CROP PEST

A pest is any organism that damages crops.

Effects of Pests on Crops
❖ They cut the root, stem, and leaf hence reducing the growth of plants, e.g. locusts
❖ They suck the cell sap from various parts of the plant reducing the growth of plants e.g.
aphids
❖ They bore into stems and fruits reducing the growth of plants e.g. stalk borer
❖ Cause diseases reducing the growth of plants e.g. viruses, fungi and bacteria
❖ Some compete with crops for water, nutrients, space and light reducing the growth of
plants e.g. weeds

❖ Dig out and eat roots and tubers of field crops e.g. rodents

Classification of Pest

Pests Description Examples

Insect Invertebrate animal with six legs, Aphids, locusts, stalk
body is divided into three parts and borer, armyworm etc.
usually two pairs of wings. Insects
are the largest group of pests.
Rodent Small mammal which has sharp front Squirrels, rats, mice,
teeth. moles, and rabbits
Bird Warm blooded egg-laying vertebrate Quelea, francolins,
and body is covered with feathers. sparrows, and crows
Pathogen Organism that causes diseases Bacteria, fungus and virus
Mammal Any vertebrate animal that gives Warthogs. baboons and
birth to live young and nourish them monkeys
with milk secreted by mammary
glands.
Weed Any plant which grows where it is Blackjack, Mexican poppy,
not wanted whose growth interferes and thorn apple,etc.
with that of the crop.

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 Classification of Insect pest according to mode of feeding
Mode of feeding Description Examples of pests
Biting and Chewing Have mouthparts adapted to Grasshoppers,
bite and chew plant tissue, Locusts,
the leaves, stems, flower Termites, Beetles,
buds, flowers, fruits and armyworm, Leaf miners
seeds.

Piercing and Sucking Have mouthparts adapted Aphids, Bagrada bug, Mealy
into a needle like stylet, the bugs, Scale insects,
proboscis, with which they
pierce plant tissue and suck
plant sap
Boring Have mouthparts specialized Weevils, Stalk borer,
for biting and chewing, but American bollworm
they tunnel into the plant
tissue, remain inside where
they consume large
quantities of the tissue

stylet

Bitting and chewing mouth part piercing and sucking mouth part

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Life cycles of pests
Metamorphosis refers to the process of physical change that insects undergo during their life
cycle. There are two types of metamorphosis: complete and incomplete metamorphosis.

Complete metamorphosis involves four different stages: egg, larva, Pupa, and adult.

Incomplete metamorphosis involves three stages: egg, nymph, and adult.

Piercing and sucking e.g. aphids

Life cycle

❖ Aphids undergo incomplete metamorphosis.

❖ They can reproduce both sexually and asexually.

Asexual mode (summer/humid/ rainy season)

Egg stage- The female produces many eggs that hatch into nymphs inside the body without
being fertilized. So female aphids are viviparous and reproduce parthenogenically
(asexually).

Nymph stage- adult females lay nymphs -they are born alive. They moult several times. They
feed on plant sap. Females can produce several nymphs a day. In a week nymphs mature to
become adults.

Adult stage- Adult aphids feed on plant sap and females start producing nymphs. Usually,
aphids are wingless and remain on the same plant during their whole life. But when they get
overcrowded some aphids develop wings and fly to other plants.

Sexual mode- (winter/dry)

(Under unfavourable conditions, asexual reproduction gives way to sexual reproduction).
❖ Before rains die out some young males aphids are produced.
❖ They undergo several moults and become sexually mature, they mate with wingless
females.
❖ The females lay eggs in protective shells to protect them against unfavourable conditions.
❖ Eggs wait for favourable conditions (the next rainy season) and then hatch into nymphs,
which develop into wingless females.
❖ These now start producing parthenogenically (asexually), so the usual life cycle resumes.

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 mate

nymph

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Locusts (biting & chewing pest)

Adult

Nymphs Eggs
(moult 4-5 times)

Locusts undergo incomplete metamorphosis.

❖ Adult female and male locusts mate
❖ Female lay eggs in protective pods underground.
❖ eggs hatch into nymph after 30 days
❖ Wilting: some pathogens block the xylem vessels hence reducing water uptake, plants
will wilt and die
❖ Spots or streaks- these are spots or lines found on the leaves or stem
❖ Nymph feeds and grows into adult after 4 to 5 moults. Nymph stage last 40 days.
❖ Adult feeds and reaches sexual maturity after 45 days
❖ Then mating occurs, female starts laying eggs thus cycle starts.

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Stalkborer (boring pest) Life cycle
Stalk borer undergo complete metamorphosis since it has a four-stage life cycle; egg, larva,
pupa and adult.

❖ Adult female and male moth mate

❖ female lay eggs in columns on a leaf or underneath sheath
❖ after about 10 days the egg hatches into larva, the caterpillar
❖ the caterpillar crawls up the plant into the funnel and start feeding on folded leaves
❖ half-grown caterpillar bores down the funnel into the stalk centre, it feeds on stem tissue
until it is fully grown
❖ mature caterpillar bores a hole in the stem and then pupates in the tunnel. Larva period
lasts for about 35 days.
❖ the pupa stage lasts for about 10 days. Adult moth emerges through the hole in the stem.
❖ two to three days after emergence, mating occurs and female moth starts to lay eggs, thus

starting another cycle.

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 Methods of Controlling Pests
Method of Aphids Locusts Stalk borer
control
Early planting so that plants will early planting. early planting.
Cultural be big enough before the increase destroy crop residues
in aphid numbers after harvesting.

Crop rotation, alternating effective weed control eliminate thick stemmed

suitable hosts with unsuitable grasses - found harbouring
ones the larvae

plant-resistant varieties if fertilization of crops to

available ensure vigorous growth
of crops
Ladybird beetle can be used to natural enemies like Telenomus isis parasitises
Biological feed on aphids birds, and mammals on eggs of stalk borer and
feed on locusts damages them.
egg parasites like Some wasps parasitise on
Small wasps feeds on larvae of stalk borer and
eggs. kill them.
Some parasitic wasps
parasitizes on pupa of stalk
borer and kill them
Spray affected plants with spray with locusts with Spread carbaryl (stomach)
Dimethoate (systemic) Dieldrin, inside the funnel of each
Chemical Aldrin (both contact) young maize/sorghum
Plant seeds dressed with and carbaryl plant.
Menazon(systemic) to protect pesticides (contact and Spray Thiodan E.C inside
seedlings during early stages of stomach) funnel of each young
growth maize/sorghum plant as
Foliar application with Malathion soon as injury is
noticed

Mechanical Water spraying: A strong Earthing-up and Use of Stalk buster

stream of water can dislodge destruction of egg pods implement to break up
aphids, particularly from the during the winter maize residues, destroying
undersides of leaves. season overwintering habitats for
Hand-picking -aphids by hand Trenching: Digging stalk borers.
trenches around fields Ploughing under egg
picking and then crushing or to trap locusts, those harboring grass, weeds and
dropping them into a bucket of that fall into the trash can provide
soapy water. trenches are buried. satisfactory control by
Sticky traps: placing sticky destroying the eggs.
traps around plants can catch
aphids as they move towards
the plants.
Vacuuming: using a handled
vacuum to suction pests off
plants
Use of all control measures in a Use of all control Use of all control
comprehensive and preventative measures in a measures in a

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IPM way to reduce pest populations. comprehensive and comprehensive and
(Integrated Cultural methods are practiced preventative way to preventative way to reduce
Pest before pests outbreak, then if reduce pest pest populations. Cultural
management) pests are there populations. Cultural methods are practiced
Biological Controls follows. methods are practiced before pests outbreak, then
Delay chemical control to allow before pests outbreak, if pests are there
biological control to take effect. then if pests are there Biological Controls
Mechanical methods are also Biological Controls follows.
included. follows. Delay chemical control to
Use insecticides as a last resort. Delay chemical control allow biological control to
to allow biological take effect
control to take effect Use insecticides as a last
Use insecticides as a resort
last resort

Biotechnical RNA Interference (RNAi): Transgenic Plants with Transgenic Plants with
Plants are genetically modified to Insecticidal Genes: Insecticidal Genes:
express dsRNA. When pests feed (These genes encode (These genes encode
on these plants, they ingest the insecticidal proteins insecticidal proteins
dsRNA which interferes with from certain Bacteria). from certain Bacteria).
gene expression, leading to the When introduced into When introduced into
suppression of essential proteins crops like sugarcane, crops like sugarcane, they
and death of aphids they make them make them resistant to
resistant to locusts. stalk borers.

Aphid-Resistant Transgenic Cas9 Technology: Cas9 Cas9 Technology: Cas9

Plants: ap hid-resistance genes protein is injected into protein is injected into the
are isolated and transferred to the locust cells and its stalk borer cells and its
transgenic crops, hence genetic material is genetic material is edited
improving their defence against edited (by removing, (by removing, adding, or
aphids and they will not be adding, or modifying modifying specific DNA
attacked by aphids. specific DNA sections). sections). Certain stalk
Certain locust genes borer genes (e.g.
(e.g. reproduction) will reproduction) will be
be targeted hence targeted hence making
making them sterile them sterile and reducing
and reducing their their population..
population.

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 CROP DISEASES

Plant disease is an abnormal condition in the plant caused by an internal disorder

(nutrition and stress) or infection (pathogens).

OR

Plant disease is a condition of plant deterioration and damage caused by various abiotic
(non living) and biotic factors (living).

Effects of diseases on crops

❖ Reduced Yields: Diseased plants often produce fewer fruits, grains, or vegetables, leading
to lower overall yields.
❖ Crop Losses: Severe infections can result in complete crop loss
❖ Stunted growth- when diseases attack a plant, it will not reach its full size.
❖ Discolouration- When a plant is attacked by disease, the leaves and stems may become
yellow, reducing photosynthesis rate leading to poor growth.

Classification of crop diseases

Causative Agent Disease group Examples

Bacteria Bacterial Diseases Bacterial wilt of Tomatoes &

Potatoes, Bacterial blight of cotton
& cowpeas, Bacterial blight of Soya
bean

Fungi Fungal Diseases Damping-off of seedlings, Downey

mildew of peas, Sorghum & Maize
smut, Powdery mildew of beans,
Early & late leaf spot of groundnut

Viruses Viral Diseases Maize streak virus, Cowpea aphid

born mosaic virus, Cassava mosaic
virus, Groundnut rosette virus

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1. Maize Streak Virus

Pathogen: Virus

Mode of infection: The virus is introduced into the plant tissue of the host plant by sap-
sucking leafhoppers. Leafhoppers acquire the virus when feeding on infected plants and then
feed on healthy ones thus transmitting the virus to them.
Once in the plant, the virus multiples and moves in the sap and reaches plant leaves causing
characteristic streaking.

Harmful effects of maize streak virus on crops

❖ Leaves turn light green with yellow stripes running parallel to the leaf veins, reducing the
photosynthetic area, growth, and yield of plants.
❖ Cobs are small and partially filled leading to reduced crop yields.
❖ Inflorescence may become sterile leading to reduced yield.

Control methods of maize streak virus

Cultural control:

❖ Use resistant varieties of maize available

❖ Remove infected plants and burn them.
❖ Early planting

Chemical control of maize streak virus

❖ Spray leafhoppers with dimethoate to kill them

2. Maize Smut

Pathogen: Fungus

Mode of infection: Fungal spores remain in the soil for several years, these spores spread to
young maize plants through wind, soil dust, and rain splashes. Fungal spores will germinate
in moist air or in irrigation or rainwater that collects on the plant leaves, ears, tassels and
other structures of the maize plant.

Spores enter plants through wounds/cuts caused by insects, animals, and poor cultivation
practices. This leads to infections that are visible within about 10 days.

Harmful Effects of Maize Smut

❖ Large blackish lumps appear on the stems leaves and cobs. These break
open to release a fine black powder (spores that spread diseases to other plants).
❖ Spores end up covering the whole grain, leading to a complete loss of Grains/cobs.

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Control methods of Maize Smut

❖ Avoid injury to roots, stalks, and leaves when cultivating, spraying, and fertilizing the
fields.
❖ Pull up and burn infected plants
❖ Plant-certified seed, if using own seeds collect them only from disease-free plants
❖ Practice crop rotation

3. BACTERIAL WILT OF TOMATOES

Pathogen: Bacteria

Mode of Infection: The pathogen is soil-borne and enters through root wounds. It Can also
spread through splash irrigation water, contaminated planting materials, and soil or
implements and feet of workers.

Harmful Effects of Bacterial Wilt Of Tomatoes

❖ Block the vascular bundles especially the xylem thus interrupting water uptake hence

temporary or permanent wilting of affected plants.

❖ Death of infected plants.

❖ Yellowing of leaves.
❖ Discolouration of the xylem vessels.
❖ Decay of the pith which may cause extensive hollowing of the stem.

Control and Prevention of bacterial wilt of tomatoes

Cultural Control Methods

❖ Use certified seeds and seedlings from the disease.

❖ Avoid using contaminated land.
❖ Leave planting land fallow for several seasons.
❖ Crop rotation between non-susceptible and susceptible crops.

Chemical Control methods

❖ Spray infected plants with antibiotics (streptomycin, ampicillin, tetracycline and

penicillin)
❖ Fumigate soil using chloropicrin or application of phosphorous acid to suffocate the
Pathogen.

Common Weeds Of Botswana

❖ Black jack (Bidens pilosa)

❖ Mexican poppy (Argenome mexicana)
❖ Thorn apple (Datura stramonium)
❖ Couch grass (Cynodon dactylon)
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❖ Witch weed (Striga asiatica)
❖ Devil’s thorn (Tribulus terrestris)

Safety measures and their importance when handling farm

chemicals
1. Before application

❖ The operator should wear suitable protective clothing such as overall, breathing mask,
gloves, boots and helmet/hat to reduce poisoning.
❖ Read the instructions on the packet carefully, and follow them to ensure the right
dilution before spraying
❖ Ensure anyone using chemicals is suitably trained to promote a safer work environment
and avoid injury.
❖ Prepare enough amount needed for application to reduce wastage and save money.
❖ Use the proper equipment suited for the chemical to ensure accurate application.

2. During application

❖ Avoid drinking or eating when applying the chemicals to prevent poisoning.

❖ Spray on a calm day to prevent pesticide particles from being carried away from the
target area by wind, potentially affecting unintended areas or harming non-target
organisms.
❖ Spray with the wind at your back /along the wind direction to avoid exposure.

3. Storage

❖ Keep pesticides in well-labelled containers to minimize poisoning.

❖ Store chemicals in a locked shed to keep them away from children, unauthorized people
and animals and avoid accidents.
❖ Keep them in a well-ventilated shed to avoid pollution and suffocation of people.
❖ Store them in tightly closed containers to avoid spillage.
❖ Keep them in high cupboards to keep them away from children and avoid poisoning.
❖ Store them in cool or dry or direct to prevent loss of effectiveness.

4. Disposal of containers

❖ Destroy and break up tins and packets that contained the chemicals to prevent re-use.
❖ Burn any paper or plastic containers in a deep hole to prevent re-use.
❖ Bury tins away from streams or dams to prevent pollution

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Appropriate Tools, Equipment, Machinery, And Materials When Handling
Farm Chemicals

A. Sprayers: There are different types of sprayers used for applying pesticides and
herbicides to crops, such as handheld sprayers, backpack sprayers, knapsack sprayers,
tractor-mounted sprayers, and aerial sprayers.
B. Dusters: Dusters are used to apply dry pesticides or dust formulations to plants or
areas infested with pests.
C. Foggers: Foggers create a fine mist of pesticide often used for indoor pest control in
areas such as greenhouses.
D. Granular spreaders: Granular spreaders are used to apply granular pesticides or
fertilizers to lawns, gardens, and agricultural fields. E.g. handheld spreaders, push
spreaders, and tractor-mounted spreaders.
E. Aerial applicators: Aircraft is equipped to spray pesticides or chemicals over large
agricultural fields.

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 Knapsack Sprayer

Name the parts of the knapsack sprayer labelled above.

Calibration of a knapsack sprayer

The aim is to determine the Spray Volume (SV), the rate at which water is applied to a
known area.

Calibration steps:

❖ Select and measure a sample/test area:

❖ Fill the spray tank with a known volume of water(l)#
❖ Proceed to spray at a normal speed and constant height until the test area is completed.
❖ Measure the amount of water remaining in the tank
❖ Determine the amount of water used by subtracting the final water volume from the
initial water volume

*Calculate the spray volume (SV) of the sprayer using the formula.

SV=Initial water volume (Vi)- Final water volume (Vf)/ Test Area = Litres/m2

*To calculate amount of spray mixture needed to spray a given field area.

Quantity of Spray mixture needed (Qm) = SV x Area of field (m2)

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Appropriate protective clothing

Name the protective the clothing worn by the applicators on the picture above.

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 CROP PRODUTION

MAIZE (Zea Mays)

A) Climatic requirements

Maize requires hot sunny climate with an evenly distributed rainfall of about 450mm during
growing season and average temperatures of 240 C.

B) Soil type and Soil pH requirements

Maize can be grown in a wide range of soils from sand to clay, provided they are well
drained. High yields are normally obtained from deep loam soils that are rich in organic
matter.

pH range of 5.5 and 7.0 is suitable.

C) Seedbed preparation

❖ Soil is prepared by ploughing to a depth of 25 cm to 30 cm.

❖ Disc the soil by breaking soil clods that may have formed.
❖ Then the seedbed is levelled and worked to medium tilth by harrowing.

D) Time of planting
In Botswana, the growing season generally occurs between October (onset) and March (end).

E) Planting of maize: maize is planted directly by seeds

❖ Seed rate: 22kg per ha though it may vary from 17 – 35 kg/ha depending on variety and
spacing adopted. One seed per planting station and at stated spacing plant population
would be 40 000 plants per hectare.
❖ Depth of planting: Maize seeds should be planted about 5 cm to 8 cm deep.
❖ Spacing: spacing between rows (inter-row spacing) is 90 cm.
Spacing within a row (intra-row Spacing) is 30 cm apart.

F) Application of manures

❖ Basal dressing
-Adding 2:3:2(22) + 1% Zn at an application rate of 1000kg/ha. The fertilizer is applied
with a planter in rows during planting.
- Kraal manure is broadcast and dug in 5 weeks before planting at the rate of 30 000kg /ha.

❖ Top dressing

Apply LAN (28%) 100kg/ ha 4 weeks after planting. The fertilizer is applied with a planter
in rows.

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G) Prevention and control of common Pests and Diseases

Common Pest: Stalk borer

Common disease: Maize streak virus
REFER TO NOTES ON STALK BORER AND MAIZE STREAK VIRUS

H) Prevention and control of weeds

1. Mechanical weed control

Control of weeds using physical means such as digging/tillage, cultivation, hoeing, slashing
and hand pulling.

2. Cultural weed control

Include all the aspects of good crop husbandry to minimise weed interference with crops e.g.
mulching, crop rotation, early planting, use of clean seeds etc.

3. Chemical Weed Control

The use of herbicides- these are chemicals used to kill weed.

Selective Herbicides – these are post-emergence herbicides that kill a specific group of
weeds and do not harm other plants. e.g. Duron and 2-4 D herbicides will kill only broadleaf
weeds but not maize plants.

Non selective herbicides-these are pre- emergence herbicides that kill any plant. They are
applied before maize is sown. E.g. Atrazine and glyphosate.

I) Recognition of crop maturity

For dry grains

❖ leaves are yellow

❖ Husks are dry and papery
❖ Grains are hard
❖ Moisture content is at about 20%

J) Harvesting of yield

Maize can be grown for fresh cobs or for dry grains. It takes 13 to 15 weeks before the fresh
cobs are ready for harvesting and at least 18 weeks before dry cobs can be harvested.

De-husking maize cobs is done traditionally by hand and knife, more especially if it is still
green. Self-propelled maize combine harvesters are also used for direct harvesting and
threshing of maize with husk.

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It is harvested and stacked for several weeks to hasten the drying out of cobs. When moisture
content is at about 12% it can be threshed and stored safely in bags or silo. In good harvests,
it may yield 4.8 – 5.5 ton/ha.

K) Storage methods- different structures made with different materials are used.

Storing maize in a crib on the ground Open-basket storage

Bins roofed with brick Metal Silos

Bag storage

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L) Marketing- the following activities are involved in the marketing of maize

• Harvesting and stocking

• Transport from the field
• Temporary storage
• Drying
• Husking
• Shelling and winnowing
• Storage, sorted and graded
• Weighing and putting in bags and pricing.
• Sold to individuals as fresh or dry and local traders through co-operatives and
BAMB

M) Relevant Legislation
1. Maize (Classification and Grading) Regulations:

These regulations apply to maize bought or sold by the Botswana Agricultural Marketing
Board (BAMB) starting from the 1974/75 crop season.
They cover aspects such as:

❖ Classification and Grading: Maize is categorized into different classes and grades based
on quality criteria.
❖ Weevil Maize: Guidelines for handling maize infested with weevils.

2. Control of Goods (Import and Export of Agricultural Products) Regulations:

These regulations govern the import and export of agricultural products, including maize.
❖ Agro chemicals act of 1999 provides for registration, licensing, promotion, advertising,
labelling and handling of agrochemicals.
❖ All imported germplasm to be registered.
❖ Local production to be protected from imports.
❖ Imported seeds should come with Phyto-pathological report.
N) Record keeping

To operate a successful and profitable production enterprise a farmer or farm manager must
maintain a set of records.

A farm Diary: A document in which important events are recorded daily. Some events (data)
may later be transferred to other record types.
There are two types of records

ii) Production records: Production records involve the activities involved in manufacturing
or producing goods. They focus on the physical aspects of production.

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a. Labour use records.
b. Machine/tractor use record.
c. Water, fertilizer, fuel use record, etc.
d. Maize crop records including areas, yields, planting and harvesting times, etc.

iii) Financial records. Financial records involve activities related to financial transactions.
These may include:

a. Profit and loss account

b. Sales account
c. Income account
d. Expenses account

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