Module M 3801-420:
Crop Production Systems
I: Pest and weed Management
and
Dr. Abuelgasim Elzein
University of Hohenheim,
Institute of Plant Production and Agroecology in the Tropics and
Subtropics; Email: gasim@uni-hohenheim.de
Contents
1. Yield losses caused by pests, diseases and weeds
2. Pests and diseases of rice and cassava: examples
3. Principles of IPM
4. General aspects of weed control
5. Principles of biological pest and weed control
Estimated losses of the 8 most important food- and
market-crops1 during the period 1988 - 90,
analysed per continent
Continent
Losses (%)3
Production
Total losses
($ billions)
(%)
Diseases
Pests
Weed
Africa
13,3
4,02
15,6
16,7
16,6
48,9
12,8
North
America
50,5
15,1
9,6
10,2
11,4
31,2
23,0
Latin
America
30,7
9,2
13,5
14,4
13,4
41,3
21,8
162,9
48,6
14,2
18,7
14,2
47,1
145,3
Europe
42,6
12,7
9,8
10,2
8,3
28,2
16,8
U.S.S.R.
31,9
9,5
15,1
12,9
12,9
40,9
22,1
Ozeania
3,3
1,0
15,2
10,7
10,3
36,2
1,9
335,2
100,0
13,3
15,6
13,1
42,1
Asia
Total
(%) ($ billions)
(Oerke et al., 1994)
1
2
3
Rice, wheat, barley, maize, potatos, soja, cotton, coffee
Percental part of the worlproduction
Percental part of an achieved production
243,7
Yield losses caused by pests, diseases and weeds
Crop
Yield losses (%)
Diseases
Pests
Weeds
Total
Rice
15,1
20,7
15,6
51,4
Wheat
12,4
9,3
12,3
34,0
Barley
10,1
8,8
10,6
29,4
Maize
10,8
14,5
13,1
38,3
Potato
16,4
16,1
8,9
41,4
Soybean
9,0
10,4
13,0
32,4
Cotton
10,5
15,4
11,8
37,7
Coffee
14,9
14,9
10,3
40,0
Mean
12,4
13,8
12,0
38,1
(Oerke et al 1994)
Insect pests in rice:
Hopper burn –
outbreakes of
leafhoppers
Sogatodes spp.
Asia
Control: systemic insecticides
Insect pests in rice:
Rice bug:
Leptocorisa oratoria
Sucking damage at glumes, shrinking
and drying up panicles andg grains
Eggs
Nymph
Control: rotation, planting time
Insecticides
Adult
Cassava - Diseases and pests
African mosaic virus
Virus transmited by insect
(Bemisia tabasi)
Symptoms: yellowish leaves
Control:
1. Use of rsistance cultivars
2. Chemical and other means of
control of the vector instect
Strategies in crop protection
1.
2.
3.
4.
5.
6.
Preventive measures (plant guarantine)
Cultural or agronomical control
Physical control
Chemical control
Biological control
Integrated pest mamagement
Insect pests in rice:
Rice bug:
Leptocorisa oratoria
Sucking damage at glumes, shrinking
and drying up panicles andg grains
Eggs
Nymph
Control: rotation, planting time
Insecticides
Adult
Green rice bug –
Nezara viridula
Eggs
5. Nymphal stage
Adults
Definitions of Integrated Pest Management
“IPM”
FAO definition
„A pest management system
that, in the context of the
associated environment and
the population dynamics of
the pest species, utilises all
suitable
techniques
and
methods in as compatible
manner as possible and
maintains the pest population
at levels below those causing
economically
unacceptable
damage or loss”
German Plant Protection Law
„A
combination
of
techniques which, giving
preference to biological,
biotechnological,
plantbreeding, cultivation and
cropping methods, restricts
the application of chemical
pesticides to the necessary
minimum“
Principles of IPM
• IPM is a holistic, interdisciplinary approach
which considers the ecological and socioeconomic conditions of a site as one unit, and
strives to maintain the productivity of the
agroecosystem on a sustainable basis.
• Measures to control pest infestation take into
account
all
anticipated
ecological,
toxicological
and
economic
impacts:
preference is given to non-chemical methods
over the application of chemical pesticides.
What are “weeds”?
Weeds are plants that cause more damage than use.
“Weeds” are internationally defined as all not desired
plant species of very different habitats.
Apart from weeds of agricultural crops and pastures or
respectively aquatic systems, not desired trees and
shrubs of the natural vegetation are defined in this way,
too.
Why weed control?
• Qualitative yield reduction
- pollution of harvest products by weed seeds
• Quantitative yield reduction
- competition for growth factors (nutrients, water, light)
Weed competition during the
emergence of potatoes
Why weed control?
• Difficulties concerning cultivation- and harvest labour
Flaveria trinerva infestation at potato cropping in the Republic of
Yemen
Why weed control?
• Toxic effect of pasture weeds
• Favourable conditions for the transmission of plant
diseases and pests
-hosts or intermediate host
Solanum nigrum parasitized by
Orobanche cernua
Why weed control?
• Displacement of endemic species through accidentally
imported plants
Eichhornia crassipes
Pistia stratiotes
Positive effect of weeds
• Better soil tilth (tillage), and erosion protection by shading
and root penetration of the soil
• Support of the beneficial fauna (permanent crops annual
crops)
Segetal vegetation besides
fields in potato production
in the Republic of Yemen
Positive effect of weeds
• Weeds used as additional forage source esp. for smallholder systems of the semi-arid tropics and subtropics
Use of Echinops spp. in
semi-arid regions of the
Republic of Yemen
• Weeds as medicinal crops
• Weeds as green manure
• Weeds as potential genetic pools for crop breeding
Instruments for weed control
1. Preventive measures (seed cleaning, crop
residues, machines and equipment)
2. Mechanic measures (hoe, harrow, weed harrow)
3. Physical measures (flaming, solarisation)
4. Chemical measures (herbicides)
5. Biological measures (insects, pathogens)
Basic components of weed control
1. Identification of weeds and their level of infestation
2. Biology and ecology of the weed species
3. The competitive effects and economic thresholds
4. Technically effective, economically viable and
environmentally safe methods of control
The most serious weeds in the world
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Species
Cyperus rotundus L.
Cynodon dactylon (L.) Pers
Echinochloa curs-galli (L.) P. Beauv.
Echinochloa colona (L.) Link
Eleusine indica (L.) Gaertn.
Sorghum halepense (L.) Pers
Imperata cylindrica (L.) Rauschel
Eichhornia crassipes (Mart.) Solms
Portulaca oleraceae L.
Chenopodium album L.
Digitaria sanguinalis (L.) Scop.
Convolvulus arvensis L.
Avena fatua L. and relatives
Amaranthus hybridus L.
Amaranthus spinosus L.
Cyperus esculentus L.
Paspalum conjugatum Berg
Rottboellia cochinchinensis
(Lour.) W.D. Clayton
Growth form
P
P
A
A
A
P
P
P
A
A
A
P
A
A
A
P
P
A
M
M
M
M
M
M
M
D Aq.
D
D
M
D
M
D
D
M
M
M
* A = annual; Aq = aquatic; D = dicotyledon; M = monocotyledon; P = perennial
Module M 3801-420:
Crop Production Systems
II: Principles of biological pest and weed control
and
Dr. Abuelgasim Elzein
University of Hohenheim,
Institute of Plant Production and Agroecology in the Tropics and
Subtropics; Email: gasim@uni-hohenheim.de
Biological Control
•What is Biological Control: definitions
•Historical Background
•Why is biological control
•Principles
•Biological control mechanisms
•Selected successful examples:
–Plant diseases
–Insects
–Nematodes
–weeds
What is Biological Control?
• Definitions:
The utilisation of organisms (micro or macro) for
the regulation of plant pests (weeds, diseases,
insects, nematodes) densities below the economic
threshold.
• The use of parasitoids, predators, pathogens and
competitors to supress a pest population, making
it less abundant and thus less damaging than it
would otherwise be.
What is Biological Control?
A Microbiologist’s Perspective
Pest suppression with biological agents operating in a
background of integrated control that does not depend
on host resistance, sterilization of the target pathogen,
or modification of pest behavior.
A Practical Perspective
Pest suppression with biological agents, derivatives of,
or products of biological agents applied in a background
of integrated control.
Is Biological Control Biotechnology?
Biotechnology is a set of tools that utilize living
things (and more recently, derivatives of living
things) to solve problems or to produce products.
Of course it is!
Historical Background
• The term biological control was first used by Smith (1919)
to describe the introduction of exotic natural enemies for
the permanat supression of insect pest.
• BC was first applied, long before its definition, when man
began keeping cats to protect stored grain from damag by
rodents.
• During the Pre-Scientific Era (Pre – 1880), in China and
Yeman colonies of ants were introduced and relaesed in
order to control citrus and date pests.
• During the 19th century, after microbes were discovered
and insects life cycle began to be understood, some
attempts were made to use other kind of organisms.
A chronology
of biological control
What Kinds of Things Function
as Biological Control Agents?
• Microorganisms
– Bacteria
– Fungi
– Nematodes
– Viruses
• Macroorganisms
– Insects
– Man
– Animals
Concept of biological control of pest
• To introduce natural enemies of a target pest
that will reduce and supress the density of the
pest to a level that is acceptable (threshold
level).
Natural enemies of pests (1)
Pathogens (include viruses,
bacteria, fungi and protozoa)
cause infection diseases in
their host which lead to their
death.
Beauveria infected beetle
Natural enemies of pests (2)
Parasitoides put the host to death during their development:
Egg parasitoids, larval parasitoids, adult and nymphal parasitoids
Aphelinus spp. parasitizing an aphid
Natural enemies of pests (3)
• Predators kill their prey
after catching. They need
more than one prey for its
development.
Coccinella septempunctata
Where do you find BC agents?
•
•
•
•
•
Suppressive soils
Old world
New world
On plant materials
On “sick” pathogens
and pests
• By accident
Suppressive soil:
A soil in which certain
disease(s) fail to develop
because of the presence of
microorganisms in the soil
antagonistic to the
pathogen.