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EC Oerke, unpublished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EC Oerke, unpublished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)