agroecosystem management weed2013
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AgricultureTRANSCRIPT
Agro-ecosystem management
and analysis at farm scale
Weeds and weed control
Per Kudsk
Department of Agroecology
Outline
• Introduction – Why do we need to control weeds, diseases and pests?
• Weed biology
• Weed population dynamic
• Weed competition
• Weed control – Preventive methods
– Non-chemical methods
– Chemical weed control
• Decision support system (Plant Protection Online)
Introduction
Potential and actual yield
Potential yield
Attainable yield
Actual yield
Water
Nitrogen
Phosphorus
CO2
Light intensity
Temperature
Crop
Weeds
Diseases
Pests
Goudriaan & Zadoks (1995)
Foto: Knud Tybirk
Pests and yield losses
Oerke, 2006
346.5 M t
40.6 M t 22.1 M t
92.5 M t
31.4 M t
25.4 M t
37.8 M t
29.3 M t 30.0 M t
180.6 M t
41.5 M t
0.780
0,610
0.632
0.424
0.583
0.447
0.523
0.691
0.560
0.691 0.805
0.822
0.349
0,349
0.312
0.248
0.255
0.255
0.237
0.286
0.247
0.300 0.354
0.417
Effect of Pests and Crop Protection on Maize Production, 2002-04
Production potential
940.3 x 106 t (= 100%)
Production without control
296.7 x 106 t (= 31.6%)
Production with control
648.5 x 106 t (= 69.0%)
Loss potential 68.4% Actual losses 31.0%
EC Oerke, unpublished
272.7 M t
303.9 M t 272.7 M t
17.4 M t
22.8 M t
11.6 M t
12.5 M t
0.71
0.57 0.64
0.24
0.22 0.23
Effect of Pests and Crop Protection on Rice Production, 2002-04
Production potential
922.7 x 106 t (= 100%)
Loss potential 77.0% Actual losses 36.3%
EC Oerke, unpublished
Production with control
588.0 x 106 t (= 63.7%)
Production without control
211.9 x 106 t (= 23.0%)
Bichel Committee
• Committee on assessing the overall consequences of a
partial or total
phasing-out of pesticide use (1997-98)
• Main committee and 4 sub-committees
• Sub-committee on agriculture
• Sub-committee on production, economics and
employment
• Sub-committee on health and the environment;
• Sub-committee on legislation
Bichel Committee
• Bichel Committee examined 3 scenarios:
– Optimised use of pesticides (+scenario)
• 31% reduction in pesticide use
• No adverse economic impact on agriculture
– Limited use of pesticides (++scenario)
• 80% reduction in pesticide use
• 8-23% reduction in the net profit margin
• 8% reduction in the Gross Domestic Product at factor costs
• 0,4% reduction in the Gross Domestic Product
– Phasing out of pesticides (0-scenario)
• 20-50% reduction in the net profit margin
• 15% reduction in the Gross Domestic Product at factor costs
• 0,8% reduction in the Gross Domestic Product
Bichel Committee
0 10 20 30 40 50 60
Grassland
Oilseed rape
Winter rye
Sugar beets
Spring barley
Peas
Winter barley
Winter wheat
Potato
Grass seed
Percent yield loss
0-scenario
Bichel Committee
0 20 40 60 80 100
Cherry
Strawberry
Blackberry
Pear
Apple
0-scenario
Percent yield loss
Weed biology
What is a weed?
• ”a plant which virtues have yet to be discovered”
• ”an unwanted plant” (unkraut, malherbe, ukrudt)
• ”any plant or vegetation excluding fungi, interfering with
objectives or requirements of people” (European Weed
Research Society)
Reasons for defining a plant as a weed
• Reduce crop yields
• Reduce crop quality
• Delay and interfere with harvesting
• Interfere with animal feeding
• Cause poisoning
• Taint animal products
• Plant parasites
• Reduce crop health
• Reduce animal and human health
• Safety hazard
• Reduce wool quality
• Prevent water flow
• Exhibit allelopathy
• Impact on crop establishment
Galium aparine in wheat
Senecio jacobaea in grassland
Cympobogon afronardus in grassland
Fallopia convolvolus Ambrosia artemisiifolia
Striga hermontica on maize
What are the characteristics of a
succesfull weed (“Baker’s rule”)
• Germination in many environments
• Self-controlled germination and great longevity of seeds
• Rapid seedling growth
• Early onset of seed production
• Long period of seed production
• Self-compatibility
• Easy cross-pollination
• High seed output (under favourable conditions)
• Long and short-distance dispersal of seeds
• Competitive Baker (1965)
Generation time of weeds
• Annual weeds
– Winter annuals (germinate in the autumn and produce seeds in
the spring) (e.g. Centaurea cyanus, Apera spica-venti)
Germination
Flowering
Germination
Flowering
Generation time of weeds
• Annual weeds
– Summer annuals (germinate and produce seeds in the spring) (e.g. Chenopodium album, Solanum nigrum)
Germination Germination
Flowering Flowering
Generation time of weeds
• Annual weeds
– Facultative winter annuals (germinate either spring or autumn and
produce seeds the following summer) (e.g. Stellaria media, Poa annua)
Germination
Flowering
Germination
Flowering
Generation time of weeds
– Perennial weeds
Year 1 Winter Year 2 Year 1 Winter Year 2
Reproduction by seeds e.g.
Taraxacum officinale, Rumex sp.
Reproduction by vegetative organs e.g.
Circium arvensis, Elytrigia repens
Crops and weeds are associated
• Strictly autumn-germinating weed species normally only
found in autumn-sown crops (e.g. Apera spica-venti,
Centaurea cyanus and Papaver rhoaes)
• Strictly spring-germinating weed species only a problem
in autumn-sown crop if the crop competes poorly
• Many weeds germinate both autumn and spring
(”facultative winter annuals”) and can survive and
produce seeds in both autumn- and spring-sown crops
Weed frequency in crops
Winter wheat Winter rye Grass seed
crops 1987-89 2001-04 1987-89 2001-04 1987-89 2001-04
A. spica-
venti
2,4% 15,8% 6,8% 26,8% 0% 0%
P. annua 38,1% 61,1% 22,1% 57,3% 46,8% 60,2%
Andreasen & Stryhn (2008). Weed Research 48, 1-9
Soil seed bank
Young plants
Mature plants
Life cycle of a weed
Soil seed bank
• Reservoir of viable seeds (for perennial weeds it is a bank of
vegetative organs e.g. buds)
• Seed banks typically contain from 1000 to 80000 seeds per m2
(lowest number in pastures and intensively managed fields)
• Seed not uniformly distributed in the field which gives rise to non-
uniform weed stands
• Number of seeds often lower on clay than on sandy soils
• Three types of seed banks:
– Transient (less than 1 year, Senecio vulgaris and some grass species)
– Short-term persistent (1-5 years, e.g. Viola arvensis)
– Long-term persistens (>5 years, e.g. Papaver rhoaes, Polygonum sp.)
• 0.5-5% of the seeds germinate every year
Soil seed bank dynamics
Grundy & Jones 2002
Seed dormancy
• Dormancy is ”a barrier preventing germination when conditions
would normally be favourable”
• Fresh seeds have primary dormancy (requirement for after-
ripening). Primary dormancy is regulated by genetics and
environment
• Conditional dormancy follows primary dormancy. The rate of
germination will graudually increase and the requirement to the
conditions for germination will decrease
• Conditional dormancy ensures that seeds primarily germinates
when conditions are optimum (e.g. autumn versus spring)
• Seeds may go from primary to conditional and back to primary
dormancy
Dormancy
Radosevic et al. 2007
Germination
• Soil moisture influence the germination of most weed species
• Many weed species with small seeds require light induction for
germination (prevents fatal germination from depths from which the
seedling cannot survive)
• Alternating temperatures indicating closeness to the soil surface
probably also affects germination
Effect of tillage on germination
Radosevic et al. 2007
Seed production
• Seed production varies significantly between weed
species:
– Poa annua 500 seeds/plant
– Solanum nigrum 500 seeds/plant
– Alopecurus myosuroides 600 seeds/plant
– Sinapis arvensis 1,000 seeds/plant
– Apera spica-venti 5,000 seeds/plant
– Stellaria media 15,000 seeds/plant
– Chenopodium album 20,000 seeds/plant
– Tripleurospermum perforatum 34,000 seeds/plant
– Papaver rhoeas 41,000 seeds/plant
Seed persistence
Weed species Cultivated soil Non-cultivated soil
Tripleurospermum inodorum 10 23
Fallopia convolvolus 10 26
Chenopodium album 9 53
Polygonum aviculare 8 39
Poa annua 8 24
Viola arvensis 7 38
Papaver rhoaes 7 21
Stellaria media 4 22
Capsella bursa-pastoris 4 23
Spergula arvensis 2 13
Veronica arvensis 1 33
Senecio vulgaris 0,3 13
% germination after 6 years
Robert & Feast 1973
The fact that weeds originates from seeds in the soil seed
bank makes weeds a chronic problem in contrast to most
diseases and pests which can be characterised as epidemic
problems. The long-term aspect of weed control strongly
influences the attitude of farmers and advisors to weed
control practices
Weeds are different from most
diseases and pests
Weed population dynamics
Weed population dynamics
• Annual cycle vs. sequence of annual cycles
K
Nt = ------------------------
1 + (K/No -1)e-rt
Nt = number of individuals at time t
No = number of individuals at time zero
K = the carrying capacity of the system
r = the maximum unrestricted population growth rate
t = time
K=ceiling population
r =maximum growth rate
Norris et al. 2007
Germination over time
0
25
50
75
100
4-10 90 23-11 90 12-1 91 3-3 91 22-4 91
Date
Accu
mu
late
d g
erm
inati
on
(%
)
Rævehale1 - 60 Vindaks1 - 21A. myosuroides A. spica-venti
Life cycle flow diagram
Radosevic et al. 2007
Crop-weed competition
Crop-weed competition
Radosevic et al. 2007
Efter Conn & Thomas, 1987 og Wilson m.fl., 1995)
Yie
ld lo
ss
%
Papaver rhoeas 1988
Papaver rhoeas 1989
Chenopodium album 1986
Number of weed plants per m2
Yield loss vs. Apera spica-venti density Summary of winter wheat trials conducted by DAAS 1997-2007
y = 3,7388Ln(x) - 0,6274
R2 = 0,1274
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150 200 250 300
Apera spica-venti plants/m2
Yie
ld lo
ss (
hkg
/ha)
Critical period for weed control
Radosevic et al. 2007
Critical period for weed control Organic winter wheat
Welsh et al. 1999
Critical period for weed control Organic winter wheat
Welsh et al. 1999
Weed free
Weed free Weed infested
Weed infested
Weed control
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
Crop rotation
0
50
100
150
200
250
300
0 25 50 100
0
50
100
150
200
250
300
0 25 50 100
Ploughing
Herbicide dose, % af standard dose
50% winter annual crops 100% winter annual crops
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
• Choice of cultivar
Competitive wheat variety Non-competitive wheat variety
Crop competitiveness
Christensen 1994
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
• Choice of cultivar
• Crop establisment
Sowing date of winter wheat
Christensen 1993
Sowing density of winter wheat
Christensen 1993
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
• Choice of cultivar
• Crop establisment
• Plant spacing
Uniform plant spacing
= crop plant
(Fra Weiner et al., 2001)
Plant spacing
Planting in rows
Crop evenly distributed
Weed
bio
mass (
g/m
2)
Sowing rate (seed pr. m2)
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
• Choice of cultivar
• Crop establisment
• Plant spacing
• Cultivation
Crop rotation
0
50
100
150
200
250
300
0 25 50 1000
50
100
150
200
250
300
0 25 50 100
Ploughing
No ploughing
Herbicide dose, % af standard dose
50% winter annual crops 100% winter annual crops
Preventive measures
• Crop rotation
– Annual vs. perennial crops, winter vs. spring annual crops, cover
crops etc.
• Choice of cultivar
• Crop establisment
• Plant spacing
• Cultivation
• Preventing introduction of weeds
Introduction of new weed species
• Vulpia sp. is an increasing problem in grass seed crops
0
78
148
0 2 1
0
20
40
60
80
100
120
140
160
No
. P
an
icle
s/
m-2
in
Ju
ly
W. wheat 40% spring crops
Ploughing Harrowing No tillage
Non-chemical weed control
Chemical weed control
Profile
Products
Evaluation
Screening
5000
1 - 2
30
Time
100.000
Classification of herbicides by use
Selective
Foliage applied
Contact (e.g. ioxynil)
Translocated (e.g. SU herbicides)
Soil applied
Foliage applied
Soil applied
Non-selective
Non-mobile (e.g. prosulfocarb)
Translocated (e.g. metamitron)
Contact (e.g. diquat)
Translocated (e.g. glyphosate)
Non-mobile (e.g. fumigants)
Translocated (e.g. simazin)
Herbicide selectivity
• Selectivity
– Metabolism in the crop
– Herbicide dose (differences in retention on the leaves,
differences in depth of germination)
– Time of application (before crop emergence, crop dormant)
Herbicide selectivity
Herbicide
Herbicide activity
• Weed spectrum – Broad-spectrum herbicides (dicot and monocot weeds)
– Narrow-spectrum herbicides (typically monocot weeds)
Herbicide activity
0
10
20
30
40
50
60
70
80
90
100
T. in
odor
um
S. m
edia
V. a
rven
sis
V. p
ersi
ca
P. a
vicu
lare
1/16 N
1/8 N
1/4 N
1/2 N
1 N
Chlorsulfuron Ioxynil+bromoxynil
0
10
20
30
40
50
60
70
80
90
100
Perc
en
t co
ntr
ol
Factors affecting herbicide activity
• Weed flora
• Weed growth stage
• Crop competiveness
• Soil type
• Climatic conditions (temperature, humidity, light, rain etc.)
• Application technique (including water quality)
Herbicide resistance
Glyphosate resistant crops
EU’s new pesticide legislation
72
Regulation 1107/2009
replacing Directive
91/414/EEC
Directive 2009/128/EC
on the sustainable use of
pesticides
Regulation 1185/2009 on
the collection on
statistics on PPP
COM(2006) 778 final
Directive 2009/127/EC
on the placing on the
market of pesticide
application equipment
EU Direktive 128/2009
• Training of professional users, distributors and advisors
• Inspection of spray equipment in use
• Specific measures to protect the aquatic environment and drinking water
• Reduction of pesticide use or risks in specific areas
• Harmonized pesticide indicator
• National Action Plan before 1/12-2012
• Integrated Pest Management should be applied by all professional users of
pesticides by 1/1-2014
73
Definitions of IPM
• 65 definitions of IPM (Ehler, 2006)
• "IPM is a sustainable approach to managing pests by combining
biological, cultural and chemical tools in a way that minimises
economic, environmental and health risks” (ENDURE, 2008)
• “ENDURE sees Integrated Pest Management (IPM) as
a continuously improving process in which innovative
solutions are integrated and locally adapted as they emerge and
contribute to reducing reliance on pesticides in agricultural systems”
74
The 8 IPM principles
1. Harmfull organisms should be prevented e.g. by crop rotation,
adequate cultivation techniques, resistent/tolerant varieties and
protection of beneficial organisms
2. Harmful organisms must be monitored by adequate methods and
tools, where available. Such adequate tools should include
observations in the field as well as scientifically sound warning,
forecasting and early diagnosis systems
3. Based on the results of the monitoring the professional user has to
decide whether and when to apply plant protection measures.
Robust and scientifically sound threshold values are essential
components for decision making.
4. Sustainable non-chemical control methods should be preferred to
chemical methods if they provide satisfactory control
The 8 IPM principles
5. Apply pesticides specific for the target with the least side effects on
human health and the environment
6. Use of pesticides and other forms of intervention should be kept to
levels that are necessary, e.g. by reduced doses, reduced
application frequency or partial applications
7. Available anti-resistance strategies should be applied to maintain
the effectiveness of the products. This may include the use of
multiple pesticides with different modes of action.
8. Based on the records on the use of pesticides and on the
monitoring of harmful organisms the professional user should
check the success of the applied plant protection measures.
76
Crop Protection Online (CPO)
Crop Protection Online (CPO)