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State the main groups of disease organisms.
2. Identify important crop diseases based on their symptoms.
3. Explain the stages of disease development and mode of transmission.
4. Identify and describe damages to crops. 5. State preventive and control measures.

These are very small unicellular organisms. They are said to be ubiquitous because they can be found everywhere even in the remotest places where other plants and animals cannot live. They are found in soils, dirty water, air. plant and animal bodies, can only be seen under the mi

The attack of bacteria on plants is manifested as rottening of plant parts accompanied with very bad smell. Though most bacti are destructive as they cause disease*, some of them are useful man since they help in the following ways

: (a) Decomposition of compost
(b) Production of drinks, e.g. beer
(c) Making of butter and cheese
(d) Fixation of atmospheric nitrogen in root nodules of leguminous plants, thereby helping in increasing soil fertility.

There are three types of bacteria based on their shapes.

They are (spherical), bacilli (rod shaped) and spirilla (Spiral shaped).

2. Fungi
These are plant species but they do not possess chlorophyll stems roots and leaves.
The body is made up of myceliium which of tiny delicate branches called hyphae. The fruiting bodies originate from some of these hyphae.

The sporangia many tiny spores through which the fungus is dispersed-. fungi have no chlorophyll, they cannot manufacture their own I hey depend on their host for their food, thereby causing use hi the host plant.

1. Viruses These are minute organisms that can only be seen under the tron microscope. Plants suffering from this disease show:
(a) Coloured spots and bands on the leavesu
(b) Twisted and wrinkled leaves
(c) Stunted growth of the entire plant.

Sucking insects e.g. mealy bugs, aphids
and white flies can limit virus disease from one infected plant to a healthy one. Almost all virus diseases have no effective cure. It is advisable to prevent and control the disease as the case may be.

2. Nematodes
These are soil-borne organisms which usually attack the roots of plants. They are capable of causing considerable damage to the plant.

Affected plants show decline in productivity and the roots become distorted with enlarged growths. Soil sterilization may help to control the spread of nematodes.

Important diseases of major crops NO.


1 Smut Fungus (Ustilago spp) Maize, Rice, grain sorghum and other cereals By wind Grains are covered with large mass of spores The wole cob may be covered with mass of black spores thereby rendering them valucles Use clean seed s to plant. Treat seeds with fungicide

2 Streak Virus Maize By piercing and sucking insects Discoloured leaf surface forming streaks Reduces crop yield Early planting spray with insecticide. Rogue the affected plants

3 Blast of Rice Fungus (Pyricularia oryzae) Rice By wind Dead areas sho on lead surface Crop yield is reduced Grow resistant varieties. Treat seeds with fungicides

4 Leaf Rust Fungus (Punccinia spp) All cereals Wind and water Rust-coloured pustules develop on the leaves of the plant The leaves die resulting in poor production Early planting. Dress seed with fungicides

5 Bacterial Blight Bacteria Sorghum cowpea, etc Wind and water Yellow leaves followed by defoliation and death of stem Yield is affected Grow resistand varieties. Use clean seeds.

6 Cercorspor a leaf spot Fungus (cercospora spp) Legumes By wind Yellow leaves followed by defoliation Yield is reduced 1. Plant early 2. Uproot affected plants and burn.

7 Rosette of groundnut Virus Groundnut By aphids, piercing and sucking insects Leaves are closely packed, wrinkle and mottled The leaves curl, turn yellow and this reduces yield.

1. Plant early 2. Use resistant varieties 3. Rogue affected plants 8 Mosaic Virus

Cassava Yam By Bemisia fly Yellow pale areas on leaves Leaf distortion and stunting of plant leading to reduced yield

1. Use resistant varieties
2. Use insecticide to kill the insects 3. Destroy the affected plants.

9 Tuber Rot Nematode, fungus Yam Through soil Yam tuber becomes brown in the tissues and later becomes soft. Renders the tuber valueless

1. Destroy affected tubers 2. Use Aldrin dust 3. Use Nematicide e.g. Mucap.

10 Roo knot Nematode (Root knot eel worm) Tomato and okro Through soil borne Nematode Knots in the roots of plants Wilting and retardation of growth and low yield.

1. Crop rotation 2. Use nematicides

11 Downy mildew Fungus Onion Airborne fungus White coating on leaves Underdeveloped or small bulbs 1. Spray with sulphide of potassium

12 Sigatoka Fungus Banana and plantain Airborne fungus Chlorosis of leaves Small bunches and few fingers in bunches 1. Clean weeding and good spacing 2. Use appropriate fungicids

13 Damping off Fungus Okro Airborne and soil borne fungus Rotting of roots and wilting of leaves Yield is reduced 1. Treat soil with fungicides

14 Leaf blotch Fungus Pineapple By airborn fungus Streak on the entire leaf surface Yields are reduced Use copper fungicide to spray affected plants

15 Black arm Bacteria (Xanthomonas malyaccarum rain fungus (Phytophthora palmivora) Cotton Through the stoma Angular sports on leaves Cotton bolls rot. Use resistant varieties

Black pod Cocoa
Rain splash, insects and animals Brown spots on pod leading to rotten and black pods The pods become useless leading to reduction in yield

1. Regular weeding of farm
2. Remove and bury all affected pods 3. Spray with fungicide like perenox and Bordeaux mixture

17 Swollen shoot Virus Cocoa By Nymphs or meaty bug and white flies Swelling on the growing parts of the stem and roots Distorted leaves and reduced growth in plants.

There is underdevelopment of pods and low yield
1. Destroy all affected plants 2. Use resistant varieties

18 Freckle Fungus Oil palm By wind insects Brown spots on leaves which later dry and die Growth of palm is affected and maturity is delayed 1. Spray with fungicides such as captan, or diethane M45

19 Collar Rot Fungus (Ganoderma Lucidum) Oil palm Soil and wind borne fungus Rotting of old palms near the base of truck The disease can kill the palm tree 1. Disinfect with fungicides 2. Burn all infected trees

20 Antrannose Fungus Oil palm By wind and insects Leaves show clear spots. Spots turn dark-brown or black later and with yellow halo. Growth is affected in the nursery 1. Space germinating seedlings properly 2. Cut off affected parts of leaved and burn 3. Spray with fungicides, Cumin, Dithane M45, cAptan or Ziran in pre-nursery

21 White root Fungus (Fumes lignosus) Rubber Through the soil Leaf defoliation Taproots are attacked by fungi leading to the breakdown of their tissues. Plants die eventually 1. Burning farmland especially old trunks after clearing before planting of seedlings.

22 Mould Fungus Grains and seed By wind Formation of whitish spores on stored produce Grains or seeds are rendered useless
1. Proper drying of produce 2. Avoid dampy stores 3. Protect store from rain or flood.

23 Gummosis Fungus (Phytophhthrora spp) Citrus Through the soil and sided by moist condition The cortex of the citrus plant is killed Gum pockets occur in the cambium. There is exudation of gum from the stem The stem tissue collapse and plant may fall and die 1. Plant resistant varieties e.g. stocks or four orange and rough lemon 2. Bud citrus plants 45cm from the ground and allo no branch below 1m 3. Proper farm drainage and sanitation reduce incidence

24 Tristeza Virus Citrus Through aphid (Toxoptera citricida) Yellowing of terminal shoots in plants; there is stem pitting Growth and yield are affected. The disease can kill the citrus plants. Control by budding plants on Cleopatra tangerine, lake and Sampson. Tangelo stocks and rough lemon

1.3 Nature and Effect of Disease Damage to Crop The nature of damage caused by a disease on crops depends on the type of disease causing organism. It also depends on the crops being affected.

Generally, there is a reduction in, the yield of crops affected by the disease. The market value of the product is also reduced. It is estimated that crop diseases account for about 20% loss of yield in il crops all over the world. Disease attack also leads to i of planting materials.

7.4 Stages of Diseases Development and Transmission There are four major stages of disease development and Ission in crops.

These are: 1. Invasion: This is the stage where 'the disease causing agent comes in contact with the host plant.

2. Establishinent
At this stage the disease causing agent enters and establishes llf in the crop tissues
. 3. Injury This is the stage where the disease pathogen multiplies itself leading to the actual attack of the host.

4. Mission/Spread This is the stage where the disease organism spreads from one plant to a healthy one. The process is aided by wind, water, insects contact and others.

7.5 Prevention and Control of Crop Diseases It is better and more economical to prevent a disease from, crops than to control it when it has occurred. The sure way luting diseases, in farms is to prevent the disease causing organism from reaching the crops. This is possible through regular removal of rotten materials from the farm, routine spraying of crops planting resistant varieties and so on. However, crop diseases can be controlled in the following ways: 1. Cultural Control The techniques adopted in this control measure include: (i) Proper care for plants such as regular weeding. This practice reduces the amount of disease attack on the crops. (ii) Bunting, of farmland: This involves setting farmland on fire before cullivation. The fire helps to kill disease causing agent such as bacteria, fungi, virus and others in the soil. (iii) Karly Planting: Early planting enables the crops to escape the outbreak of some crop diseases. (iv) Practising Crop Rotation: This practice, ensures that crop which suffer from similar diseases do not follow each other in the same rotation. This is to make sure that the cycle of the disease development is disturbed. (v) Removal of dead plants and other disease harbouring agents from the farm. The source of the disease is removed when this is done. 2. Biological Control This involves the use of good resistant crops varieties to plant. It is a very successful method of controlling most seriou^ plant diseases. Over the years, scientists have developed crop types which have great resistance to some deadly crop diseases. The use of which helps to control most diseases of crops. 3. Chemical Control This involves the use of chemicals to kill the disease organism affecting the crops. For example: (i) Fungicides such as perenox. Bordeaux mixture, and copper sulphate are used in the control of fungus diseases. (ii) Virus diseases can be controlled by using appropriate chemicals such as vetox 85 to kill the vectors e.g. aphids. mealy-bugs white flies, etc. that transmit the virus diseases. (iii) Most bacterial diseases can now be treated using appropriatle chemicals (bacteriacides) such as Agrosan 5W mercurial duss and acid. (iv) Nematodes can be controlled by using nematicides such a nemagoiu and DDT. STUDY QUESTIONS 1. Suite the main groups of disease organism giving examples in each group. 2. What are the confirmatory symptoms of disease affecting grains both in the field and in the store? 3. Explain with a diagram the stages of disease development 4. List four diseases of named crops. Describe the damages done by each disease to the crops. 5. List and explain the different methods by which crop disease can he controlled. 6. Suite three ways bacteria can be useful to man in his activities. 7. List three ways a farmer could prevent a disease from affecting his crops. UNIT 8 PEST OF CROPS Objectives: Students be able to: 1. Classify insect pests into feeding groups 2. Name important field and storage pest of crops 3. Identify nature of damage to crops 4. State preventive and control measures 5. State other important pests of crops 6. Identify the nature of their damage to crops 7. State the preventive and control measures

Classification of crop insect pest into main feeding groups

A pest is an organism which causes damage to crops.
Insect pest are those insects that cause physical damage to crops. Insects belong to the group arthropoda. Generally pests reduce crop yield both in quality and quantity. 1. Biting and chewing insect pest The mouth parts of pests in this group are especially adapted to biting and chewing of various plant parts. The mouth parts are made up of two hard biting jaws (mandibles). In addition to these, they also have two jaws (maxillae). They have two lips – flat upper lip (larum) and lower lip (labium) while the maxillae are used to push the crop parts into the mouth, the mandibles are used for the biting and chewing since they are very strong. These insects can feed on any part of the plant including leaves, fruits, stems, flowers and even roots. Some common biting and chewing insect pests are beetles, grasshoppers, termites, crickets, caterpillars of moths and butter flies, locust, army worms and so on. They feed on many crops such as okro, maize, rice, vegetables, cassava and fruit trees. DIAGRAM Figure 2.8.1a: Cricket DIAGRAM Figure 2.8.1B: Beetle DIAGRAM Figure 2.8.1c: Grasshopper DIAGRAM Figure 2.8.Id: Caterpillar 2. Piercing and Sucking Insect Pests The mouth parts of these insects are shaped tike injection needles and are thus adapted to piercing (that is penetrating into the plant part) and sucking (that is removing plant fluid). These piercing and sucking habits of the insects lead to] destruction of plant tissues, development of holes through which disease organisms can enter into the plant system and transfer or harmful germs from diseased plants to healthy ones. All these lea to weakening and eventual death of the plants affected. Good examples of piercing and sucking insect pests are aphids (plant lice), cotton stainer, mealy bugs, capsid bugs, and scali insects DIAGRAM Figure 2.8.2A: Cotton Stainer DIAGRAM Figure 2.8.2b: Aphid


Boring insect Pests of crop

These are insects that bore into plant tissues and seeds, kamples are stem borers of cereals and weevils such as beans, rice M maize weevils. Other insects pests which may not fall into the above groups have been found to affect crops. An example is the weaving insect which causes the folding of the leaves of crops particularly vegetables. DIAGRAM Figure 2.8.3: Bean Weevil NO. NAME OF PEST CROPS AFFECTED NATURE OF DAMAGE TO CROPS PREVENTION AND CONTROL MEASURES 1 Stem borer (Sesamia spp) Cereals e.g. rice, maize sorghum Pest eats up the juicy centres of stems thus causing the crop to collapse and die Burn all crop remains in the farm after harvest, uproot and burn affected crops. Spray with gammaling 20 or DDT. 2 Army worms Grain crops e.g. Rice, Maize, Sorghum They eat up the leaves and stems of the crops leading to mechanical damage of crops. Plant early. Spray with an insecticide such as gammalin 20.


Ear worms Maize

These larvae bore into the cobs or ears of maize thereby eating up the fresh grains Early planting spray with gammalin 20 4 Aphids Cocoa, groundnut, cowpea They bite and pierce through the outer texture of growing plants. Sucking out the sap leading to stunting, distortion and defoliation in affected plants Spray affected crops with insecticides 5 Pod Borers (Maruca tesulalis) Legumes e.g. Cowpea They cause damage to the tender parts of the plants, by eating up the flower buds and pods. This leads to reduction in yield. Plant with resistant varieties. Spray with gammalin 20 or diagram. 6 Variegated Grasshopper (Zonocerus variegates) Yam, vegetables, rice, cassava, etc. Eats up leaves of plants. Growing point and stem may be eaten too. Spray with gammalin 20 or vetox 85 7 Yam Beetle (Heteroligus meles) Yam Feeds on tubers of yams in the soil causing holes on them Dust yam planting materials with aldrin dust before planting. 8 Cassava mealy bug (phenacoccus Manihoti) Cassava Affected plants become stunted since the internodes are reduced. The tip begins to develop bunchy tops, the leaves die off finally, the whole plant looks like a candle stick. Plant early. Dip cassava cuttings in 0.1% Rogor or ultracide solution for 1 minute before planting 9 Capsids Cocoa The insects attack young shoots of cocoa and introduce toxic saliva into the plant. This kills the plant Spraying with gammalin 20 10 Cotton stainer (dysdercus superstitious) Cotton Attacks opening cotton bolls thus staining the lint Spray with insecticide 11 Weevils Rice, maize, beans Eat up the cotyledons of stored products Spray with insectitide 12 Fruits worm The larva eats up the fruits Spray with vetox 85 13 Termites Oil palm, cassava, sugar cane, yam, etc They destroy roots and seedlings of plants especially when young Spray with aldrex 40. Water crops regularly in the dry season. 14 Boll worms Cotton They eat up succulent boll. Bolls drop off prematurely Pick and burn affected bolls. Spray with insecticides 8.3 Other Pests of Crops 1. Bird These attack mainly grain crops such as maize, rice, sorghum and barley. They also attack fruits in the field. Examples of these birds are Weaver birds (Quela), parrots, etc. DIAGRAM Figure 2.8.4: A

. (a)

Nature of disease Damage to crops

They peck out planted seeds, eat up grains on the field and destroy leaves of some plants such as oil palm. They also eat ripe fruits such as pawpaw, mango, and cashew. (b) Control: 1. Use of scare crows 2. Spraying chemicals such as furadan with aircraft, 3. Shooting with catapult or gun. DIAGRAM Figure 2.8.5: Scare Crow for birds and mammalian pest in farms. 2. Rodents These include rats, grass-cutters, African rabbits and hare. DIAGRAM Figure 2.8.6: A Rodent (Grass-cutter) (a) Nature of Damage: They cut down and eat various parts of the crop especially cereal and tuber crops. Grass-cutters eat up rice, young palm seedlings and maize plants. Rats eat up stored produce like tubers and grains. Hare eat up planted grains. (b) Control: (i) Use of poison baits (ii) Use of traps (iii) By shooting with guns, (iv) Use of rat gums.


Mammalian Pests of crop

These include monkey, deer, antelopes and bush pig. They do a lot of damage to crops in the farm by uprooting eating them up. For example, monkey eat up plantains, banana maize and cocoa pods. Control: (i) Trapping (ii) Shooting with gun. DIAGRAM Figure 2.8.7a: Monkey DIAGRAM Figure 2.8.7b: Giant Rat (Cricetomys gambianus). STUDY QUESTIONS 1. How can insect pests be classified using their feeding habits? 2. (a) Name 10 insect pests you know. (b) For each one, slate the crop it affects, the damage done to the crop and control measure of the pest. 3. (a) Apart from insect pesis, mime three other pests you blow. (b) Which crops do they affect? (b) flow can they be controlled? 4. Classify the following into hiling and chewing piercing and sucking, and boring insect pests:- Beetles, Aphids. stem boreres, caps ids, weevils, locusts, mealybugs, crickets, cotton stainer, 5. Itemise >>>>> you would use for rodents attack on your farm.

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