use full Guide for students, agriculture experts, and grower's principles of any pest management in an effective way in order to boost crop production by lowering the pest population below the economic injury level

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Introduction
• Principles of Pest Management
– Pest definitions, kinds and outbreaks
Definition of pests: -
❖ Pest is a general term used to describe any organism that is
harmful to our health and properties including crop and
livestock.
❖ The term, in its broader sense also includes
microorganisms, parasites, and weeds.
❖ Insects reached a pest status when they cause more than
5% yield loss.
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Classification of pests.
• For proper study and understanding pest might be
classified based on several criteria.
❖ Classification based on morphological difference.
1. Weeds and parasitic plants: - any plants grown in
unwanted time and place.
❖ Weeds are unwanted plants in the field that compete with
the crop plants for water, nutrient and light.
❖ Many parasitic plants depend on their host tree for their
growth and reproduction.
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2. Invertebrate pests: animals without backbones.
• This includes insects and their relatives, nematodes, snails
and slugs, mites, etc.
a. Insect pests: an insect that multiplies rapidly and builds
up a huge population causing economic loss to crops and
health hazards to animals.
➢ Insects damage crops by making injury and being vector
of plant diseases.
➢ Insects have mouthparts modified for different feeding
habits
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• The primitive forms have the biting-chewing
type like in grasshopper but other forms are
modifications of biting-chewing type.
• Based on feeding mechanisms insects can be:
Defoliators: these have biting-chewing mouth
parent and feed on the foliage (leaves). E.g.
Grasshopper, beetles, and caterpillars.
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Borers: these also have strong mandibulate
mouthparts that make holes in to the plant parts like
stem, twigs, roots, fruits and seeds.
➢ Based on the plant part damaged these insects are
known as trunk borers, twig borers, stem borers,
fruit borers, shoot borers, seed borers, etc.
Suckers: these insects have piercing and sucking
type of mouthparts. E.g. stink bugs, aphids, hoppers.
Raspers: these are tiny insects, which scrape the top
layer of tissues and suck the sap.
Thrips and mites cause this kind of damage.
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Gall makers: galls are the result of abnormal growth
of plants cells because of certain stimulation by
insects.
• The stimulation may be due to secretion of certain
chemicals while feeding or laying eggs.
• The insect get surrounded by the plant tissue and
feeds inside on these tissues.
b. Mite pests: mites are not actually insects, but tiny
insect like creatures belong to the related class
Arachnida, which also includes spiders, scorpions,
and ticks.
• Mites cause considerable injury to plants and
animals.
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• The scientific discipline devoted to the study of ticks
and mites is called acarology. While insects have
three body regions (head, thorax and abdomen), mites
have only two body regions (head and abdomen).
• Insects have generally three pairs of legs, but adult
mites possess four pairs.
C. Mollusks: these include slugs and snails.
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3. Vertebrate pests: animals with backbones are called
vertebrates.
✓ It includes fish, amphibians, reptiles, birds and mammals.
✓ Animals such as wild pig, monkey, bear, elephant, deer,
the rodents and birds are some example of vertebrate
pests.
4. Microorganisms (pathogens)
• Some microorganisms including bacteria, fungi,
viruses and nematodes cause diseases in plants.
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Microorganisms that cause diseases in plants are also
known as plant pathogens or phyto-pathogens.
Ralstonia solanacearum (Pseudomonassolanacearum)
is a plant pathogenic bacterium that causes tomato plants
to wilt.
Similarly, Xanthomonas campestris causes bacterial leaf
spots in sesame, cabbage, etc.
Phytophtora infestant is a plant parasitic fungus causing
late blight disease in potato.
Many viruses cause disease symptoms such as mosaic,
yellowing, leaf curls, puckering, bunchy tops, etc.
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• Plant parasitic nematodes are usually too small to be
seen without a hand lens or a dissection microscope.
• Because of their tiny size, they remained unstudied
for a very long time.
• Several crop diseases are caused by nematodes.
• Root and seed galls, stubby roots, yellowing, etc are
few examples.
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❖ Classification based on attack
• Generalist pest: is pest that can attack wide ranges of
hosts. E.g. most weeds and insects.
• Specific pest: is pest that attack specific hosts. E.g.
most diseases and some insects
• Opportunistic (potential) pests: they are not
actually a pest, but occasionally become a pest. Few
pathogens and insects like locust only occur when
they get right environment.
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❖ Classification based on importance
✓ Many insects feed on our crops, but not all are pests.
✓ To be designated as pest, an insect must be responsible
for an economic yield loss of at least 5%.
✓ Insects are categorized in to major and minor pests
based on the percentage yield loss they cause.
• Major pests: major pests are those that cause damage
over 10%.
• Minor pests: are those that cause damage 5% to 10%.
Damages below 5% are tolerable and often negligible.
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❖ Classification based on origin:
• Pests can be disseminated from one place to other
places.
• In a given habituate of pests, some of them might be
those present over generation in a given location
while other are newly introduced in to new areas.
• Exotic pests (Aliace): pests introduce to new
areas from its center of origin.
• Indigenous pest: pests that regularly observed
in a given area for very long time.
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❖ Classification based on spread
• Invasive pest: pest that can increase its population and spread with in
short time.
• Contained pest: pests that regularly present with in localities.
• Regular pest: a pest that occurs every crop season and causes
yield losses.
• Occasional pest: a pest that is irregular, but occasionally
causes problems.
✓ It is a pest that occurs here and there in an irregular or random
pattern.
✓ This pest appears only when conditions favors their growth.
• Seasonal pest: pests occur in specific season. Winter or
summer, etc.
• Sporadic pest: a pest that could become highly noxious if
allowed to establish.
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• Why we study pests?
• Pests reduce quantity and quality (loss in color, odor,
marketable value, etc) of plant produce.
• Pests limit kinds of plants and industries in the area.
• They cause financial losses (cost of management, labor,
chemicals, materials, etc).
Out breaks of pests (pest epidemic)
• When pests spread to and affect many individuals in a
population over relatively large area with in relatively
short period of time it is called an epidemic or pest
outbreak.
• The study of epidemics factor that influence them is called
epidemiology.
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• Epidemiology then concerned with population of
pathogens and host plants as they occur in the evolving
environment.
• With exception of trees, the damage or loss of one or
few plants is usually considered insignificant.
• Hence epidemiology concerns not for individual, but for
population of plants.
• Thus pest epidemiology concerned with host character,
environmental conditions, pest character and human
factors.
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a) Elements of pest epidemics/outbreaks
• Pest epidemics develop as a result of the timely
combination of some elements that result in pest attacks.
➢ The chance of epidemic increase when
i. Susceptible host or host range
ii. Serious pest
iii. Favorable environmental conditions
iv. Time of occurrence and infection
v. Human practice: it is major factor leading to pest
outbreaks
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i. Host factor
• Host (plant) factor plays an important role in pest
epidemics.
• This includes:
✓ Level of genetic resistance or susceptibility of the host:
in the presence of serious pest and favorable environment,
susceptible host favors development of epidemics.
✓ Degree of genetic uniformity of host plants: for reasons
of genetic uniformity, epidemic development is generally
high in vegetative propagated crops, medium in self
pollinated crops and low in cross pollinated crops.
• This might be one reason why epidemics are developed
slowly in nature, where plants of various genetic make ups
are intermingled.
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✓ Types of host: pasts are more common in annual crops
than perennials.
• Annual plants are more succulent and bear soft leaves
which are very prone to pest outbreaks.
• It is also common in leaf than stem.
✓ Age of host plant: different pest attack plant at different
plant age.
• Some pests start to attack from seedling stage while
others may start at vegetative stage or productive stage.
• Plants might have different level of resistance at different
age.
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• The change of resistance with age is known’s
ontogenic resistance.
• Most insects attack plants during early stages, few
attack at vegetative and flower stages.
• Weeds attack or compete plants at any stage.
Adult resistance: plant susceptible at early stage and
become resistant at young stage. E.g. bacterial blights,
viral infections, rust, systemic smuts, damping off, root
knot, powdery mildews, etc.
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Old resistance: plants are resisting during growth
and early adult period but susceptible near
ripening. E.g. most fruit diseases and post harvest
diseases.
Plant might be resistant at juvenile stage and become
susceptible at young stage followed by resistant latter in
their growth. E.g. viral and rust infections.
For some of the diseases plant might be susceptible
during juvenile stage followed by relatively resistant at
adult stage and then susceptible during maturity. E.g.
tomato late blight, potato late blight.
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ii. Pest factor
• Pest nature: ability to attack plants.
✓ This includes aggressiveness of the pests.
• Quantity of pests: this includes amounts of inoculums
for pathogens, number of insects and weeds.
• Types of reproduction: some pests produce small
offspring while some others produce many offspring.
• Pest ecology: most pests might thrive in wider
ranges of habitat, soil and climatic conditions or
adapt only to narrow/specific conditions.
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• Mode of spread: depending on their nature (seed,
spore, egg, mobility, etc) pest might be spread by air,
soil, vector, planting materials, animals, human being,
etc. the chance of outbreak of wind and seed born
pathogens are very great.
• Ability to compete with enemies and other
organisms: the more the pests are competent enough
to survive the effects of enemy the more chance they
become epidemic.
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iii. Time factor: time factor involved to affect all other
epidemic factors (host, environment and pests).
✓ For instance time of rainfall, duration of rainy season, time
of sunshine, time of planting of crops, time of maturity,
time of occurrence of insect pests, time of development of
vectors, time of infection, time of symptom development,
etc are among time factors determining pest epidemics.
iv. Environmental factors: even if pests get right host this
does not always grantee that they attack the plant. The
environment may affect availability, growth stage,
succulence, genetic susceptibility of host plants.
✓ It may also affect survival, vigor, rate of reproduction,
spread and growth of pests.
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• The most important environmental factors affect
developments of pests are temperature and moisture.
• Others like soil type, RH, sunlight, leaf wetness etc. can
also be factors.
v. Human factors: human has direct or indirect effect on
pest outbreaks.
• Site selection and field preparation: selection of safe
heaven for the enemy always turns down the soldier!
For example selection of logged soil always aggravated
bacterial blight of sesame crops.
• Selection of virgin soil usually minimizes risk of pests.
Most disease needs foliar water for development.
• In this case use of irrigation tends to be appropriate.
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• Selection of preparative material: bad starting brings worst ends!
Starting with infected planting materials might introduce pests in
to new areas and can bring more infection and spread.
• Free preparative material reduces the risk of epidemic.
• Cultural practices: monoculture, improper use of fertilizers and
irrigation (time, dose and method), crop density, planting time and
methods, pesticide application, sanitation, tillage practices, etc are
also human factors determining pest outbreaks.
• Pest control measures: different control methods might be
practiced by farmers.
• This might be biological, cultural, physical, chemical, methods,
etc.
• If they are not practiced properly and safely they might bring pest
outbreaks.
• Frequent use of pesticides might lead pest resistance which no
longer minimized by pesticide application.
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1.2 Types of insect pests damage
• Tissue damage: it is the damage on any part of the
plant (leaf, stem, etc.) and caused by insects with
chewing and biting mouth types.
• Sap sacking (extracting): the juice and liquid
materials are extracted from plant parts by insects
with sucking and piercing mouth types.
• Toxic saliva: materials being toxic and harsh to plants
are transmitted to plant parts. E.g. true plant bugs.
• Disease transmission: some insects transmit diseases
to plants from other plants in addition to feeding the
plant parts.
• Crop (yield) loss: the final result by insect pest
infestation can lead to loss.
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1.3 Pest population and concepts of injury level
• It is always desirable for growers to have flexibility
in timing of decision of management measures
especially with those related to pesticide application.
• The presence of single insect or very limited disease
does not mean that growers should go for application
of pesticides.
• The growers must know what amount of pests it must
still tolerate before application.
• The economics of damage to plants and costs applied
to protect the damage must be meaningful.
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• By using economic injury levels and economic
thresholds, an educated decision can be made, based on
expected outcomes.
• The original definition of the economic threshold was
coined by Stern et al. (1959) as ‘the density at which
control measures should be determined to prevent an
increasing pest population from reaching the economic
injury level’.
• The ‘economic injury’ level (EIL; sometimes referred to
as the ‘damage threshold’) is the ‘lowest population
density that will cause economic damage’ and ‘economic
damage’ being the ‘amount of injury which will justify
the cost of artificial control measures’.
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• What was meant by ‘will justify’ was not made
entirely clear but it has subsequently been accepted to
mean ‘the density of the pest at which the loss
through damage just exceeds the cost of control’.
Generally;
➢ The economic injury (EIL)/Damage threshold
level: is the lowest population density at which the
value of actual or potential damage caused by insects
equals the cost of controlling the population. E.g.
start control when two larvae appear on corn.
• Infestation higher than this number can cause
economic loss.
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➢ Economic threshold (ETL)/Action threshold level:
is a slightly smaller number and represents the pest
density at which control measures should be initiated
to prevent the pests from exceeding the economic
injury level.
• Control started at the point when highest pest infection
of infestation level does not decrease economic level.
• One of the greatest values of the economic threshold
concept is monitoring the buildup of potentially
damaging pest populations reaching a control or
management decision before econonomic yield loss
occur.
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• Sometimes pests especially diseases reach their
epidemic level at latter stage of the crops.
• Application of pesticides during this time might not
increase yield except increasing our cost.
• At this time, the concept of economic threshold helps
in taking decision whether to apply pesticides or not.
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Chapter 2
MANAGEMENT METHODS OF PESTS
2.1 Concept of pest management and pest control
• The ultimate goal of any study related to pest is to keep
human and plant welfares.
• The study should not be something for nothing.
• After knowing classes, bionomics, ecology and other
characteristics of pest species we start to think to
manage the damage pests pose or how to utilize them
for our benefit
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• Literally some people use the term pest control rather
than pest management.
• But there are conflicts of interests and ideas between
both terms.
• It is impossible to overcome everything.
• It is also obscuring the natural right to live.
• The word control seems application of forces and
power.
• The word management literally has effects of
negotiation and living together peacefully.
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• Pest control: any measure or thing that is capable of
making life hard for pests, or that kills, repels, or
interferes with their feeding, reproduction or spread.
• Pest management: pest control strategy based on the
understanding of pest population dynamics and its biotic
potential and environmental resistance.
• It means to maintain the pest population below those
causing the economic injury level.
• Pest management includes any events before the pest
arrives to the host and control after arrival, while pest
control is only direct protection after pest arrival or
establishment.
• There are two ways in which pests are controlled and
managed.
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• Natural pest control: the control goes on in nature
without the intervention of man.
• It is the collective action of environmental factors,
physical and biotic, that maintain population of insects
within certain upper and lower limits over a period of
time.
• The important factors of natural control are
climatological factors, natural enemies, availability of
food and space, diseases, etc.
• Applied pest control: it includes the whole range of
practices developed or modified by man, which
becomes necessary when natural control factors fail.
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2.2 Cultural pest control
• Cultural control includes the long-established
agricultural practices that make habitats less suitable for
pests.
• The methods used may directly affect a pest, stimulate
an increase in density of a pest’s natural enemies, or
make the organisms on which a pest feeds more tolerant
of attack.
• An essential prerequisite for effective cultural control is
detailed knowledge of a pest’s life history so that its
most susceptible stages can be determined.
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• For crops, important agricultural practices include
1. crop rotation to prevent buildup of pest populations
2. planting or harvesting out of phase with a pest’s
injurious stage(s), which is especially important against
species that have a limited period of infestation or for
plants with a short period of susceptibility
3. use of trap crops on which a pest will concentrate,
making its subsequent destruction easy
4. soil preparation, so as to bury or expose a pest, or
increase the crop’s strength so that it can more easily
tolerate a pest
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Cont’….
5. clean culture, the removal, destruction, or ploughing
under of crop remains, in or under which pests may
hibernate; and
6. crop diversity, that is, reversal of the current practice of
monoculture (growing a single crop over a wide area).
• Studies have shown that damage to mixed crops or
diverse natural vegetation is much less than that done to
plants in monoculture.
• In mixed crops pests may experience greater difficulty in
locating their host plant, while the occurrence of diversity
may improve the resources available for parasitoids and
predators of the pest.
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2.3 Physical and mechanical pest control
• Physical control involves manipulation of temperature,
humidity and the use of radiant energy, while mechanical
control involves employing manual devices and machines.
• E.g. picking, shaking, beating of branches, banding, trench
digging, trapping (light trapping, food preference (baits),
sticky trap, window pain traps, vacuum trap, pheromone
trap, and sound trap), flooding, etc.
• Physical methods are particularly useful for destroying
stored grain pests. E.g. Low temperature (<4oC) and
exposure to heat (51.5-54.5oC) is used to disinfest maize
grains.
• Solar heat treatment and hot water treatment are more
economic physical methods.
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2.4. Regulatory control methods
• Also known as legal control, regulatory control is based
primarily on the old proverb “Prevention is better [in this
instance, cheaper] than cure.”
• Legal control is the performance of legislation to prevent
or control damage by insects.
• It includes, therefore, establishment of quarantine stations
at major ports of entry into an area.
• Usually the stations are located at international borders,
though in some instances domestic quarantines are
necessary.
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Cont’….
• At quarantine stations people and goods are inspected to
prevent the accidental introduction of potential insect
pests and plant and animal diseases.
• As an addition to quarantine, many countries (or areas
within countries) have legislation that requires
international or interstate shipments of animals or plants,
or their products, to be certified as disease or insect free
by qualified personnel prior to shipment.
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Cont’….
• Also part of legal control is the setting up of surveillance
systems for monitoring the insect population in a given
area so that, should an outbreak occur, it can be dealt with
before it has a chance to spread.
• Such surveillance is an important duty of crop
protectionist, in cooperation with local agriculture
representatives and crop and livestock producers.
• Another aspect of legal control, and one that has become
increasingly important, is the licensing of insecticides and
the establishment of;
• 1) regulations regarding their use and
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Cont’….
2) monitoring systems to assess their total impact on the
environment.
• For example, in the United States the Environmental
Protection Agency is responsible for assessing the
effectiveness of pesticides, as well as their possible
hazardous effects on humans, wildlife, and other
organisms, including bees, other pollinating species,
and beneficial parasitoids
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2.5 Botanical control
• Active products of plant origin being less persistent in
environment and safe to mammals and non-target
organisms have become the focus of attention today.
• Botanical pesticides are readily available in many places;
often cheaper than their synthetic counterparts are and
their crude extracts are easy to prepare even by farmers.
• They are also less likely or slower to result in the
development of resistance or resurgence in pests. There
are some well-known sources of botanical pesticides like
neem, tobacco, pyrethrum, melia, etc.
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2.6 Biological Control of Pests
• Biological control is the regulation of pest populations
by natural enemies.
• For insect pests, parasitoids, predaceous insects, and
micro organisms are the major control agents.
• Its main disadvantages are its slowness of effect.
• Other problems identified from some biological control
projects include extinction (of both the original pest and
non-pest species), enhancement of the target pest
population as a result of secondary outbreaks, and
change to pest status for the original control agent.
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• Both target and non-target animals (including many
insects) may become extinct as a result of the direct or
indirect effects of biological control agents.
• In other situations, introduction of an exotic control
agent may lead to displacement of already present natural
agents, without significant gains in pest control.
• In some cases, an introduced control agent has itself
become a pest as a result of changing its diet to a useful
plant either in preference to the weed or following the
termination of the weed for whose control it was
imported.
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❖ Microbial control (the use of pathogenic bacteria, viruses,
nematodes, fungi, and protozoa) is playing an increasingly
important role in the control of insect pests.
• Strategies for the use of micro organismal agents include
introduction, augmentation, and conservation.
• The advantages of microbial control (safety to humans and
wildlife, specificity, bio degradability, and low registration
costs) have been some what offset by the slow-acting
nature, low powers of dispersal, and mass-production
problems of the agents.
• Genetic engineering should remove some of these
disadvantages.
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• Biocontrol involve three principal ways.
I. Collection of natural enemies and releasing where
they are not.
II. Rearing and releasing them whenever needed.
III. Importing and releasing whenever needed.
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2.7. Chemical control
• The use of chemicals either to kill or to repel insect
pests is the oldest method of pest control.
• Chemical control traditionally has been the use of
naturally occurring or synthetic chemicals to kill
pests.
• It has been the major method of pest control for
about long years, but has created three serious
problems:
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1) a great increase in the resistance of pests to the
chemicals
2) the death of many beneficial insects as a result of the
chemicals’ non-specific activity, and
3) pollution of the environment.
• For the last decades pest control has been achieved
almost exclusively by use of pesticides for the reasons of
➢ Pesticides provide the easiest, quickest way of reducing
pest population.
➢ The broad spectrum nature of early pesticides protected
crops from variety of pest species and a single
application was often sufficient for control.
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Cont’….
• Development of crop technology and application equipments
made it economically feasible to apply pesticides; that is cost
return benefits for pesticides were maximized.
2.8 IPM
• Integrated pest management (IPM) is a combination of
methods for reducing and maintaining pest populations
below the economic injury threshold.
• There are three phases in the development of an IPM
strategy: problem definition, research, and
implementation, of which the first is the most important.
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• To be most effective, IPM requires the input of as much
information as possible, not only about the agro
ecosystem, but also about the socioeconomic framework
of the farming system in which the pest problem occurs.
• Thus, the collaboration of experts from a wide range of
disciplines is necessary.
• If conducted properly, IPM leads to considerable
financial saving and a great improvement in
environmental quality.
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Cont’….
• The IPM approach can be applied to both agricultural
and non-agricultural settings, such as the home, garden,
and workplace.
• IPM takes advantage of all appropriate pest
management options including, but not limited to, the
judicious use of pesticides.
• In contrast, organic food production applies many of
the same concepts as IPM but limits the use of
pesticides to those that are produced from natural
sources, as opposed to synthetic chemicals.
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How do IPM programs work?
• IPM is not a single pest control method but, rather, a series of
pest management evaluations, decisions and controls.
• In practicing IPM, growers who are aware of the potential for
pest infestation follow a four-tiered approach.
➢ The four steps include:
Set Action Thresholds
➢ Before taking any pest control action, IPM first sets an action
threshold, a point at which pest populations or environmental
conditions indicate that pest control action must be taken.
➢ Sighting a single pest does not always mean control is
needed.
➢ The level at which pests will either become an economic
threat is critical to guide future pest control decisions.
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Cont’….
• Monitor and Identify Pests
➢ Not all insects, weeds, and other living organisms
require control.
➢ Many organisms are innocuous, and some are even
beneficial.
➢ IPM programs work to monitor for pests and identify
them accurately, so that appropriate control decisions can
be made in conjunction with action thresholds.
➢ This monitoring and identification removes the
possibility that pesticides will be used when they are not
really needed or that the wrong kind of pesticide will be
used.
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• Prevention
➢ As a first line of pest control, IPM programs work to
manage the crop, lawn, or indoor space to prevent
pests from becoming a threat.
➢ In an agricultural crop, this may mean using cultural
methods, such as rotating between different crops,
selecting pest-resistant varieties, and planting pest-
free rootstock.
➢ These control methods can be very effective and cost-
efficient and present little to no risk to people or the
environment.
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Cont’…..
Control
• Once monitoring, identification, and action thresholds
indicate that pest control is required, and preventive
methods are no longer effective or available, IPM
programs then evaluate the proper control method both
for effectiveness and risk.
• Effective, less risky pest controls are chosen first,
including highly targeted chemicals, such as pheromones
to disrupt pest mating, or mechanical control, such as
trapping or weeding.
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Cont’….
• If further monitoring, identifications and action thresholds
indicate that less risky controls are not working, then
additional pest control methods would be employed, such as
targeted spraying of pesticides.
• Broadcast spraying of non-specific pesticides is a last resort.
The goals of IPM
• The goals of IPM are:
✓ Improved control: it will provide more effective pest control
to maintain and sometimes improve crop quality.
• E.g. by implementing alternatives to strict dependence on
pesticides, IPM makes use of a balanced approach relying for
example on practices, natural enemies already occurring in
the environment.
2/7/2021 59
Cont’…..
✓Pesticide management: IPM will supply more
efficient and sensible approach to pesticide, thus
increasing their effectiveness and useful life span
and decreasing possible adverse effects.
✓Economic crop protection: it will control pest
populations economically.
• E.g. simply by treating as needed instead of merely
by calendar.
• It can offer reduced protection cost by reducing
amount and number of application.
✓Reduction of potential hazards: IPM will better
safeguard human health and environment from
possible side effects associated with pesticides.
2/7/2021 60

16. 2/7/2021
16
Chapter 3
MAJOR SEEDLING DISEASE and INSECT PESTS
1.1. Major Seedling Disease
Damping off (Pythium spp.)
✓ seedlings occur worldwide in valleys and forest soils, in
tropical and temperate climates, and in every greenhouse.
✓ rotting and collapse of seedlings at soil level or
prevention of seedling emergence (e.g. damping-off of
vegetables and tobacco)
✓ It is destruction of seedlings near the soil line, resulting in
the seedlings falling over on the ground
✓ In all cases, however, the greatest damage is done to the
seed and seedling roots during germination either before
or after emergence.
2/7/2021 61
Cont’….
✓ Losses vary considerably with soil moisture, temperature,
and other factors.
✓ Quite frequently, seedlings in seedbeds are completely
destroyed by damping-off or they die soon after they are
transplanted.
✓ In many instances, poor germination of seeds or poor
emergence of seedlings is the result of damping-off
infections in the pre-emergence stage.
✓ Older plants are seldom killed when infected with the
damping-off pathogen, but they develop root and stem
lesions and root rots, their growth may be retarded
considerably, and their yields may be reduced drastically
2/7/2021 62
Cont’…..
• Some species of the damping-off oomycete also attack
the fleshy organs of plants, which rot in the field or in
storage.
• Pythium debaryanum, P. ultimum, and P.
aphanidermatum cause damping-off of vegetables and
fruit trees.
• Pythium arrhenomanes, P. graminicola, and P.
tardicrescens cause root rot in cereals.
2/7/2021 63
Symptoms of Damping off
• When seeds of susceptible plants are planted in
infested soils and are attacked by the damping-off
fungi, they fail to germinate, become soft and
mushy, and then turn brown, shrivel, and finally
disintegrate (Fig. 1- A).
• Young seedlings can be attacked before emergence at any
point on the plant, from which the infection spreads
rapidly, the invaded cells collapse, and the seedling is
overrun by the oomycete and dies (pre-emergence
damping-off).
2/7/2021 64

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17
Cont’…..
• Seedlings that have already emerged are
usually attacked at the roots and
sometimes in the stems at or below the
soil line.
• The invaded areas become water soaked
and discolored and they soon collapse
(Figs. 1- B and C).
2/7/2021 65
Cont’…..
A B C
Figure 1 (A) Pythium seed rot. (B) One healthy bean seedling
and several seeds and seedlings infected with Pythium. (C)
Damping off of cucumber seedlings caused by Pythium sp.
2/7/2021 66
Cont’…...
• The basal part of the seedling stem becomes softer
and much thinner than the un invaded parts above it;
as a result, the seedling falls over on the soil.
• The fungus continues to invade the fallen seedling,
which quickly withers and dies (post-emergence
damping-off).
• In cereals and turf grasses, the pathogen causes
“Pythium blight,” i.e., it invades and kills the roots
and whole seedlings and even young plants, causing
the appearance of numerous empty patches on the
lawn or field
2/7/2021 67
Cont’…..
• Several species of Pythium cause pre- and post-
emergence damping-off.
• Certain other oomycetes and fungi, however, such as
Phytophthora, Rhizoctonia, and Fusarium, often cause
symptoms quite similar to those described earlier.
• Several more fungi, and even some bacteria, when
carried in or on the seed, also cause damping-off and
kill seedlings.
• Pythium produces a white, rapidly growing mycelium.
2/7/2021 68

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18
Cont’….
• The mycelium gives rise to sporangia, which
germinate directly by producing one to several germ
tubes or by producing a short hypha at the end of
which forms a balloon-like secondary sporangium
called a vesicle (Figs.2 and 3).
• In the vesicle, 100 or more zoospores are produced,
which, when released, swarm about for a few
minutes, round off to form a cyst, and then
germinate by producing a germ tube.
• The germ tube usually penetrates the host tissue and
starts a new infection, but sometimes it produces
another vesicle in which several secondary
zoospores are formed, and this may be repeated.
2/7/2021 69
Cont’…..
A B
2/7/2021 70
Cont’…
• The mycelium also gives rise to spherical oogonia and
club-shaped antheridia ((Figs. 2- A and B).
• The antheridium produces a fertilization tube, which
enters the oogonium; nuclei of the antheridium move
through the tube toward the nuclei of the oogonium,
unite with them, and form the zygote.
• The fertilized oogonium produces a thick wall and is
then called an oospore (Fig. 2-B).
• Oospores are resistant to adverse temperatures and
moisture and serve as the survival and resting stage of
the fungus.
2/7/2021 71
Disease cycle
• The fungus survives in the soil as oospores and
chlamydospores.
• The primary infection is from the soil-borne oospores
and secondary spread through sporangia and zoospores
transmitted by wind and irrigation water.
Favorable Conditions
• Overcrowding of seedlings, ill drained nursery beds,
heavy shade in nursery, high atmospheric humidity (90-
100 %), high soil moisture, low temperature (below
240C) and low soil temperature of about 200C.
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19. 2/7/2021
19
• Figure 3. Disease cycle of damping-off and seed decay caused by
pythium sp.
2/7/2021 73
Cont’…..
• Management: Pythium diseases in the greenhouse can
be controlled through the use of soil sterilized or
pasteurized by steam or dry heat and through the use of
chemically treated seed.
• Greenhouse benches and containers must also be
sterilized or treated with an appropriate chemical
solution.
• Raised seed beds of 15-45 cm height should be formed.
• Avoid overcrowding of seedlings by using optimum
seed rate of 3-3.5 kg/ha (1 to 1.5g/2.5m2)
• Provide adequate drainage facility and avoid excess
watering of the seedlings.
2/7/2021 74
Cont’…..
• Burn the seed beds with paddy husk or dry twigs
before sowing.
• Drench the seed bed with 0.4% per cent Bordeaux
mixture or 0.2 per cent Copper oxychloride, two days
before sowing.
• Spray the nursery beds twice with 0.4% Bordeaux
mixture or 0.2 Copper oxychloride or Metalaxyl or
Mancozeb at 20 and 30 days after germination.
• Soil incorporation of Trichoderma viride or T.
harzianum in seed beds one week before seed sowing
and thereafter Bordeaux mixture should be sprayed at
0.4 per cent.
2/7/2021 75
2. Root rots
• Caused by Rhizoctonia spp.
Symptoms ;
• Root rot is wide spread and destructive.
• The fungus causes different types of symptoms, viz.,
seedling disease and root rot.
• Germinating seedlings of one to two weeks old are attacked
by the fungus at the hypocotyl and cause black lesions,
girdling of stem and death of the seedling, causing large gaps
in the field.
• In sore-shin stage (4 to 6 weeks old plants), dark reddish-
brown cankers are formed on the stems near the soil surface
which later turns dark brown or black and plant breaks at the
collar region leading to drying of the leaves and subsequently
the entire plant.
2/7/2021 76

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20
Cont’….
2/7/2021 77
Cont’…..
• Pathogen
✓ The fungal hyphae are septate and fairly thick and
produce black, irregular sclerotia which measure 100 μm
in diameter.
• Disease cycle
✓ The disease is mainly soil-borne and the pathogen can
survive in the soil as sclerotia for several years.
✓ The spread is through sclerotia which are disseminated by
irrigation water, implements, heavy winds and other
cultural operations.
2/7/2021 78
Fig 4. Disease cycle of root rots of trees caused by Armillaria mellea.
2/7/2021 79
Cont’….
❖ Favorable Conditions
• Dry weather following heavy rains, high soil temperature
(35-39oC), low soil moisture (15-20%), cultivation of
favorable hosts like vegetables, oil seeds and legumes
preceding cotton and wounds caused by ash-weevil
grubs and nematodes.
❖ Management
• Treat the seeds with Trichoderma viride @ 4g/kg or
Pseudomonas fluorescens @ 10g/kg of seed.
• Treat the seeds with Carboxin or Thiram at 4 g or
Carbendazim at 2g/kg.
2/7/2021 80

21. 2/7/2021
21
Cont’….
• Spot drench with 0.1% Carbendazim or 0.05%
Benomyl.
• Apply farm yard manure at 100 t/ha or neem cake at
2.5t/ha.
• Adjust the sowing time, early sowing (First Week of
April) or late sowing (Last week of June) so that crop
escapes the high soil temperature conditions.
• Adopt intercropping with sorghum or moth bean
(Phaseolus aconitifolius) to lower the soil temperature.
• Grow resistant varieties
2/7/2021 81
3) Fusarium wilt
❖ Symptoms
• The disease affects the crop at all stages.
• The earliest symptoms appear on the seedlings in the
cotyledons which turn yellow and then brown.
• The base of petiole shows brown ring, followed by
wilting and drying of the seedlings.
❖ Pathogen
• The fungus produces three types of spores.
✓ Macroconidia are 1 to 5 septate, hyaline, thin walled,
falcate with tapering ends.
2/7/2021 82
Cont’…..
✓ The microconidia are hyaline, thin walled, spherical or
elliptical, single or two celled.
✓ Chlamydospores are dark coloured and thick walled.
• The fungus also produces a vivotoxin, Fusaric acid
which is partially responsible for wilting of the plants.
❖ Disease cycle
• The fungus can survive in soil as saprophyte for many
years and chlamydospores act as resting spores.
• The pathogen is both externally and internally seed-
borne.
• The primary infection is mainly from dormant hyphae and
chlamydospores in the soil.
2/7/2021 83
Cont’….
• The secondary spread is through conidia and
chlamydospores which are disseminated by irrigation
water.
❖ Favourable Conditions
• Soil temperature of 20-30oC, hot and dry periods
followed by;
✓ rains, heavy black soils with an alkaline reaction,
✓ increased doses of nitrogen and phosphatic fertilizers,
✓ soil amendment with manganese and wounds caused by
nematode (Meloidogyne incognita) and grubs of
Ashweevil (Myllocerus pustulatus).
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Cont’….
❖ Management
• Treat the acid-delinted seeds with Carboxin or
Chlorothalonil at 4 g/kg or Carbendazim@2g/kg seed
• Remove and burn the infected plant debris in the soil
after deep summer ploughing.
• Apply increased doses of potash with a balanced dose
of nitrogenous and phosphatic fertilizers.
• Multiply Trichoderma viride (2kg) in 50 kg of Farm
yard manure for 15 days and then apply to the soil.
2/7/2021 85
Cont’….
• Apply heavy doses of farm yard manure or other
organic manures at 10 t/ha. Follow mixed cropping
with non-host plants to lower the soil temperature
below 20oC by providing shade.
• Soil amendment with zinc.
• Grow disease resistant varieties
2/7/2021 86
Major Seedling Insect Pests
1. Cutworms
• Order: Lepidoptera Family: Noctuidae Species: Agrotis
spp
Common names:
✓ The common cutworm, turnip moth (Agrotis segetum);
the greasy cutworm, black cutworm, tobacco cutworm
(Agrotis ipsilon)
Host plants: Beans, Cabbage, Brassicas, Carrot, Cotton,
Eggplant, Maize, Peas, Peppers, pea, Potato, Sesame,
Sorghum, Tea, Tomato, etc
2/7/2021 87
Cont’…..
❖Distribution: They are widely distributed throughout
the world.
• Cutworms (Agrotis spp.) occur in Africa from the
Cape town to the Mediterranean Coast.
• Agrotis ipsilon is one of the most widely distributed
species of the cutworm complex.
• Distribution of Agrotis segetum is limited by
temperature.
• In Africa this cutworm is absent in the inner Sahel
since the climate is too harsh.
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Cont’….
❖ Feeding habit: Polyphagous. The larvae are known to
feed on barley, oats, tobacco, pulses, cabbage, potato,
beetroot, peas, etc.
❖ Biology and Ecology of Cutworms
• The eggs are ribbed, globular and small (about 0.5 mm
in diameter).
• When newly laid they are cream colored turning reddish-
yellow to blackish before hatching.
• Eggs are laid singly or in small groups on moist soil, on
weeds or on the stem and lower leaves of host plants or
on low growing vegetation.
2/7/2021 89
Cont’….
• A single female may lay up to 2000 eggs.
• Preferred substrates are densely growing plants
relatively low to the ground and fine-textured plant
debris in untilled fields.
• Damp, low-lying areas within untilled fields are
particularly attractive for egg-laying moths.
• Eggs hatch in 10 to 28 days.
2/7/2021 90
Cont’……
❖ Young caterpillars are pale, yellowish-green with a
blackish head.
❖ Older caterpillars have a plump body; their colour
varies from grey, dark green to brown or black with
shiny, greasy-looking skin.
❖Fully-grown caterpillars are 4 to 5 cm long.
❖ Newly hatched caterpillars feed on the leaves and
later on the stems.
2/7/2021 91
Cont’….
❖ Older caterpillars feed at the base of plants or on roots
or stems underground.
✓ They are nocturnal and hide in the soil or under stones
and plant debris during the day.
✓ At night they move up to the soil surface to feed.
Caterpillars construct burrows or tunnels in the soil about
2.5 to 5 cm deep near the host plant.
✓ They pupate in an earthen cell in the soil.
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24
Cont’…..
• The pupae are about 1.7 to 2.5 cm long, smooth and shiny
reddish-brown with two dark spines at the tip of the
abdomen.
✓ They appear almost black in colour just before the moth
emerges.
• The adult is a medium-sized moth, about 2 cm long with a
wingspan of 4 to 4.5 cm.
✓ The forewings are grayish-brown with black lines or
kidney-shaped markings along the side margins.
✓ The hind wings are pearly white with dark brownish
margins and veins.
✓ They are active at night.
✓ The life cycle can be completed in 6 weeks under warm
conditions.
2/7/2021 93
Cont’….
Damage: Young caterpillars feed on leaves and
later on stems.
Mature caterpillars cause the most damage.
They are capable of eating or destroying the entire
plant.
They girdle and cut-off young seedlings at ground
level during the night, dragging them into the tunnel
in the soil and feed on them during the day.
2/7/2021 94
Cont’….
In maize, caterpillars will feed on leaves, silk, and ears.
In beans, caterpillars feed on leaves, buds, flowers, and
pods. Larger caterpillars tunnel into and destroy the
bean pod and seeds.
On tubers and root crops, cutworms feed on tubers and
roots, boring a wide shallow hole.
Thick-stemmed vegetables such as lettuce
and brassicas may have the stem below the ground
completely hollowed out.
Attacked plant wilt and die.
2/7/2021 95
Cont’…..
Management strategies:
• Hand picking and destruction of larvae. Hand picking of
caterpillars at night by torch or very early morning before
they return into the soil is useful at the beginning of the
infestation.
• Using baits
• 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
field. If the field is planted soon after land preparation
some cutworms may be alive and attack the new crop.
2/7/2021 96

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Cont’…..
• 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
soil.
• Chemical spray
2/7/2021 97
Cont’….
2. Two spotted crickets
• Order: Orthoptera, Family: Gryllidae, Species:
Gryllus bimaculatus
• Distribution: The two-spotted cricket Gryllus
bimaculatu, which is one of the most abundant
cricket species, inhabits the tropical and subtropical
regions of Asia, Africa, and Europe.
• Feeding habit: They are Polyphagous.
2/7/2021 98
Cont’…..
• Loss: has been reported on germinating seeds and
seedlings of cotton, groundnut pods, young tobacco,
coffee, etc. Young seedlings will be cut off and drag
in to the ground where they live.
• Control:
Seed dressing to the young at susceptible stage
Chemical spray
2/7/2021 99
Cont’….
3. Clay grass hopper
• Order: Orthoptera, Family: Acrididae, Species:
Aiolopas spp.
• Description:
✓ Adults are black, brown, yellow, or green.
✓ Enlarged hind legs for jumping.
✓ Many have brightly colored underwings.
✓ Nymphs are similar but smaller.
2/7/2021 100

26. 2/7/2021
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Cont’…..
• Life Cycle: Some species have fairly elaborate courtship.
✓ Mating itself may take up to one hour, and male may ride
on back of female for a period of a day or more, a behavior
known as mate guarding.
✓ Females oviposit in loose soil (typically), among plant
roots, in rotting wood, or even in dung.
✓ Clutches consist of 10-60 eggs, and females may lay up to
25 clutches over several weeks.
✓ Oviposition typically occurs in late summer, and the egg (as
a developing embryo) overwinters.
✓ Eggs then hatch in spring.
✓ Life cycle is typically one year. A few species overwinter
as juveniles (nymphs).
2/7/2021 101
Cont’….
• Nature of damage: They cause local damage to the
seedlings.
✓ They mainly attack cereals.
✓ They have two generations.
✓ The first generations feed on the young seedlings at the set
of rainy season, while the second generations feed on milky
grains at the beginning of dry seasons.
✓ The eggs are deposited by first generations.
• Distribution: low lands of Shoa, Wollo, Gondor, Sidamo,
Harar.
• Control:
✓ Chemical, Natural enemies such as blister beetles, ground
beetles, predatory flies, parasitic flies, and especially birds.
2/7/2021 102
Cont’….
4. Termites
• Order: Isoptera, Family: Termitidae, Species: two
species (macro terms and micro terms).
• Macro terms: Bellicosus spp. They are tropical
insects.
✓ They are polyphagous and known as bark eaters.
✓ They also feed on grasses and soils.
✓ They build mould above the ground which interferes
with agricultural activities.
2/7/2021 103
Cont’….
• Macro terms: They are polyphagous and feed on
grasses, young seedlings, roots and woods. They do
not build mounds.
✓Generally termites attack cotton, groundnut,
sorghum, maize, wheat, coffee, etc. they also affect
houses, poles and bridges.
• Distribution: Widely distributed in Ethiopia and the
main problem in Wollega parts.
• Control:
Chemical
Distraction of mounds
Using entomopatogenic fungi.
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27
Cont’….
5. Chafer grubs
• Order: Coleoptera, Family: Scarabaeidae,
• Distribution: They are widely distributed throughout
the world.
• Feeding habit: Polyphagous (feed on maize,
sorghum, wheat, pastures, sugarcane, groundnut,
beans, etc). The larvae are known to feed on
underground parts while adults feed on leaves and
flowers.
2/7/2021 105
Cont’….
• Control:
Deep plowing at dry season.
Compacting soil
Sanitation.
Seed dressing.
Crop rotation.
2/7/2021 106
Cont’…
6. Gojam seed ant
• Order: Hymenoptera, Family: Dorylus
• Loss: they feed on soft parts of the tap root and
bark at the ground level.
✓They are important in high altitude vegetables of
tap root.
✓ Exhibit wilting and drying of soft parts of
taproot. Predominantly found in high compost,
manure and irrigated areas.
2/7/2021 107
Chapter 4
MAJOR DISEASE AND INSECT PESTS OF
FIELD CROPS
4.1 Major Disease of Field Crops
❖ Major Maize Diseases
1. Gray Leaf Spot (GLS)
• Caused by the fungus Cercosporazeae –maydis
❑ Symptoms: GLS characterized by tan coloured small
rectangular lesions on the leaf with the long axis of the lesion
oriented along the length of the leaf .
✓ These lesions have characteristically straight edges parallel to
the leaf veins.
✓ Large gray to black blotchy lesions can develop on the husks
and leaf sheaths under heavy disease pressure.
✓ Extensive leaf blight may occur until all the leaves are killed
resulting in stalks breakage and lodging
2/7/2021 108

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Cont’…..
❖ Disease Cycle ; C. zeae-maydis is known to infect
only maize and the pathogen is not reported to be
seed-borne.
• Infected maize debris on the soil surface is the
primary source of inoculums for GLS.
• Disease development is favoured by warm
temperature, high relative humidity and extended
period of leaf wetness.
❖ Ecology: GLS has become the principal maize
disease in warm and humid areas of the country
(Jimma, Ilubabor and Sidama zones)
2/7/2021 109
Cont’…..
❖ Control ; control primarily relies on the use of resistance
hybrids.
• Maize varieties such as BH 660 and 30H83 are attacked
less by GLS and can be recommended for high GLS risk
areas.
• Crop rotation and stable management and their
integration with resistant varieties are major factors to
control the disease.
2/7/2021 110
Cont’…..
2. Turcicum leaf blight
• Caused by the fungus Helminthosporium turcicum pass.(
syn. Exserohillium turcicum, Bipolaris turcica, Drechslera
turcica)
❖ Symptoms: Long , elliptical, grayish-green or tan lesions
ranging from 2.5 to 15 cm in length develop first on the
lower leaves.
• The disease progresses upward on the plant. Severe
infection causes a prematurely dead and gray appearance
that resembles frost or drought injury.
• In damp weather, large numbers of grayish –black spores
are produced on the lesion, often in concentric or target like
zones. The ears are not usually infected.
Fig. 2 Turcicum leaf blight symptom on maize leaf
2/7/2021 111 2/7/2021 112

29. 2/7/2021
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Cont’…..
❖ Disease cycle: The fungus survives as mycelium
and conidia in infected leaves, husks and other
plant part.
• Conidia are wind borne over long distances to
leaves of maize plants.
• Secondary spread within and between fields
occurs by conidia produced abundantly on leaf
lesion.
2/7/2021 113
Cont’…..
❖ Ecology: It occurs sporadically in most humid areas of
the world where maize is grow.
• The disease also attacks sorghum, sudan grass, Johnson
grass and others.
❖ Control: Integration of varietal resistance with
cultural control methods such as inter cropping maize
with haricot bean, crop rotation and destruction of crop
residues from the previous season’s maize reduces the
disease.
• Fungicides may be applied starting when lesions are
first observed whenever found practical (e.g. in seed
production fields)
2/7/2021 114
Cont’….
3. Stalk and Ear rot:
• Caused by the fungus Fusarium moniliforme (sexual stage
Gibberella zeae)
❖ Symptoms: Wilted plant remains standing when dry and
small, dark lesions develop in the lowest internodes.
• When infected stalks are split the phloem appears dark
brown, and there is a general conspicuous browning of
tissues.
• In the final stage of infection pith is shredded and
surrounding tissues become discoloured.
• Ear infection begins as white mycelium moving down
from the tip, which later turns reddish –pink in infected
kernels, the disease is common in cool and humid areas.
2/7/2021 115
Cont’….
• F.moniliforme ear rot is the most common pathogen of
maize ears occurs mainly on individual kernels or on
limited areas of the ear.
• The fungus produces mycotoxins known as fumonisins,
which are harmful to several animals’ species.
❖ Disease Cycle: The fungus develops on crop residue in
or on the soil.
• Under favorable conditions the fungi infect maize stalks
either directly or through wounds.
• The fungus is commonly seed- borne but less important
than air borne or soil- borne inoculums.
• Ears, kernels, roots or seedlings may also be infected.
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Cont’…..
❖ Ecology: Dry conditions early in the season and
warm, wet weather after silking favor development.
• High nitrogen and low K, high plant population and
damage to leaf by other diseases, insects or hail
predispose plants to infection.
❖ Control: Resistant varieties, balanced soil fertility
(avoiding high nitrogen and low Potassium) and lower
population.
• Fig. 3. Ear and stalk rot of maize caused by F.
moniliforme
2/7/2021 117 2/7/2021 118
Cont’….
4. Head Smut:
• Caused by the fungus Spacelotheca reiliana
❖ Symptom: Head smut first appears when ears and
tassels are formed, abnormal development of tassel which
become malformed and over grown by black masses of
spores that develop inside individual male florates.
• When tassel is infected all ears on the plant will be
smutted. When tassel is not infected most of the ears will
be smutted, a few non-smutted or partially smutted ears
formed.
• Plants with smutted tassels are usually dwarfed.
Fig. 4 Head smut symptoms maize
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31. 2/7/2021
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Cont’….
❖ Disease cycle: The fungus over seasons as teliospors
in crop debris and in the soil where remain viable for
several years.
• In the off season the telispores germinate and produces
basidiospores which are carried by air currents or
splashed by water to young developing tissues of corn
plants.
• The basidiospores germinate and produce a fine hypha,
which can enter epidermal cell directly.
• The cells surrounding the hypha are stimulated to
enlarge and divide, and then galls began formed.
2/7/2021 121
Cont’…
❖ Ecology: Soil temperature of 21-280c and moderate
to low soil moisture are optimal for seedling
infection.
• Other hosts are sorghum and Sudan grass.
❖ Control: Use of resistant varieties, Sanitation
measures such as removal of smut galls before they
break open and crop rotation help to control the
disease, seed treatment may also help.
2/7/2021 122
Cont’…..
5. Maize Streak Virus (MSV)
❖ Symptom: Early disease symptom begins within a
week after infection and consists of very small, round
scattered spots in the youngest leaves.
• The spots enlarge parallel to the leaf veins.
• Fully elongated leaves develop chlorosis with broken
yellow streaks along the veins contrasting with the
dark green colour of normal foliage.
Fig.5 Symptoms of streak virus on the Maize
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Cont’…..
❖ Disease Cycle : the virus is transmitted by a
leafhopper (Cicadulina spp.) which is the prevalent
vector and will transmit the virus for most of its life
after feeding on an infected plant.
❖ Control: Vector control using systemic insecticide
2/7/2021 125
4.1.2 Sorghum Diseases
1. Smut
Caused by the fungus Sphacelotheca spp.
Symptoms:
✓ Four types of smut occur on Sorghum in Ethiopia;
✓ but loose and covered kernel smut are by far the most
important in both high land and low land regions (Head
smut is more important of maize than on Sorghum and
long smut is usually limited in low land areas).
✓ Loose smut is caused by Sphacelotheca erucenta .
2/7/2021 126
Cont’…….
• It causes loose smut of the kernels and has marked
effect on growth of the plant.
• Infected Sorghum heads are characteristically looser,
bushier and have a darker green color than normal.
• Small shoots develop from tissues, which normally give
rise to the flora organs.
• Usually all the spikelets of an infected heads are
smutted and infected plants prematurely.
• Covered kernel smut is caused by the fungus
Sphacelotheca sorgi
2/7/2021 127
Cont’……
• The first noticeable symptoms are the appearance of
smutted heads.
• Individual grains or all grains in infected heads are
replaced by smut sori.
• Individual smut sori are oval or cylindrical in shape and
gray to brown in color.
• The soral membrane (Peridium) is thicker and more
permanent than in loose smut; it may persist unbroken
until threshing.
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33. 2/7/2021
33
2/7/2021 129
Fig. 1 Heads of Sorghum infected with loose smut(left),
Covered smut(center), and long smut (right)
2/7/2021 130
Disease Cycle:
❖ Loose smut: During maturation, harvesting and
threshing, grain from fields containing smutted plants
become contaminated with loose smut spores.
• When such seed is sown the young seedlings penetrated
by the pathogen, which grows within the infected plant
and ultimately sporulates in the smutted heads.
• Maximum infection occur at 20-250c.
❖ Covered smut: Persists between crop seasons in the
form of seed borne spores.
• Seed become contaminated by air disseminated spore
when smut sori rupture in the field and specially during
threshing.
2/7/2021 131
Cont’…..
• Spores can survive several years under moderately dry
conditions in which grains are normally stored.
• Such spores germinate and can infect seedlings, grow
within the plant and ultimately form smut sori in the
inflorescence.
❖ Ecology: Smuts are often very severe in areas where
high water stress conditions prevail.
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Cont’…..
❖ Control: both the smuts can be effectively controlled by
the use of suitable seed dressing fungicides.
• Seed should be selected from health fields and threshed and
stored separately to avoid contamination.
• Smutted plants and heads should be removed and burnt
before the smut spores become disseminated.
• Varietal resistance to both the smuts is also reported and
one has to select appropriate resistant cultivars to the
specific conditions in an area.
• Traditional smut management practices such as treating
seeds with animal urine and washing seed with water can
be applied when other better options are available.
2/7/2021 133
Cont’…….
2. Ergot (Honeydew of Sorghum)
• Caused by the fungus Claviceps africanae
❖ Symptom: Symptoms of the disease begin shortly after
flowering.
▪ The fungus usually only infects unfertilized flowers and
infection results in the production of sugary exudates on
the infected flowers.
▪ The exudates contain spores that can be produce still
another spore which is, in turn, disseminated to infect
additional flowers.
▪ After maturity, the infected seed produces an elongated
black horn resembling ergot of rye but which are much
larger.
2/7/2021 134
Cont’…….
❖ Control; Control of the disease is made possible by crop
rotation and by planting cultivars and hybrids that are
resistant to infection.
3. Anthracnose
Caused by the fungus Colletotrichum graminicola
❖ Symptoms: Symptoms of leaf anthracnose usually
become clearly visible about the time of boot formation.
• On susceptible varieties, small circular spots develop on
leaves and leaf midribs.
• These spots have wide margins that are red, orange,
purple or tan with straw-colored centers
2/7/2021 135
Cont’…..
• In the centers of the spots, small black fruiting bodies
(acervuli) develop.
• These acervuli with septate are diagnostic characteristics
of anthracnose.
• The disease can also infect the stalk of grain sorghum.
• There are four separate phases of anthracnose; seedling
root rot, leaf (foliar), stalk rot and seed mold.
• All four phases may occur on Sorghum within a single
growing season.
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Cont’……
❖ Disease Cycle: The Pathogen survives on infected crop
residue and on infected weed hosts (perennial grasses).
• The fungus is also seed transmitted.
• Stalk Anthracnose develops from spores produced in the
foliar phase, and is spread throughout the field by
splashing rain and wind.
❖ Ecology: Severity of both leaf anthracnose and stalk rot
is highest under warm and humid climatic conditions.
2/7/2021 137
Cont’…...
❖ Control: Clean cultivation to eliminate susceptible
weed,
✓ destruction of infected crop and weed residues at the end
of the season,
✓ crop rotation,
✓ avoiding sowing Sorghum in or near fields planted with
infected Sorghum, Johnson grass or Sudan grass in the
previous season are some of the management options.
✓ Varietal resistance is the most preferred methods of
anthracnose control.
2/7/2021 138
4.1.3 Barley Diseases
1. Loose Smut
Caused by the fungus Ustilago nuda
❖ Symptoms; Infected heads emerge earlier than the health
heads in the field.
• The membranes enclosing the spore masses are very
delicate and rupture as the head emerges.
❖ Disease Cycle: The olive brown teliospores are
dispersed by wind and lands on flowers.
• The teliospores germinate and produce infectious
mycelia which invade the ovaries and then the embryos
of developing seeds.
2/7/2021 139
Cont’……
• The fungus remains dormant until the seed germinates.
• The mycelium grows systemically within the seedling
and as the plant approaches heading, the mycelium
penetrates the head tissues and convert them to masses of
teliospores.
• Teliospores are spherical with short spines on their
surface, are lighter color on one side and measure 5-10
µm in diameter.
❖ Ecology; The disease occurs wherever the barley crops
grow.
• Ustilago nuda survives as dormant mycelium in the
embryo and endosperm of diseased seeds and is not
controlled by surface acting protectant seed dressing
fungicides.
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Cont’…..
❖ Control: Systemic seed dressing fungicides such as
Carboxin effectively controlled loose smut
• Use of resistant varieties and good cultural practices can
reduce the incidence of loose smut.
2. Covered Smut
• Caused by the fungus Ustilago hordei.
• Symptoms Covered Smut has more persistent
membranes enclosing the spore mass.
• The spore mass remain intact until the crop approaches
maturity of barley during which the smutted heads
become more conspicuous
2/7/2021 141
Cont’……
• Smutted heads tend to emerge later than health heads;
sometimes trapped in the flag leaf sheath.
❖ Disease cycle: The smutted heads are broken and
crushed during threshing and teliospores collect or
survive on the surface of barley seed also deposited in
the soil.
• The teliospores germinate at the same time as the seed
germinates.
• Infection occurs through the coleoptiles and the
mycelium advances through the host tissue and become
established behind the growing point.
2/7/2021 142
Cont’…..
• The fungus enters the ovary at flower formation and
converts the tissue into fungal, mass in the place of seed.
• Teliospores are globose to subglobose, 5-8 µm in
diameter and light olive-brown to brown with smooth
surface.
❖ Ecology: The disease is distributed nationwide. In the
farmers field where growers routinely sow untreated seed
covered smut continues to cause economic loss.
❖ Control: Covered smut can be kept under control by
treating seeds with either protective or systemic
fungicides (e.g. Imidaclopride 250gm/kg + Thiram 200
gm/kg) or by sowing resistant cultivars.
2/7/2021 143
Cont’……
3. Scald
• Caused by the fungus Rhynchosporium secalis
❖ Symptoms; Distinctive lesions formed on
coleoptiles, leaves, leaf sheaths and glumes.
• Most of the lesions occur on the leaf blade and
sheath.
• The lesions appear water soaked at the early stages
and as infection advances, the center becomes light
gray, tan or white with dark brown edges.
• Lesions are oval to oblong and are not delimited by
the leaf veins.
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Cont’…..
❖ Disease Cycle; Primary inoculums of the fungus can
exist as mycelium in the pericarp and hull of infected
seed.
• Hyphae invade the coleoptiles as it emerges from the
embryo.
• In the field, infected tissues on stubble will produce
conidia in 48 hours at 10-18 0C if it is wet.
• In the field, the fungus survives on the stable which
supports sporulation and infection of next season crop.
• Moisture is also essential for dispersal of conidia as
splashing water droplets are necessary for the release of
conidia from the sporulating lesions.
2/7/2021 145
Cont’….
❖ Ecology; Scald is a common disease of barley,
especially in cooler, semi-humid barley growing areas.
❖ Control; Barley scald is controlled either by
destruction of sources of primary inoculums (e.g.
infected seeds or crop residue in the field) or by use of
resistant cultivars.
• Rotation with non-susceptible crops, deep ploughing
or burning of infected residue can destroy inoculums.
• Many improved barley cultivars posses various degrees
of resistance or tolerance to scald.
• Seed treatment has not been adequately used; foliar
sprays may be used in seed farms and commercial
farms if found economically.
2/7/2021 146
Cont’…..
4. Net blotch
• Caused by the fungus Helmithosporium teres (Perfect
stage: Pyrenophora teres)
❖ Symptoms: Net blotch is named for the well- known
net like symptoms produced on barley leaves and leaf
sheath.
• The initial lesions appear as minute spot or streaks
which soon expand to form narrow dark brown
longitudinal and transvers streaks that produce the
characteristics net like pattern.
• The affected part of the leaf turns brow and the
adjoining tissues become chlorotic.
2/7/2021 147
Cont’….
❖ Disease Cycle: H. teres persists from one growing
season to the next as seed borne mycelium or in
infested host residue.
• Infection of barley seedlings from seed borne
mycelium is high at low temperature (i.e. 10-150C ).
• The most important source of inoculums is spores
produced on infected straw.
• Sporulation occurs when relative humidity is high
(100%) and 15-200C. The spores released and spread
by strong air current.
• Infection of barley leaves is greatest when high
humidity persists for 10-30 hours or longer.
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Cont’……
❖ Ecology: Net blotch is a common disease of barley
wherever the crop grows.
• It is most important in areas of high humidity and rain fall.
• Severity of net blotch is also related to the susceptibility
of cultivar grown.
❖ Control; Use of Pathogen free seeds or seed treated with
fungicides prevents introduction of the pathogen in to
clean fields.
• Destruction of host debris infected with H. teres is also
recommended.
• Perhaps the most effective means of controlling net blotch
is through the use of resistant cultivars.
2/7/2021 149
Cont’……
5. Barley stripe:
• Caused by the fungus Helminthosporium gramineum
(Perfect stage Pyrenophora graminea)
❖ Symptoms Symptom first appear on second and third leaf
of the seedlings and on most leaves, produced after that.
• Newly developed leaves have a yellow stripe, particularly
on the leaf sheath and basal portion of the leaf blade.
• These stripes gradually extend to full length of the leaf
and soon become necrotic.
• Infected Plants are usually stunted .
• Spikes in may infected plants may fail to emerge and
when the emerge are usually blighted, twisted and brown
producing under developed shriveled and brown grains.
2/7/2021 150
Cont’…..
❖ Disease Cycle; H. gramineum survives exclusively as
seed borne mycelium in the hull, pericarp and seed coat.
• At time of heading, conidia are produced on infected
leaves under conditions of high moisture.
• The conidia are windblown to nearby heads and seed can
become infected at all stages of development.
• The most severe infection occurs during early stage of
kernel development.
• The critical stage for infection of the germinating embryo
begins when the coleoptiles reaches the apex of the seed
and continue until the seedling emerges from the soil.
• Seedlings become infected when soil temperatures are
below 120C. Infection is reduced or prevented at
temperature above 150C.
2/7/2021 151
Cont’…..
❖ Ecology: The disease is most severe when rain
and humidity are high during heading or when
sprinkler irrigation is used.
❖ Control; H. gramineum is strictly seed-borne and
use of of pathogen free seed is a very effective
means of control.
• Seed treatment such as carboxin-thiram
formulation can give some control.
• Some systemic seed treatment fungicides are also
effective.
• Resistant cultivars also provide control.
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4.1.4. Wheat Diseases
1. The Rusts
• Rusts are not seed-borne but important diseases of
Wheat.
• Three highly specialized fungi cause Wheat rusts.
• Stem rust is caused by Puccinia graminis f.sp. tritici, leaf
rust caused by P. recondite f.sp. tritici and Stripe rust
caused by P. striiforms.
• Each Pathogen is comprised of numerous physiological
forms or race.
2/7/2021 153
Cont’…..
❖ Symptoms: Rusts are differentiated by their uredial
color and distribution.
✓Uredial of leaf rust are scattered on the upper surface
of leaf blades.
✓They are round to ovoid, orange- red and erumpent
but without conspicuous epidermal tissues at their
margins.
✓Uredia of stem rust occur on stems, leaves and leaf
sheaths of wheat.
✓Uredial pustules are conspicuously erumpent with
epidermal tissues at their margin.
2/7/2021 154
Cont’….
✓ Uredia of Stripe rust are yellow, principally on leaves
and heads and often arranged into conspicuous stripe.
✓ Uredia of all the three rust change to telial sori (dark in
color) as the host matures.
2/7/2021 155
Fig. Stem Rust
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40. 2/7/2021
40
Fig. Spore under Microscope
2/7/2021 157
Fig. Leaf Rust on Wheat
2/7/2021 158
Fig. Leaf Rust Spore Under Microscope
2/7/2021 159
Fig. Yellow Rust Disease
2/7/2021 160

41. 2/7/2021
41
Cont’….
❖ Disease cycle: Urediospores, produced in great numbers,
are most important epidemiologically.
• They are dispersed by wind to other plants and generate
new infections in about 8 days, which permit several
cycles of infections in a season.
• Toward the end of the season, urediospores production
may be followed by teliospore development within the
uredial.
• Teliospores are brown-black and persist within the sorus
to over winter.
2/7/2021 161
Cont’……
• Teliospores germinate and produce basidiospores, which
cannot re-infect wheat but are wind-borne to alternate
hosts in case of leaf and stem rusts.
• Infections on alternate hosts in case leaf and stem rusts.
• Infections on alternate hosts ultimately produce yellow
spores known as aeciospores that are wind borne to
infect wheat.
• Rust epidemics develop when compatible (susceptible)
wheat plants and rust fungi (virulent races) occur over
large areas and environmental conditions are favorable.
2/7/2021 162
Cont’…..
❖ Ecology Generally, stem rusts is a major problem of wheat
in relatively lower altitude ( 1500-1900 mas); stripe rust in
higher altitudes ( above 1900 mas); leaf rust as endemic to
all the areas.
• Stripe and stem rusts usually occur to endemic levels
especially in Arsi, Bale and central highlands and knocked
out many high yielding varieties out of production.
• Damage wheat depends on its stages of growth relative to
rust development.
• Epidemics that occur before or during flowering are most
detrimental.
• Head infections are especially damaging. Rust infections
reduce plant vigor, seed filling and root growth.
2/7/2021 163
Cont’…..
❖ Control: Rust are best controlled by resistant
cultivars.
• However, these varieties are threatened constantly
by inoculums build up of new races to which these
varieties ultimately become susceptible.
• Resistance varieties may sooner or later become
susceptible to new races of rusts.
• This needs continuous efforts to develop new
resistant varieties to the prevailing rust races.
• Avoiding monocultures of a given cultivars over
vast areas restricts rust damage.
2/7/2021 164

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Cont’…...
• Planting several genetically different cultivars in an
area create heterogeneity in wheat crops.
• Fungicides such as Propiconazole and Triadimefon
can be used in profitable wheat farms to compliment
varieties with some level of resistance.
2/7/2021 165
Cont’…
2. Septoria leaf blotch
• caused by Septoria tritici (Perfect stage Mycosphaerella
graminicola)
❖ Symptoms: The symptoms appear first as small,
irregular reddish brown leaf spot restricted by veins of
the leaf.
• As the disease develops, the centers of the lesions
become ash colored.
• The lesions extend and merge, eventually expanding
across the leaf, often resulting in complete necrosis.
• As the lesion enlarges, they lose their dark borders and
turn to a light grayish color on which dark pycnidia
appear.
2/7/2021 166
Cont’….
❖ Disease Cycle The fungus over winters on stubble,
straw or rarely on seed.
• Spores from pycnidia initiate the disease.
• Pycnidia are produced in abundance in necrotic leaves
and spores oozing from pycnidia are dispersed within
the crop by splashing rain, infecting new growth.
❖ Ecology: Wet, windy weather conditions with
temperature of 15-250C favor the disease outbreaks.
• Dry weather arrests disease development.
2/7/2021 167
Cont’…..
❖ Control: Use of relatively resistant or tolerate cultivars
is recommended.
• Rotation wheat with non-cereal crops helps to reduce
the incidence of the disease.
• Foliar fungicide sprays such as Propiconazole may be
used in seed farms and productive commercial farms.
3. Scab (Fusarium head blight)
Caused by Fusarium Spp. (F. graminearum)
2/7/2021 168

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Cont’….
❖ Symptoms: Scab is recognized by premature
bleaching of one or more of the spikelets on the
head.
• Infected spikelets often become sterile.
• Seed from blighted heads is often small and
shriveled.
• Orange to pinkish superficial mycelium often
seen on bleached spikelets.
• Small dark spots of perithecia of the perfect stage
(e.g. Gibberella zeae) can also be observed on
infected spikelets.
2/7/2021 169
Cont’….
❖ Disease cycle: Head blight fungi overwinter as
mycelium or spores in soil debris, grass and residues.
• As warmer moist weather develops, spore
disseminated by rain splash and wind come into
contact with the aerial part of the plants
• Seedlings are often infected at emergence.
• Infection of the head may take place from the pre-
emergence to soft dough stage, but infection is
favored at flowering.
• Blight symptoms most often appear after flowering,
usually following a period of continuous moisture.
2/7/2021 170
Cont’….
❖Ecology: Scab is caused by several species of Fusarium.
• The disease is especially prevalent in humid regions.
• Barley, Oats and rye are also susceptible and yield losses
from floret sterility and poor seed filling may be
important in all cereal crops.
❖Control: Use of relatively resistant variety may be
advisable.
• However, in the absence of resistant cultivars, the
integration of a number of control measures reduce level
of scab.
2/7/2021 171
Cont’…
• Fungicide seed treatment to ensure good emergence,
field sanitation to destroy crop debris and crop
sequences involving non-cereal crops are advised.
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4.2 MAJOR INSECT PESTS OF FIELD
CROPS
4.2.1. Major insect pests of maize.
1. Stalk borers
• There are many types of stalk borers belonging to
different families of Lepidoptera.
• Spotted stalk borer (Chilo partellus) (Pyralidae),
• Maize stalk borer (Buseole fusca) (Noctuidae),
• Pink stalk borer (Sesamic calamists) (Noctuidae),
• Southern cornstalk borer(Diatraea crambidoides)
(Pyralidae),
2/7/2021 173
Cont’….
• lesser cornstalk borer (Elasmopalpus lignosellus)
(Pyralidae), Papaipema nebris (Noctuidae) are
some of reported stalk borers.
• Distribution: the first three are common in
Ethiopia and major pests.
• Host range: Stalk borer tunnel in almost any
stemmed plants and, maize, sorghum, rice,
wheat, sugarcane, wild grasses are common.
2/7/2021 174
Cont’….
• Nature of damage: Stalk borers migrating from an
earlier host infest corn seedlings causing two types of
injury.
▪ Larvae that enter the plant through the lower stalk
tunnel upwards, severing the leaves from below.
▪ In this case, infested stalks are hollow and apparently
healthy green leaves wilt and die.
▪ Other larvae climb plants, enter from the top, and feed
on buds and rolled leaves.
▪ As they unfurl, the new leaves display ragged holes
which increase in size as the leaves develop.
.
2/7/2021 175
Cont’…..
• Both forms of injury result in destruction of tassels,
production of suckers and deformation of the upper
plant
• Soon after borers enter the seedlings, the stems often
break.
• Most larvae feed on tender leaves and when they
became young they bore down to the central shoot
and dead heart will be observed.
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Cont’……
• Life history: eggs of spotted stalk borer are laid under
side of the leaf in 3-5 rows containing 50-100 eggs.
▪ Hatching takes 7-10 days and fully developed larvae
measures 20-25 mm long.
▪ It is whitish to brown and has four longitudinal strips at
the back with dark brown spots and black head.
▪ Young larvae migrate to the top of the plant and then
bore in to the tunnel or else more down outside the stem
and just above the node of the stem.
▪ The eggs of maize stalk borer are laid under side of the
leaf sheath arranged in long line and hatched within 10
days.
2/7/2021 177
Cont’…..
▪ Larval stage will be 40 days and pupation is within the
stem.
▪ Maize stalk borer have two generations (1st generation
lasts 70-72 days and 2nd generation cause the great
damage).
• The eggs of pink stalk borer are laid in the inner side of
the sheath in 40 groups.
• The larva immediately bore in to leaf without feeding on
it.
• The larval period is 6-8 weeks, matured larva is about
30mm and have brown head and pink mark on the back
side.
• Pupation is within the stem.
• Economic importance of stalk borers
2/7/2021 178
Cont’….
✓ Stand reduction due to dead heart (death of central
pith)
✓ Severe stunted growth and yield loss
✓ Rotting of the crops including sorghum head
✓ Stalks become weakened and stem breakage will be
followed.
2/7/2021 179
Cont’…..
• Control: Stalk borers cannot be controlled once they have
entered the plant; therefore, control measures should
concentrate on prevention.
✓ Destruction of weeds in fields and along fence rows results
in the elimination of many primary hosts from which the
borers infest corn.
✓ Early planting.
✓ Removal of all stubbles and debris from the ground.
✓ Chemical (endosulfan, karate, cypermathrin,
chlorophysitoke), granules and dust application after 4-6
weeks of planting for small scale farmers.
✓ Where applicable, systemic insecticides may be effective
when applied in areas of highest potential damage.
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Cont’….
2. African armyworm
• Order: Lepidoptera, Family: Noctuidae, Species:
Spodoptera exempta
• Local names: In Ethiopia known as Geiry or
Temch
• Common names: Mystery worm, Barnosay
• Host plants: African armyworms cause damage to
cotton, barley, oats, wheat, maize, millets, sorghum,
soyabean, sugar cane, grasses, citrus plants, beans,
okra, cabbage, cucumbers, marrows, potatoes and
tomatoes.
2/7/2021 181
Cont’….
• Life cycle and description: 10 to 300 eggs are laid by an
adult female moth, on the leaves.
✓ The eggs are white and become dark brown just before
hatching.
✓ Depending on temperature the eggs hatch after 2 to 5
days.
✓ The caterpillar is grey-green at first, becoming black with
green undersides when fully grown.
✓ The head is black with a characteristic V mark. As
described above the caterpillar has coloured markings on
its back.
2/7/2021 182
Cont’…..
✓ The caterpillars crowd together, often moving in the
same direction, in search of food, hence the name
‘armyworm’.
✓ The caterpillar stage of its life lasts 14 to 32 days.
✓ The caterpillar buries itself in the ground to pupate.
✓ It builds a cocoon of silk and stays in it for 7 to 21
days.
✓ The pupae are brown in colour right after pupation
turning darker brown and finally almost black.
2/7/2021 183
Cont’…..
✓ They are 10 to 14 mm long, with a smooth, shiny
surface, and are enclosed in a delicate cocoon of soil
particles held together by silk.
✓ It then emerges as a grey-brown night-flying moth
with pale hind wings and a small oval white mark on
the forewings.
✓ The wingspan is roughly 28mm.
✓ An outbreak is more likely to occur if crops have
been sprayed with high quantities of nitrogen as this
causes green, sappy growth which is very attractive to
armyworm caterpillars.
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Cont’…..
• Damage: The African armyworm is a migratory moth, the
larvae (caterpillars) of which are important pests of
pastures and cereal crops.
✓ Outbreaks follow the onset of wet seasons when dry
grasslands produce new growth and cereal crops are
planted.
✓ Caterpillars are major pests in outbreak years, causing
significant losses on a local, national and regional scale.
✓ During outbreaks, caterpillars occur in such high numbers
that they have to travel in masses from one field to
another in search of food to complete their development,
devastating crops as they move.
2/7/2021 185
Cont’….
✓The economic importance of the African
armyworm is due to its rapid development (short
life cycle), high reproductive capacity, and
mobility by migration.
✓Moreover, there is little time to react as
infestations frequently go unnoticed, since young
caterpillars are difficult to detect.
✓When caterpillars become conspicuous (at the
fourth instars), they cause a lot of damage in a
very short time.
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Cont’…..
• Prevention and control
➢ Light traps: Light traps can provide useful information
about the population of moths and therefore of
caterpillars.
• Light traps help to predict if there is going to be an
outbreak
➢ Beneficial insects: Many animals, birds and insects prey
on the African armyworm at different stages of its life
cycle.
• These natural enemies should be encouraged by
maintaining natural surroundings with plenty of breeding
places for them, including trees and shrubs.
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Cont’…..
• Night birds and bats feed on the African armyworm
moths, and lacewings, wasps, parasitic wasps and
spiders eat the caterpillars.
• Areas of natural habitat: Avoid burning and
overgrazing of grasslands which are the natural habitat
and food store of the caterpillars.
✓ Burning often causes outbreaks because as soon as
temperatures rise, eggs are laid in large quantities on
the fresh new grass.
✓ Also if their natural habitat and food is unavailable
they will attack other crops
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Cont’……
• Hand-pick the caterpillars and feed these to
chickens and ducks
• Field sanitation: Cut grass weeds from bordering
fields.
✓ Remove weeds regularly to reduce breeding sites and
shelter for armyworm.
• Variety selection
• Tillage: Plough and harrow field thoroughly.
✓ Turning the soil exposes armyworm pupae to
desiccation and natural enemies.
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Cont’….
• Habitat Management: Avoid burning and
overgrazing of grasslands, which are the
natural habitat and food store of the caterpillars.
✓ Burning often causes outbreaks because as soon as
temperatures rise, eggs are laid in large quantities on
the fresh new grass.
✓ No oviposition occurs at temperatures less than 20°C.
✓ Also if their natural habitat and food is unavailable
they will attack other crops
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Cont’…..
• Natural enemies: Natural enemies should be
encouraged by maintaining natural surroundings with
plenty of breeding places for them, including trees
and shrubs.
✓ Many birds, toads, lizards, small mammals, insects
and spiders prey on the African armyworm at
different stages of its life cycle.
✓ Lacewings, predatory wasps, parasitic wasps, flies,
and spiders attack armyworm caterpillars.
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4.2.2 Major Insect pests of Sorghum
• Although maize and sorghum are unlike in many
respects, (e.g., sorghum being much more drought
tolerant than corn), they have many pests in common.
• Stalk borers, African army worm and maize aphids are
some examples of their insect pests in common.
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Cont’…..
1. Sorghum midge
• Order: Diptera, Family: Cecidomyiidae, Species:
Contarinia sorghicola
• Description
• Adult - The sorghum midge is an orange fly, the male
measuring approximately 1.3 mm in length and the
female 1.6 mm.
• Egg - Each white, cylindrical egg, 0.3 by 0.6 mm, is
attached to the host spikelet by a slender, tapering stalk.
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Cont’…...
• Larva - The newly hatched larva is colorless.
➢As it feeds on the developing grain, it gradually
becomes pale pink to a deeper pink, then orange,
and finally a darker orange or red-orange.
➢The full-grown larva, 1.5 to 2.0 mm long, is slightly
flattened and spindle-shaped, tapering to a point at
the head.
• Pupa - At first, the pupa is uniformly dark orange,
but after a few hours the head, antennae, legs and
thorax darken until they become black.
➢Only the abdomen retains the orange color.
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Cont’…..
• Distribution - The sorghum midge occurs in nearly all
areas of the world where sorghum is grown.
➢ Areas where sorghum has been grown for several years
and where Johnson grass (Sorghum halepense) is
prevalent are typically infested.
• Host Plants - Johnson grass and grain sorghum are the
primary host plants of the sorghum midge.
➢ Although the midge has been reported on and reared from
14 other grasses, these hosts generally are not considered
suitable for normal midge development.
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Cont’…..
• Damage - Larvae of the sorghum midge feed on the
ovary thereby preventing normal seed development.
➢ Infested heads appear blighted or blasted and produce
small, malformed grain.
• Life History - Sorghum midges overwinter as larvae in
aborted sorghum spikelets.
➢ They spin cocoons inside the spikelets where they may
remain in a resting stage, resistant to cold and
desiccation for as long as 2 or 3 years.
➢ Under favorable conditions, however, pupation and
emergence take place the following spring at about the
time Johnson grass begins to bloom.
➢
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Cont’….
• After mating, each female then deposits 30 to 120 eggs,
singly, in the flowering spikelets of this grass.
• The eggs hatch 42 to 60 hours later, depending upon the
temperature.
• The first two generations of the sorghum midge can be
found on Johnson grass, after which a migration occurs
to the flowering sorghum spikelets.
• Under normal summer temperatures, the complete life
cycle requires 14 to 16 days.
• Under warm (26 0C), humid conditions, at least nine
generations per year are possible.
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Cont’……
• Control
❖ Several cultural practices have been recommended
for control of the sorghum midge.
❖ These include preventing Johnson grass or other
hosts from producing heads in and around sorghum
fields before the crop blooms,
✓ planting at the time of year best suited for the variety
selected, and
✓ destroying crop residues which may contain
overwintering larvae.
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Cont’…..
• Early planting is also logical control practice.
• When a large adult population is detected at bloom, an
insecticide treatment is necessary.
• Since the larvae are protected in the seed and spikelets,
spray applications should be directed toward the
ovipositing females which are particularly abundant for
several days after the sorghum head emerges.
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Cont’…..
2. Sorghum shoot fly
• Order: Diptera, Family: Muscidae, Species: Atherigona
soccata
• Distribution: In Ethiopia Recorded between 800 and
2300 meter above sea level, with higher infestations at
the lower altitudes.
➢ This pest is found throughout the year when hosts are
available at the right stage. Highest population levels are
observed in August and September.
• Main hosts: Sorghum
• Alternative hosts: Maize, Finger millet, Bulrush millet,
Rice, Wheat, Several species of grasses
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Cont’……
• Nature of damage: The maggots bore into the shoot
of young plants, a week after germination to about
one month and as a result the central shoot dries up
resulting in ‘dead hearts’.
✓ If it is a little later the mother plant may produce side
tillers.
✓ But the tillers also may be attacked. The infestation
often goes as high as 60%.
2/7/2021 201
Cont’…..
• Management strategies:
➢A higher seed rate is adopted and the affected
seedlings are pulled out and destroyed.
➢Application of10% phorate (Thimet) or carbofuran
3% granules at the time of sowing at the rate of 2.5
kg a.i./ha.
➢Spraying of endosulfan @ 0.07% or cypermethrin
@ 0.005% or cartap hydrochloride 0.5 kg a.i. /ha or
triazophos @ 0.5 kg a.i. /ha twice a week after
sowing or during second week.
2/7/2021 202
Cont’…..
3. Sorghum Chafer
• Order: Coleoptera Family: Scarabaeidae Species:
Pachnoda interrupta
• Main hosts: Sorghum, Pearl millet, Maize
• Alternative hosts: Flowers of cotton, Citrus spp, and
few other plants
• Distribution in Ethiopia: 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.
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Cont’…..
• Insect biology & recognition: The spherical eggs have
a diameter of 1.6-1.7 mm.
✓ They are straw coloured.
✓ The larvae are White grubs which probably feed on
cattle dung. Pupation takes place in the soil in an earthen
cocoon.
✓ Adults are large beetles of up to 15 mm long.
✓ The colour is black with red or yellow spots.
✓ However, coloration is very variable, from nearly
complete black to complete pale yellow individuals.
• Control: At present there is a lack of efficient control
methods. But, trapping shows promise for reduction of
the pest population. Host plant resistance, sowing date
modification and intercropping can also be employed.
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Cont’…..
4.2.3 Major insect pests of barley
• Barley crop can be affected by many insect pests
1. Barley Fly (Seguy)
• Order: Diptera; Family: Anthomyiidae; Species: Delia
arambourgi
• Main host: Barley
• Alternative hosts: Maize, Wheat, Bulrush millet, Tef,
Some grasses
• Importance in Ethiopia: major pest of barley and teff
and minor pest of wheat.
2/7/2021 205
Cont’..
• Damage: 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 larva 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.
• Life cycle: Usually the eggs are laid on the soil within a
few cm distance of the plant.
✓ Sometimes they are found on the tips of the leaves. They
hatch after 3-4 days.
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Cont’…..
✓ The young larvae after hatched climb the plant to just
above the first leaf sheaths.
✓ Then they bore through the tissue to the growing point.
✓ These results in the death of the central shoot ("dead
heart").
✓ After the second molt the larva attacks another shoot of
the same plant or of another plant by eating through the
leaf sheaths.
✓ Before reaching maturity at about 12 days after hatching,
the larva moves to 3 or 4 shoots.
✓ When mature the white larva (maggot) is about 5 mm
long.
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Cont’…..
✓ Pupation takes place in the soil near the roots of the
plant.
✓ The pupal period is about 7 days.
✓ The adult is a medium sized fly of about 7-8 mm
length.
✓ It looks rather like a small house fly.
✓ The grey female has a pointed abdomen.
✓ The male is blackish and has a rounded abdomen.
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Cont’…...
2. Barley Aphid; Russian Wheat Aphid
• Order: Homoptera; Family: Aphididae;
Species:Diuraphis noxia
• Main hosts: Barley, Wheat
• Alternative hosts: Other cereals, Grasses
• Importance in Ethiopia: Major pest of barley and
wheat and minor pest of tef.
• Distribution in Ethiopia: A serious pest in the
highlands at 2400 m above sea level and higher.
• Damage: Infested plants show yellow streaks along the
veins.
✓ The leaves curl inwards and the plants remain stunted.
This species is known to be a vector of virus diseases. It
is most serious in dry weather conditions.
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Cont’…
• Insect description: the adult is found in two forms.
• Apterae (wingless aphid): The length is 1.4 to 2.3 mm.
✓ They are pale yellow green or gray green and dusted with
a white wax powder.
• Alatae (the winged aphid): The length is 1.5 to 2.0 mm.
They have a pale green abdomen.
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Cont’…..
4.2. 4. Major insect pests of Wheat
1. Welo Bush Cricket (Degeza)
• Order: Orthoptera; Family: Tettigoniidae;
Species:Decticoides brevipennis
• Main hosts: Wild grasses, Meskel daisies
• Alternative hosts: Tef, Wheat, Barley
• Importance in Ethiopia: Major pest of Tef and
Wheat and Minor pest of Barley
• Damage: They feed on the milky grains of tef and
other late sown cereals.
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Cont’……
• Description: Nymph and adult: Nymphs and adults look
very much the same.
✓ They are brown or greenish insects with long thin
antennae.
✓ The hind legs are adapted for jumping. Adults have short
wings which are useless for flying.
✓ The length of the body is up to about 25 mm.
✓ Adult females have a long, curved ovipositor which is
about 2 cm long.
✓ This species feeds on wild grasses and meskel daisies
until they dry up in October.
✓ Then they can do serious damage to the milky grains of
tef and other late sown cereals.
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Cont’….
2. Wheat Aphid (Greenbug)
• Order: Homoptera; Family: Aphididae; Species:
Schizaphis graminum
• Main hosts: Many cereals and grasses
• Importance in Ethiopia: Major pest of wheat and
minor pest of barley.
• Damage: The aphids are found in colonies on the
plants. Sap sucking on the leaves often causes
yellowing and other phytotoxic effects.
✓ This species is known to be a vector of virus diseases.
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Cont’…..
• Insect description: The apterae are small aphids with a
rather elongate oval shape.
✓ The head and prothorax are yellowish or greenish straw
coloured.
✓ The rest of the thorax and the abdomen are yellowish
green to bluish green with a darker spinal stripe.
✓ In alatae the head and prothorax are brownish yellow.
The abdomen is yellowish green to dark green.
✓ In both apterae and alatae the siphunculi are pale but
usually have dark apices.
✓ Both are 1.3 to 2.1 mm long.
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Cont’……
4.2.5 Major insect pests of teff
1. Black Tef Beetle
• Order: Coleoptera; Family: Chrysomelidae;
Species:Erlangerius niger
• Importance: Major pest of tef and minor host of wheat
• Damage: The adult beetle is the damaging stage.
✓ If feeds on the milky grains and sometimes on the
leaves. Crop losses of up to 16% have been recorded.
• Insect description: Not much is known about the
biology of this species, but a black shiny beetle up to 6
mm long.
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Cont’…...
2. Mendi Termite
• Order: Isoptera; Family: Termitidae; Species:
Macrotermes subhyalinus
• Main hosts: Polyphagous on a wide range of plants
• Importance in Ethiopia: Major pest of tef and Minor
pest of Barley, Maize, Wheat, Millets, Sorghum, Peppers
and several other crops.
• Distribution in Ethiopia: The species is found
throughout the country but it is especially a problem in
the western regions.
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Cont’…..
• Damage: The termites damage stem and roots, which is
especially serious in seedlings.
✓ Often they cut the base of the plant at ground level.
✓ Tree trunks or plant stems are covered with runways
composed of plant fragments, soil and saliva.
✓ Underneath this protecting cover they feed on the bark.
✓ Small plants may be killed.
• Insect biology & recognition: These termites live in
colonies which consist of reproductive forms (queens
and kings) and sterile workers and soldiers.
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Cont’…...
✓ They build large mounds which are called "termitaria".
✓ Because of this, their presence in an area is usually obvious.
✓ Adults are pale brown in colour.
✓ They are about 8-15 mm in body length.
✓ The wings (if present) are up to 35 mm long and have a
yellowish tinge
✓ At the beginning of the rainy season the colony produces a
number of sexual matured, winged males and females who
leave the nest.
✓ After swarming these queens and kings loose their wings and
start new colonies.
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Cont’….
• The workers which form the majority of the population
are wingless and sterile.
• They collect plant material which they take back to the
nest.
• In special underground chambers they construct fungus
gardens.
• The termites feed on these fungi.
• The wingless soldiers are recognized by their modified
mouthparts and strongly chitinized heads.
• Their function is to defend the colony.
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CHAPTER 5
MAJOR INSECT PESTS OF INDUSTRIAL
AND CASH CROPS
5.1. Cotton pests
• Seedling pests: (termites, cut worms, flea beetles)
• Sucking pests: cotton aphids, Jassids (Embasca lybica),
white flies (Bemisia tobacci), Thrips (Coliothrips
species.)
• Leaf eaters (Defoliators): Spodoptera littoralis
• Boll worms: - African boll worm (Heliothin armigera),
Spiny boll worm (Earia species), Sudan boll worm,
pink boll worm.
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