11
11. Department of Agriculture and Ecology
New crops may create new weed problems!
Prague, 14 June 2011
Dias 12
12. Department of Agriculture and Ecology
Echinochlora sp. and Setaria viridis in maize
Prague, 14 June 2011
Dias 13
13. Department of Agriculture and Ecology
Red fescue (Festuca rubra) Vulpia bromoides
From:florabase.calm.wa.gov.au
Prague, 14 June 2011
Dias 14
14. Department of Agriculture and Ecology
Nitrogen and fertilisation
Average nitrogen fertilizer (kg/ha) used on arable land
200
180
160
140
120
100
80
60
40 N fertiliser (kg/ha)
20
0
1950 1960 1970 1975 1979
(from Haas & Streibig, 1982)
Commercial Dung and slugde N-fixation From air
Fertilizer slurry manure
Prague, 14 June 2011 (From: http://dmu.dk)
Dias 15
15. Department of Agriculture and Ecology
Nitrogen fertilisers favour nitrophilous species
Elytrigia repens
Poa annua
Chenopodium album
Stellaria media
Enhance the shading ability of crops
Shade tolerant species
Poa annua
Stellaria media
Viola arvense
Species able to elongate into more favourable light condition
Fallopia convolvulus
Galium aparine
Prague, 14 June 2011
Dias 16
16. Department of Agriculture and Ecology
Use of lime has tripled since 1950
Negative effect on calcifuge weed species:
Rumex acetosella
Scleranthus annuus
Spergula arvensis
Favour weed species like:
Veronica persica
Anagallis arvensis
Lamium purpureum
Prague, 14 June 2011
Dias 17
18. Changes in the dry weight production of
Galium aparine after spraying
with MCPA and Mecoprop
200
% of untreated
150
MCPA
100
Mecoprop
Mechlorprop
50
0
Control 0.5 l /ha 1.0 l/ha 2.0 l/ha
1,0l
(Petersen, 1960)
(From Petersen, 1960)
19. Department of Agriculture and Ecology
Dose response curve for a herbicide
Uncertainty Uncertainty
90% effect level
70% effect level
Per cent effect
Dose
Prague, 14 June 2011
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20. Department of Agriculture and Ecology
Changes in frequency of
Frequency % Elytrigia repens
18
16 1987-89
2001-04
14
12
10
8
6
4
2
0
pe
y
er ts
W ley
as
S. y
G rye
s
at
le
rle
et
dd ee
he
Pe
ra
ar
be
ss
ba
.
Fo r b
W
.w
.b
ra
ga
S.
W
Prague, 14 June 2011
Su
Dias 21
21. Department of Agriculture and Ecology
Changes in frequency
of Cirsium arvense
Frequency %
6
1987-89
5 2001-04
4
3
2
1
0
ys
S. ets
.b s
er ts
S. y
W ye
ra pe
pe
W t
.w y
a
W ea
rle
W rle
dd e e
he
le
.r
G ra
ra
be
P
ba
a
Fo r b
ss
.
ga
Su
Prague, 14 June 2011
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22. Department of Agriculture and Ecology
Number of resistent biotypes
Senecio vulgaris
Prague, 14 June 2011
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26. Department of Agriculture and Ecology
Seed cleaning
Improved techniques for crop seed cleaning
have almost eradicated some species that were
widespread before the Second World War
Steve Hurst @ USDA-NRCS PLANTS Database
Lolium temulentum
Agrostemma githago
Prague, 14 June 2011
Dias 27
27. Department of Agriculture and Ecology
Mechanisation and changes in cultivation methods
Equisitum arvense Tussilago farfara Sonchus arvensis Elytrigia repens
Prague, 14 June 2011
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28. Department of Agriculture and Ecology
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-pastoris
Chenopodium album
Matricaria discoidea
Polygonum aviculare
Stellaria media
Tripleurospermum inodorum
Prague, 14 June 2011
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29. Department of Agriculture and Ecology
Mechanisation and changes in cultivation methods
Heavy machinery favour some species:
Chamomilla recutita
Chamomilla suaveolens
Plantago major
Poa annua
Polygonum aviculare
Tripleurospermum inodorum
Prague, 14 June 2011
Dias 30
30. The germination of seeds of various weeds in
relation to partial pressure of oxygen
Germination %
100 Alopecurus myosuroides
80
Avena fatua
60 Matricaria chamomilla
Poa annua
40
Stellaria media
20
Chenopodium album
0 2 4 6 8 10 12 14 16 18 20 Oxygen %
Oxygen (%)
(Müllerstedt, 1953)
31. Department of Agriculture and Ecology
Prohibition on straw-burning and reduced
stubble cultivation could partly be responsible
for an increase in grass weeds
Prague, 14 June 2011
Dias 32
32. Department of Agriculture and Ecology
Different soil cultivation methods impose different weed flora
Prague, 14 June 2011
Dias 33
33. Department of Agriculture and Ecology
Ordinary Reduced
soil cultivation soil cultivation
Prague, 14 June 2011
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34. Department of Agriculture and Ecology
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
Prague, 14 June 2011
Dias 35