1. COURSE: Major crop insect pests and Diseases
Course credit: 2(2+0)
Course Code: (AGRN551)
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2. Chapter One: Introduction, and
Concept of crop Protection
Definition of pest
What's pest ?
• Pest definitions, kinds and outbreaks
Pest is derived from French word ‘Peste’ and Latin term ‘Pestis’
meaning epidemic or infectious organisms.
Pest is anything that:
competes with humans, domestic animals, or desirable plants for
food or water,
injures humans, animals, desirable plants, structures, or
spreads disease to humans, domestic animals, wildlife, or
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3. • Pest is which impose burdens on human population by
Injury to crop plants, forests and ornamentals
injury and death to humans and domestic animals
Destruction or value decline of stored products.
Types of Pests
insects, such as roaches, termites, mosquitoes, aphids,
beetles, fleas, and caterpillars.
insect-like organisms, such as mites, ticks, and spiders,
microbial organisms, such as bacteria, fungi, nematodes,
viruses, and mycoplasmas,
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4. Weeds, which are any plants growing where they are
mollusks, such as snails, slugs, and shipworms, and
vertebrates, such as rats, mice, other rodents, birds,
fish, and snakes.
Most organisms are not pests.
A species may be a pest in some situations and not in
An organism should not be considered a pest until it is
proven to be one.
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5. CATEGORIES OF PESTS
Based on their occurrence: -
• Regular pest: Frequently occurs on crop
-A pest that occurs every crop season and causes yield losses.
-Close association e.g. Rice slem borer, Brinjal fruit borer
• Occasional pest: Infrequently occurs on crops
-No close association e.g. Mango stem borer
• Seasonal pest: Occurs during a particular season every year e.g.
• Persistent pests: Occurs on the crop throughout the year and is difficult
to control e.g. Chilli thrips, mealy bug on guava
• Sporadic pests: Pest occurs in isolated localities during some period.
-A pest that is irregular but occasionally causes problems.
-It is a pest that occurs here and there in an irregular or random
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6. Potential pest: A pest that could become highly noxious if
allowed to establish.
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Categories of Pests Based on Infestation Level
Epidemic pest: Sudden outbreak of a pest in a
severe form in a region at a particular time e.g.
BPH in Tanjore, RHC in Madurai, Pollachi
Endemic pest: Occurrence of the pest in a low
level in few pockets, regularly and confined to
particular area e.g. Rice gall midge, Mango
7. CATEGORIES OF PEST BASED ON EIL, GEP AND DB
(i) Key pest - Most severe and damaging pests
• - GEP lies above EIL always
• - Spray temporarily bring population below EIL
• - These are persistent pests
• - The environment must be changed to bring GEP below
EIL e.g. Cotton bollworm, Diamond backmoth
(ii) Major pest:Many insects feed on our crops but all are
To be designated as pest, an insect must be responsible for
an economic yield loss of at least 5% (Misra, 1991).
Insects are categorized into major and minor pests based on
the percentage economic yield loss they cause.
Major pests are those that cause damage over 10%.
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8. (iii) Minor pest/Occasional pest:
• are those that cause damage between 5% to 10%.
• Damages below 5% are tolerable and often negligible.
• - GEP is below the EIL usually
• - Rarely they cross EIL
• - Can be controlled by spraying e.g., Cotton stainers,
Rice hispa, Ash weevils
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9. (iv) Sporadic pests
• - GEP generally below EIL
• - Sometimes it crosses EIL and cause severe loss in some
places/periods e.g., Sugarcane pyrilla, White grub, Hairy
(v) Potential pests - They are not pests at present
• - GEP always less than EIL
• - If environment changed may cause economic loss
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10. Parameters of Insect Population Levels
General equilibrium position (GEP)
The average density of a population over a long period of
time, around which the pest population over a long period
around which the pest population tends to fluctuate due to
biotic and abiotic factors and in the absence of permanent
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11. Economic threshold level (ETL): - Population density at
which control measure should be implemented to prevent
an increasing pest population from reaching the ETL.
is always less than EIL. Provides sufficient time for
Economic injury level (EIL): - The lowest population
density that will cause economic damage
Damage boundary (DB): - The lowest level of damage
which can be measured.
Equilibrium position (EP):-A condition in which all
acting influences are canceled by others, resulting in a
stable, balanced, or unchanging system.
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12. Pest population and concepts of injury level
The EIL, was the lowest population density that will cause economic
is the most basic of the decision rules; it is a theoretical value that, if
actually attained by a pest population, will result in economic
is a measure against which we evaluate the destructive status and
potential of a pest population.
Although the EIL is expressed as a pest density, it is actually a level
of injury that is indexed by pest numbers.
We use insect numbers for practicality, i.e., it is usually easier to
count pests rather than to quantify and project future injury.
The relationship of the EIL to the damage boundary is shown in
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13. Figure 1. The relationship of the DB to EIL
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14. • EIL is actually a degree of injury, it is sometimes useful to
think of it in terms of injury equivalents.
• An injury equivalent is the total injury produced by a single
pest over an average lifetime.
• It is a potential value, i.e., a pest dying prematurely will
obtain only a partial equivalent.
• The concept of using injury equivalents is particularly
appropriate when working with populations having discrete
generations and when trying to account for mortality and
its effect on total injury.
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15. If numbers alone are used, the economic threshold may need to
be positioned above the EIL early in a generation to account for
When using injury equivalents, the economic threshold is
always below the EIL.
Injury equivalents have also been used to develop EILs for
complexes of insect pests with similar feeding behaviors.
Whether expressed as numbers or injury equivalents, the EIL is
governed by five primary variables:
Cost of the management tactic per production unit, (C),
Market value per production unit (V),
Injury units per pest(I),
Damage per injury unit (D), and
The proportional reduction in pest attack (K).
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16. If the relationship of these variables is linear or roughly
so, the EIL can be given as:
EIL = C/VIDK
The EIL equation is a truly unifying principle of IPM.
As such, the equation provides a basis for strategic
decisions on IPM research priorities and for development
of environmentally sustainable management systems.
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17. Economic threshold level
The economic threshold (ETL) differs from the EIL.
it is a practical or operational rule, rather than a theoretical one.
"the population density at which control action should be
determined (initiated) to prevent an increasing pest population
(injury) from reaching the economic injury level.“
Although measured in insect density, is actually a time to take
action, i.e., numbers are simply an index of that time.
Some workers refer to the ETL as the action threshold to
emphasize the true meaning of the ETL. The relationship of the
ETL to the EIL and action times is shown in Figure 2.
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18. Figure 2: The relationship of the ETL to the EIL and time of
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19. The ETL is a complex value that depends on estimating
and predicting several difficult parameters.
The most significant of these include
1) the EIL variables (this is because the ETL is based on
2) pest and host phenology,
3) population growth and injury rates, and
4) time delays associated with the IPM tactics utilized.
Because of the uncertainties involved, particularly in pest
population growth rates, most ETLs are relatively crude;
they do not carry the same quantitative resolution as do
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20. Effects of Insect Pest on Crops
Insect pests have a significant effect on crop yields and
In crops with extensive pesticide use and cultivars with
resistance to insect and disease, losses have been estimated
between 20% and 30% of total yield.
Information on degree of damage resulting from insect
pressure in small-scale vegetable production is limited.
Lack of access to restricted use pesticides and cultivars
with limited resistance to insect and disease may result in
Improved crop protection strategies may lead to
significant increases in production efficiency.
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21. Due to difficulty in monitoring for pests threshold-
based approaches, applications of insecticides are
frequently conducted on a calendar schedule.
However, variability in pest populations leads to
inaccuracy and ineffectiveness of applications.
Improperly timed pesticide applications are both
expensive and may worsen problems by affecting
beneficial insect species without effectively
controlling the target pest.
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22. Regarding impacts of pesticides on the environment and
human health has led to development of integrated pest
management (IPM) programs.
These programs involve use of observation of pest
populations in the field to direct timing of pesticide
Central to the concept of IPM is use of an economic
threshold of a population level where application of a
pesticide is advisable.
IPM programs have been widely successful in reducing
pesticide use while increasing profitability of crop
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23. Diagnosis, monitoring, measuring, and forecasting
• The crop protection expert is often faced with
symptoms on plants caused by non-biological (abiotic)
causes including temperature, nutrient deficiencies
and sub-lethal effects of herbicides.
• The fundamental any crop protection strategy is to
identify the current pest(s) of concern or the potential
• This identification will lay the basis for any future
decisions to be made.
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24. Pest Monitoring
In most pest control situations, the area to be protected should be
monitored (checked or scouted) often.
Regular monitoring can answer several important questions:
• What kinds of pests are present?
• Are the numbers great enough to warrant control?
• When is the right time to begin control?
• Have the control efforts successfully reduced the number of pests?
Monitoring of insect, insect-like, and vertebrate pests usually is done
by trapping or by scouting.
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25. • Monitoring also can include checking environmental
conditions in the area that is being managed.
• Temperature and moisture levels, especially humidity, are
often important clues in predicting when a pest outbreak will
occur or will hit threshold levels.
• Monitoring is not necessary in situations where a pest is
continually present and the threshold is zero.
• For example, there is zero tolerance for the presence of
bacteria in operating rooms and other sterile areas of health
• In these situations, routine pest control measures are taken
to prevent pests from entering an area and to eradicate any
pests that may be present.
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26. Pest Forecasting
Forecast for pests is an important component of the IPM
• Early warnings and forecasts based on biophysical
methods provide lead time for managing impending pest
• consequently minimize crop loss, optimize pest control
and reduce the cost of cultivation.
• Prevailing and anticipated weather information can help
in crop planning and scheduling spray and farm operations
to maximize crop yields and returns.
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27. Outbreaks or epidemics of insect pests are usually caused
by one or more of the following:
1. Large-scale culture of a single crop.
2. Introduction of a pest into a favorable new area without its
3. Favorable weather conditions for rapid development and
multiplication of a pest; these same conditions may also be
unfavorable to natural enemies.
4. Use of insecticides which kill the natural enemies of a pest,
exert other effects favorable to a pest, or reduce the
competing species of a pest.
5. Use of poor cultural practices which encourage buildup of
6. Destruction of natural biotic communities which otherwise
provide regulation of insect population levels.
Causes of pest outbreak
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28. Favorable weather condition
Weather and climate has direct and indirect effect on
birth rate and death rate of insect pests.
The direct effect is: under favorable weather
conditions, birth rate is high and death rate low
The indirect is through the improvement in the growth
and condition of food plants.
If the good weather and climate favors the pest more
than the natural enemies, it will increase the rate of
growth of the pest population.
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29. Other Reason for Pest Outbreak due to human
i. Deforestation and bringing under cultivation
- Pest feeding on forest trees are forced to feed on
- Biomass/unit area more in forests than agricultural land
- Weather factors also altered
- Affects insect development
ii. Destruction of natural enemies
- Due to excess use of insecticides, natural enemies are
- This affects the natural control mechanism and pest
outbreak occurs, e.g. Synthetic pyrethroid insecticides kill
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30. iii. Intensive and Extensive cultivation
Monoculture (Intensive) leads to multiplication of pest’s
Extensive cultivation of susceptible variety in large area
- No competition for food
- multiplication increases e.g. Stem borers in rice and
iv. Introduction of new varieties and crops
• -Varieties with favorable physiological and morphological
factors cause multiplication of insects.
• e.g. Succulent, dwarf rice varieties favor leaf folder Combodia
cotton favors stem weevil and spotted bollworm Hybrid
sorghum (CSH 1), cumbu (HB1) favor shoot flies and gall
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31. v. Improved agronomic practices
Increased N fertilizer
- High leaf folder incidence on rice Closer planting
- BPH and leaf folder increases Granular insecticides
- Possess phytotoxic effect on rice
vi. Introduction of new pest in new environment
Pest multiplies due to absence of natural enemies in new
Apple wooly aphid Eriosoma lanigerum multiplied fast
due to absence of Aphelinus mali (Parasit)
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32. vii. Accidental introduction of pests from foreign
countries (through air/sea ports)
• e.g. a. Diamondback moth on cauliflower (Plutella
b. Potato tuber moth (Phthorimaea operculella )
c. Cottony cushion scale (Icerya purchase) on wattle tree
d. Wooly aphid - Eriosoma lanigerum on apple
e. Psyllid - Heteropsylla cubana on subabul
f. Spiraling whitefly - Adeyrodichus dispersus on most of
viii. Large scale storage of food grains Serve as
reservoir for stored grain pests Urbanisation - changes
ecological balance Rats found in under ground drainage
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33. Principles of Pest Control
Whenever you try to control a pest you will want to
achieve one of these three goals. or some combination
• prevention - keeping a pest from becoming a problem.
• suppression - reducing pest numbers or damage to an
acceptable level, and .
• eradication - destroying an entire pest population.
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34. Before making management decision
Entomologists and Pathologists should identify
the diseases or organisms encountered correctly.
Some insects will be immediately recognized as
insects but you may not be familiar with the order,
family and genus to which it belongs.
As you move from Class to Order to Family and
perhaps to Genus and Species you will notice that
choices may become more difficult.
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35. This is due to the details necessary to separate these
Once you have determined the Order, the next step is
to determine the Family within that order to which the
This may mean an increase in complexity for you, and
will usually require additional knowledge about
specific types of structures and the variation that exists
within these structures,
like antennae and its type, wings and types of
wings, mouth parts, presence and absence of
cornicles in aphids and the structures may
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36. In principle the identification of insects is the same as that of any
other animal. In practice it is more difficult, for two major
reasons. First, the massive number of species that occur means that
often very minor differences in structure must be used to
distinguish between forms, and second, the small size of most
insects frequently means that the identifying characters are not
There are various methods for identifying organisms:
The specimen may be sent to an expert
It may be compared with the specimens in a labeled collection
It may be compared with pictures or descriptions and
It may be identified by use of a key.
A tentative identification from a key should be confirmed by
comparing the specimen’s characters with the diagnosis or
description for the species.
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37. Insect and plant interaction
• Interactions between plants and their arthropod herbivores
dominate the terrestrial ecology of our planet.
• The survival of an estimated one million or more
phytophagous insect species depends on plants as a source of
• Plant-eating arthropods employ sophisticated feeding
strategies to obtain nutrients from all aboveground and
belowground plant parts.
• Insects and plants share ancient associations that date some
300 million years ago
• Evidence preserved in fossilized plant parts of insect damage
indicates a diversity of types of plant-feeding by insects
• which are presumed to have had different mouthparts
• Biting and Chewing(Nymph and adult of Orthoptera, larvae and adult
of coleoptera and larvae of lepidoptera)
• Siphoning (Lepidoptera-moth and bettery fly)
• Piercing and sucking (Hemiptera, Homoptera) aphid and bugs
• Rasping and sucking (Thysanoptera-Thrips and mites)
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38. Field sampling of insect pests
Sampling and monitoring (scouting) are fundamental
components of an IPM program
How to sample
Walk through the field/ orchard and count pests and
We need to reliably estimate the actual density (e.g. pests per
Estimate the density by sampling a only portion of the
We need to reliably estimate the actual density (e.g. pests per
Almost always interested in estimating mean density per
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39. Pest sampling and techniques
Sampling for pest and beneficial insects so important to
make cost-effective and environmentally sound pest
management decisions. Thus to:
Detect pest species that are present
Determine their population density
Determine how they are distributed in the field
Optimal timing of sampling depends upon the life history
and behavior patterns of the pest or beneficial insect and
also on the crop and environmental conditions.
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40. Methods of sampling
Random sampling involves selecting a number of samples
from a population such that every sample has an equal
chance of selection.
The simplest method for field studies
Stratified random sampling
Stratified random sampling differs from random sampling
only in the division of the population into different strata
from which random samples are then taken.
The strata are subdivisions of the samples based on
knowledge of the distribution of the population; for example,
insects may exhibit different preferences for particular
The strata reflect real differences in population levels while
each stratum consists of a more homogeneous subpopulation.
Systematic sampling involves taking samples at fixed
The size of the fixed interval and the reference or starting
point for the intervals are chosen, within defined limits
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41. Sampling technique depends upon:
The activity of insect pests such as: - Flying, mobile, diurnal
Feeding behaviour:-chewing (internal / external) or sucking
Part of the plant affected: whole plant, death of the plant,
Insect pest severity and incidence
Sweeping net: In this method, the density and height of crop,
number of sweeps required and type of insects involved in the
study are considered. Eg: 10 net sweeps are sufficient to
assess the general population of any insect.
Light trap: Quantitative assessment of population abundance
can be made. Eg: Jassids, gall midges, light attracted night
flying Lepidopterans Eg: Stem borers, army worm etc.
Phermon trap (meal bait).
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42. Suction trap: In this method, flying insects are trapped
by sucking air into trap with a suction apparatus operated
by fan or by means of motor. Eg: Beetles, weevils, jassids,
Sticky board: Suitable adhesive material (grease) pasted
on paper is used for collection of insects. Eg: Whiteflies,
jassids etc, eg. Yellow sticky trap for whitefly
Pitfall trap: are used to assess populations of insects and
other arthropods living on the ground surface.
Bait trap catch: Many materials are used for bait as they
stimulate food odours to attract insects. Eg: Fruit flies
(Malathion and jaggery), sorghum shoot flies (Fish
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43. Diagnosis of plant damage
Insect pests cause a particular type of damage to the plant parts often
characteristic to particular pests.
The pest mostly insect not present on the site of damage makes it difficult
to know the casual organism.
Sometimes, the symptoms of damage caused by insects may closely
resemble to pathogens or due to nutritional disorders.
So, practical experience makes familiar about the correct diagnosis on the
basis of visual symptoms of damage to take appropriate control measures.
Identify and classify the damage symptoms
Identify plant parts affected
Shoot damage:-Wilting, drooping of terminal plant part which later dries
up Eg: Shoot borers of cotton, castor, shoot fly of sorghum and black gram
Mines in leaf: Insect larval stages cause different types of mines infesting
between epidermal layers. Serpentine mines, thread like Eg: American
serpentine leaf miner, Eg: Citrus leaf miner,
Punctures on leaf: Leaves show punctures made by insects for feeding or
oviposition Eg: Bean flies
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44. Chapter Two: Major Economically Important of Insect Pest
Insect Pests of Cereal Crops
Insect pests teff (Eragrostis tef,)
Welo bush-cricket (Decticoides brevipennis Ragge),
Host Plants: The most important host plants are teff, flowers and
weeds are alternative host
Distribution- it is a major pest existing only in Ethiopia with its
distribution being recorded in the altitude range of 1550-2516 m in
Tigray, Walo, Gonder, Gojam and Shawa, but not in Walega
Damage: early instars of D. brevipennis are flower feeders,
slashing of weeds in the field margins before cereals have headed
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45. Management Options
Early sowing of the crops would enable them to
mature before the natural food sources of this potential
pest dry completely
As D. brevipennis has only one generation a year, one
well-timed application of insecticide can almost
eliminate it from an area, especially since migration is
seed dressing before sowing with 40% Aldrin WP at
the rate of 50 g/kg of seed is recommended.
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46. Red tef worm (Mentaxya ignicollis Walker)
Host Plat:- The most important host plants are teff,
Digitaria scalarum and Phalaris spp. were the
important alternate wild hosts of red tef worm.
Distribution:-was first reported as a pest of tef in
1970 south and west of Addis Abeba on black clay
Since then, losses from red tef worm were estimated
to be l0-30% in five regions of Ethiopia.
Repeated crop losses have been observed in Becho
area of Shewa
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47. Management Options
• Cypermethrin, 25%EC. (187.5 g a.i./ha, 750 ml/ha) or
• Fenitrothion, 50% EC (625.0 g a.i./ha, 1.25 ml/ha).
• Spraying should be done when, on the average; 25
larvae/m2 of red tef worm are counted.
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48. Insect pests of Wheat
Russian Wheat Aphid (Homoptera: Aphididae)
Host Plants: The most important host plants are wheat and
barley, but at cool season grasses are alternative host.
Distribution- A serious pest in the highlands at 2400 m
above sea level and higher in Ethiopia.
Damage: Nymphs and adults feed on plant phloem with
a piercing-sucking stylet.
The insect prefer to feed on foliage and grain spikes of
actively growing plants.
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49. While feeding, these aphids can transmit a toxin that
causes discoloration and distortion of the plant.
Heavily infested leaves will have longitudinal white,
purple or yellow streaks.
The leaves curl inwards and the plants remain stunted.
This species is known to be a vector of virus diseases
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51. Management Options
Weekly scouting and timely insecticide applications can
protect grain yields loss.
Biological control from parasitic wasps, predators and
fungal pathogens are abundant.
Remove volunteer grain and wheat grasses to eliminate
refuge between spring and fall crops.
Select certified varieties that are well suited for the
Use aphid resistant wheat and barley cultivars
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52. Barley Shootfly
• Diptera: Anthomyiidae
• Main host: Barley
• Alternative hosts- Maize, Wheat, Bulrush millet, Teff,
The larva feeds on the stem of the central shoot.
The central shoot turns brown, dies, and may be easily
pulled out of the plant.
This typical shoot borer damage is called a "dead heart".
One larvae may destroy three or four shoots.
In years of high infestation this pest can cause 40-50%
reduction or total failure of the crop if rainfall is low
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53. Management suggestions:
Cultural practices such as rotation that avoids cereal
followed by cereal, and fertilization to favor tillering are
the only means of reducing damage by some Shoot Fly
In some conditions a delay of planting date helps.
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54. Maize/Sorghum Stem Borers Busseola fusca
• Main hosts-Maize, and Sorghum
• Alternative hosts- Sugarcane, Many species of grasses and cereals
• Geographical Distribution: Busseola fusca is a common pest in
East Africa it occurs at altitudes of 1000 to over 2700 m
• Symptoms: Young plants show small holes and 'window-panes' in
the leaf whorls where tissues have been eaten away.
• Damage is caused by the caterpillars, which first feed on young
leaves, but then enter into the stems.
• During the early stage of crop growth, the caterpillars may kill the
growing points of the plant, causing what is known as dead-heart
(the youngest leaves can be easily pulled off).
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55. • At a later stage of growth, they make extensive tunnels
inside the stem. This disrupts the flow of nutrients to the
• Tunnelling weakens the stem so that it breaks and falls
• In older plants the first generation caterpillars bore in the
main stem but later some of the second generation bore
into the maize cobs.
• Caterpillars also tunnel into the peduncles of sorghum
and millet inflorescences, and may seriously affect grain
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58. Stem borer damage
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59. Because maize plants don't produce tillers, they are
less able to tolerate stem borer attack than sorghum and
pearl millet plants and the effect on grain yields is
severity of infestation and damage strongly depend on
the cropping system and soil fertility, which affects the
nutritional status of the plant.
Stem borer damage is aggravated by the poor nutritional
status of the plant.
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60. Damage caused by stemborers can average 20 to 40%,
which means between 2 to 4 bags of maize are lost out of
every 10 that could be harvested.
Grains damaged by pests such as stemborers become
susceptible to infection by mouldy fungi such as
Aspergillus which produce aflatoxin, a toxic by-product
extremely poisonous to people and which can lead to
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62. Spotted Stem borer, Chilo partellus (Lepidoptera: Crambidae)
• Origin and Distribution: it is a pest of maize and
• It occurs in low to mid-altitude areas (1230 m altitude and
• Damage Symptoms: Larvae (caterpillars) eat through
leaves when young and as they grow older, eventually
bore into the stem causing it to break (lodge) or die
resulting in a condition called 'dead heart'.
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• Cultural practices
• Scouting and early control is essential for effective
management of stem borers. Check the crop regularly.
First signs of stalk borer attack are small holes or
'window panes' in straight lines across the newest leaves
of maize or sorghum.
• Field sanitation:
• Destroy crop residues. This is important to kill the pupae
left in old stems and stubble and to prevent carry-over
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64. • Improvement of soil fertility:
• Maintaining soil fertility or practices that increase
nitrogen use efficiency in maize production are
important for management of the African stalk borer.
• Crop rotation:
• Maize-legume rotation sequences improve the supply
of nitrogen in the soil and the nutritional status of
maize, which compared to maize-maize sequences.
• This influences the maize susceptibility to pests and
• Intercropping and habitat management:
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65. Sorghum Chafer (Pachnoda interrupta)
Main hosts-Sorghum, Pearl millet, Maize
Alternative hosts-Flowers of cotton, Citrus spp, and few other plants
Distribution-Especially serious in the North of Ethiopia at altitudes
below 2000 m above sea level.
Damage-The adult beetles eat the grains in the milky stage.
Sorghum midge Contarinia sorghicola (Cecidomyiidae:
• Distribution: It has a worldwide distribution and is considered to
be one of the important pests of sorghum.
• Nature of damage: The maggots feed on the developing grains and
cause the developing grains to shrivel and severe infestation has a
significant effect on the overall production of grains. The loss varies
from 20 - 50 %.
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67. Cutworms (Lepidoptera: Noctuidae)
Common cutworm (Agrotis segetum) and Tobacco cutworm/Black cut worm
Cutworms attack cultivated plants belonging to more than 15 families. Common
host plants include okra, cabbage, cauliflower, rutabaga, bell pepper, tomato,
potato, maize and cotton.
External feeding on leaves by young caterpillars results in the presence of very
tiny round window panes. Feeding on leaves, stalks and stems results in falling
leaves, small holes in the stems or cut stems respectively.
Feeding on tubers and roots results in a variety of holes, ranging from small and
superficial to very large deep ones.
Feeding by medium to large caterpillars is easier to recognise because whole
leaves may fall off the plant after being cut through at the base of the stalk.
Damage is far more severe under very dry conditions and occurs deeper below the
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68. Control options
Ploughing exposes caterpillars to predators and to
desiccation by the sun.
Fields should be prepared and vegetation and weeds
destroyed 10 to 14 days before planting the crop in the
Delaying transplanting slightly until the stems are too
wide for the cutworm to encircle and/or too hard for it
to cut may reduce cutworm damage..
Flooding of the field for a few days before sowing or
transplanting can help kill cutworm caterpillars in the
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