ChristianAndreasen_Prague_Jun11

Department of Agriculture and Ecology

Weed flora changes in response
to weed control over the
last 100 years

Associate Professor Christian Andreasen
Crop Science

Prague, 14 June 2011
Dias 1


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

Dias 2


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
Dias 3


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

Dias 4


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

Dias 6


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
Dias 7


Reasons for weed flora changes
during the last 100 year

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

Dias 8


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

C D

Dias 9


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)

Dias 10


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
Dias 11


New crops may create new weed problems!

Dias 12


Echinochlora sp. and Setaria viridis in maize

Dias 13


Red fescue (Festuca rubra) Vulpia bromoides

From:florabase.calm.wa.gov.au

Dias 14


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


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

Dias 16


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

Dias 17


The effect of herbicides

Dias 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)


Dose response curve for a herbicide
Uncertainty Uncertainty
90% effect level

70% effect level
Per cent effect

Dose
Dias 20


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

Su

Dias 21


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

Dias 22


Number of resistent biotypes

Senecio vulgaris

Dias 23


Number of resistant biotypes

Dias 24


Number of Resistant Biotypes

Dias 25


Dias 26


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

Dias 27


Mechanisation and changes in cultivation methods

Equisitum arvense Tussilago farfara Sonchus arvensis Elytrigia repens
Dias 28


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

Dias 29


Mechanisation and changes in cultivation methods

Heavy machinery favour some species:

Chamomilla recutita
Chamomilla suaveolens
Plantago major
Poa annua
Polygonum aviculare
Tripleurospermum inodorum

Dias 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)


Prohibition on straw-burning and reduced
stubble cultivation could partly be responsible
for an increase in grass weeds

Dias 32


Different soil cultivation methods impose different weed flora

Dias 33


Ordinary Reduced
soil cultivation soil cultivation

Dias 34


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

Dias 35


Thank you for your attention!

Dias 36

ChristianAndreasen_Prague_Jun11

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