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The problem of pests and diseases attack on crops is a major challenge facing farmers. The incidence of pests and diseases often leads to the reduction in the quality of the crops produced and it usually results in huge losses which discourage farmers from continuous production of the crop. Most farmers eventually stop crop production after they have being faced with series of pest and diseases infestation which they cannot effectively control. An understanding of the types of pests and diseases which the different crops are prone to is paramount for a successful crop production. The pest and diseases that could affect a crop need to be firstly identified, after which necessary solutions should be proffered.
This document will give foundational knowledge of the different types of pests and diseases that attack the listed crops. Should you require any help managing the pests and diseases on your farm contact us using firstname.lastname@example.org
MAIN PESTS AND DISEASES OF MAIZE (Zea mays)
Seed corn maggot: The maggot bore into the seeds and seedlings and may result seedling death.
Seed corn beetle: Adult attack germinating seeds and seedlings, causing stunted growth.
Wireworms: Wireworm feeds at the base of young plant. It causes stunted growth and death of young plants.
Black cutworm: Cutworm feeds at the base of young plant. It cuts off young plants soon after emergence.
Maize stalk borer: Stalk borer creates holes in young unfurled upper leaves from young larvae; older larvae bore into stalk. It can cause death of the plant if stalk is affected.
Corn root aphid: The aphids pierces plant roots and cause retarded growth. Heavily infested seedlings rarely grow taller than 25 cm.
Maize aphid: Attacks are on leaves as a black fungal growth (called sooty mold) often occurs on the honeydew secreted by aphids. This can lead to reduced growth.
Maize streak Virus (MSV) Transmitted by leafhoppers: Spread in the whole plant after transmission via insects. Reduced by retarded crop growth
Common rust: Development of pustules on the upper and lower leaf surfaces.
Northern Leaf Blight: Northern leaf blight develops on the upper leaf surface. Infection that occurs during the early stage of growth may cause heavy loss in ear fill.
Grey leaf spot: The lower leaves of the corn plant are most often the sites of initial infections by grey leaf spot while the upper leaves are infected afterwards. Severe infestation can lead to premature plant death.
Ear and stem rots: Ear and stem rots infect stalks following stalk borer attack. Damage results in the failure of the ear to develop. Kernels in the ears may be infected.
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DISEASES OF OKRA (Abelmoschus esculentus)
The diseases of Okra include:
Damping off: Seedlings appear wilted, yellowed and either depressions, light brown ring-shaped lesions or water-soaked, dark green lesions are found on the collar. This disease can cause an 80% reduction in okra seed emergence. Very widespread disease mostly affects seed germination (pre-emergence damping off). When damping off occurs, seedlings emerge later and are sparse.
Fusarium wilt: In the event of a severe attack, many leaves droop and become chlorotic. This produces overall wilting of the plant which subsequently dries out and dies. Infections are most likely to occur in soils with low potassium content and high acidity.
Cercospora leaf spots / Cercospora leaf blight / Black mould: The disease weakens the plant’s assimilation capacity by diminishing the leaf area which adversely affects fruit yield. The disease shows on the lower surface of the leaves as greyish spores that later become black and sooty.
Powdery mildew of okra: On the leaves, the disease shows on both surfaces in the form of small greyish white downy spots.
Bacterial blight of okra: It causes death of seedlings and loss of young plants and several infections often cause premature leaf fall.
Several species of virus are liable to infect okra entailing varying degrees of economic impact.
Okra leaf curl virus: When a severe infection occurs at an early stage, the plant’s entire development is affected and growth is retarded or stopped.
Cucumber Mosaic virus: The leaves and fruit of affected plants tend to develop necrotic areas. Plants that are infected at an early stage remain stunted. Losses are often huge (60 to 90 %) when early infection occurs.
Cotton Yellow Mosaic Virus: This disease causes stunting, leaf chlorosis and depreciation of fruit quality. When infection occurs at an early stage, the plants remain stunted.
Hibiscus Yellow Vein Mosaic Virus: This disease is mainly transmitted by insect vector. Seedlings and plants at vegetative growth stage, flowering stage and fruiting stage are susceptible to this attack.
Okra green stink bug: Stink bugs at different stages of development feed on the sap of host plants. Stink bugs attacks okra at all stages of development with a predilection for the floral buds and fruiting stages.
Cutworms: Young caterpillars, which are yellowish green with a blackish head feed on leaves while older ones feed on plant stems. The seedling stage is the period of highest susceptibility.
Cotton aphid: Aphids attack okra at all stages of development, with a predilection for the juvenile stages. These aphids have a symbiotic relationship with ants. Ants provide protection to aphids from their predators, while feeding on the honeydew produced by the aphid.
Tobacco whitefly: Direct damage is caused by poison injected by tobacco whitefly feeding, giving rise to chlorotic areas on the leaves and sprouts of Okra plants. Okra is attacked by whiteflies at all stages of development with a predilection for the juvenile.
Cricket: Cricket feeds on juvenile shoots and leaves and hence tends to devour the terminal buds of seedlings and cut their stalks off.
Cotton semi-looper: The larvae of cotton semi-looper feed on leaves, making holes, and sometimes attacked leaves are ripped up, leaving only the midrib and veins. The insect eats all the intermediate tissue mainly on the upper, juvenile leaves.
Cotton strainers: When the insect attacks juvenile fruit, they tend to dry out and end up dropping off. Pods attacked when near maturity stage develop spots at the numerous toxic bite wound locations and dry out.
Spiny bollworms: The caterpillars feed on the content of floral buds, flowers and pods of okra plants. These organs are sometimes visibly perforated. On the pods, caterpillars dig entry points that are subsequently invaded by saprophytic fungi.
Thrips: Thrips feed on the lower surface of the leaves, on flowers and fruits. Damage results from both larvae and adults puncturing the plant tissue and sucking the exuding sap. Attacked plant parts frequently have a silvery sheen and show small dark spots of faecal material.
Mole-cricket: Mole-crickets disrupt seedbeds by digging holes and tunnels. Hence seeds either fail to germinate subsequent to attacks or else are moved thereby disrupting crop alignment.
Cotton bollworm, African bollworm: Bollworm caterpillars attack floral buds, flowers and pods. They make large holes in the leaves, eat into floral buds and perforate pods producing cavities of various sizes.
Leafhopper or jassid : Symptoms begin as yellowing of leaves, then the edges become brown or red and discolouring extends to the interior area of the leaves.
Lagriid beetle: Holes of variable size appear on the lamina as a result of the insect feeding on the foliar tissue. The economic impact of Lyillosa is minor because it is not voracious and is rarely abundant on okra except in the rainy season. Additionally, the impact of attacks is offset by production of new leaves.
Leafminers: Leaves that have been attacked by larvae become necrotic when the larvae emerge and large portions turn brown thereby reducing photosynthetic activity.
Blister beetles, flower beetles: Symptoms are visible on the leaves in the form of holes on the lamina. On floral organs, the petals, stamen and pistil are all devoured which gives rise to varying degrees of seed abortion. As a result, losses may be extensive depending on the severity of pest infestation.
Cotton seed bug: Symptoms are visible in seed production, fields on fruit whose seeds attacked during the ripening process. The seeds are often wrinkled and have tiny brown or blackish dots, which are the insect bite wounds. These bites diminish the germination capacity of the damaged seeds.
Cetonid: Adult insects attack leaves and stalks as well as young okra pods. Damage to leaves and stalks causes abnormal growth of the plant and deformities.
Flea beetle: Young seedlings are the most vulnerable to flea beetle attack. Heavy insect attacks at the initial stages of the growing season can seriously jeopardise okra yield entailing losses of 30 to 70 percentage.
Mealybug: The leaves located beneath the mealybugs colonies are covered with sooty mould thereby diminishing photosynthetic activity. Severe attacks interfere with plant growth and lead to substantial decrease in yield.
Armyworm: Damage cause by armyworm attack can be very extensive depending on the size of larval populations.
Leaf roller: Pieces of okra leaves are cut out and rolled by the leaf rollers. In many cases, when many leaves are affected, the leaf area and hence photosynthetic activity are diminished. In the event of heavy attacks, plant growth may be hindered.
Okra white grubs: Visible symptoms range from wilting to lodging of affected plants. When extremely high larval density occurs at the beginning of the rainy season in a very humus-rich, moist soil, considerable losses may be generated.
Cotton worm: The caterpillars are phyllophagous and symptoms are visible on leaves, which are devoured or from which large pieces have been cut out. Damage is generally minor as this pest is not usually very abundant in okra field.
Variegated cricket: Adults feed on the entire leaf leading to defoliation of the plants. Additionally, when massive infestations occurs, the entire plant may be devoured right down to the root at soil line level.
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PEST AND DISEASES OF YAM (Dioscorea spp.)
Defoliating caterpillars: Defoliating caterpillars eat the leaf blade and then attack the stems, sometimes causing severe damage.
Yam moth: Pyralid moth worms attack yam tubers in lofts by mining, especially during the first four months of storage.
Chrysomelids: Chrysomelids larvae are shiny, black and covered in mucus, and may reach 1 cm. They are defoliating and can cause major damage locally, especially during the first months of the crop, but without any real economic impact.
Yam beetle or weevil: Damage in the form of big holes (about few cm deep) occur in tubers and are caused by adult weevils in the fields, from the period of germination until harvest. Larvae develop on the roots of other plants (grasses) in wet areas near yam fields or directly on the yam roots.
Coffee bean weevil: The damage is caused by the hairy yellowish larvae. The brownish-red adult, which is a good flyer makes circular perforations which yield a yellow powder. Its attacks are generally confined to areas around injuries caused by harvest or caterpillars.
Macuna: The larvae cause significant local damage to the tubers. The adults, 20 mm long, eat the leaf blades and sometimes the tubers as well.
Tenebrionidae : The larvae and the adults eat into the surface of the tubers and then bore large areas 5 to 10 mm deep. Despite the significant size of the insects the damage progresses quite slowly.
Mealybug scales: These homopterae develop mainly during storage, forming a sort of white powder near the top of the tubers. They can cause complete necrosis of sprouts preventing the use of tubers as seedlings.
Yam scale (with carapace): This species sometimes grows until it totally covers tubers during storage in the form of small and more or less whitish scales. This does not cause a loss of volume but may cause germination to be delayed or even stopped.
Termites: Termites can attack the tubers during storage, with the infestation possibly beginning in the field. The damage, which may be significant within a few weeks, is often difficult to detect when the colonies use only one gallery for penetration.
Root-knot nematodes: The symptoms include the development of prominent galls on the surface of tubers. There is sometimes a proliferation of tuberous roots on these galls (hirsutism). Dioscorea alata is more sensitive to this type of nematodes than Dioscorea rotundata.
Yam nematodes: This type of nematodes causes small cracks on the surface of tubers, with the proximal parts (head) affected most. Under these lesions are brownish-black necrotised areas whose size depends on how long ago the damage occurred. The species Dioscorea rotundata is generally mostly affected.
Anthracnose: It is one of the most severe yam diseases, in particular among the species Dioscorea alata. It causes black necrotic spots on the leaves which develop along the veins. The stems can be affected as well as the end buds, thus stopping growth. In the case of a severe attack, the plants can be completely destroyed.
Other foliar spots: These fungi cause more or less dark brown spots of various shapes on the leaves: surrounded by a yellow halo (Curvularia) or with concentric circles (Sclerotium). Severe attacks can kill the plant.
Tuber wet rot: These micro-organisms cause soft wet rot on tubers. They develop during storage where there has been damage to the tuber or a hole made by an insect. The bacteria have a putrid odour from a close distance.
Yam mosaic virus, Yam mosaic virus and Yam mild mosaic potyvirus, Cucumovirus, Dioscorea baciliform virus, Potexvirus Dioscorea latent virus: Dioscorea rotundata often more susceptible than Dioscorea alata. Vectors include aphids and mealybugs.
Internal brown spots: Symptoms appear as brown nodules in the tubers and it results in decline in the quality of the tubers.
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MAIN PESTS AND DISEASES OF PEPPER
Aphids : Aphids weaken plants as they feedon plant and may cause death of young plants when present in large numbers.
Cutworms : Plant leaves and/or stem are eaten by cutworm caterpillars. Plants can be cut off when young, thereby, reducing density and harvest.
Fruit flies: Fruit flies attack on pepper results in sharp decrease in yield as fruits drop frequently even when they are not matured. Maggot-infested peppers are not marketable.
Leafminer fly : The attack of leafminer result in leave defoliation, which may lead to fruit sunscald in warm weather.
Fruit borers : Fruit borers attack may cause flower abortion, falling of young fruits, and may also result in hole development and rot in the fruits.
White flies: Whiteflies are vectors of viral diseases which may give rise to major yield losses. This is the main threat to yield posed by whiteflies. Honeydew depreciates market value of fruit.
Thrips: Thrips are vectors of the tomato spotted wilt virus. It results in significant reduction, if growth is slowed by severe attacks on young plants particularly in hot weather.
Broad mite: Fruits attacked by broad mite are deformed and unfit for sale.
Red spider mite: Spider mites can kill plants under hot and dry conditions. The attack may be considerably reduced particularly under dry hot conditions due to defoliation of plants.
Anthracnose: Symptoms appear as development of mycelium inside the fruit or stem and results in fruit infection, rendering them not marketable.
Damping off: Damping off results in death of seedlings prior to and after emergence. Development of mycelium inside the stem.
Fusarium wilt: Fusarium wilt causes yellowing of foliage and finally resuts in the wilting of plants.
Powdery mildew: Powdery mildew causes reduction in output due to the presence of the fungus at young crop stage.
Bacterial soft rot: The bacteria enter into the fruit by wounds done by insects or after cutting the stem at harvest. Fruit infected often collapse and hang on the plant like a water-filled bag. It can be a destructive post-harvest (market) disease.
Root-knot nematode: Infested plants are very sensitive to drought or irregular irrigation and plant will die if attacked at early stage.
Cucumber mosaic: Cucumber could be transmitted by aphid or mechanically.
Pepper veinal mottle: Pepper veinal mottle is transmitted by aphid.
Tobacco mosaic:Tobacco mosaic transmitted mechanically.
Tomato spotted wilt: Tomato spotted wilt is transmitted by thrips.
Chilli leaf curl: Chilli leaf curl transmitted by whitefly.
Blossom-end rot: Blossom-end rot occurs due to calcium deficiency and water imbalance. Fruits attacked byblossom-end rot are not marketable.
Sunscald: Sunscald disease occurs due to fruit exposure to direct sunlight and excessive heat.
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MAIN PESTS AND DISEASES OF PINEAPPLE (Ananas comosus)
Symphilids: Symphilids are small centipedes that feed on roots. Plants suffer from nutrition deficiency, their development is reduced. As symphilids are not present uniformly in the soil, it creates “pockets” of plants attacked by symphilids in the middle of healthy plants.
Mealybug: Mealybugs usually inhabit the axils of the leaves, the basis of suckers, the aerial roots, and the basis of the fruits. They transmit diseases and are associated with the devastating disease, pineapple mealybug wilt. Mealybugs feed on the pineapple plant sap which has impact on the size of the pineapple fruit and produces chlorotic areas.
Heart rot: Heart rot enters through the heart of the plant and causes death in contaminated plants.
Black rot: Black rot enters through the peduncle and injuries in the skin of the pineapple.
Black spot: Black spot infection starts from one fruitlet (floral cavity) of the fruits. Infected fruits are not suitable for exports as black spots develop in the fruits. Infected fruits are not suitable for exports as black spots develop in the fruits. These symptoms appear 5-6 days after the harvest.
These nematodes invade the tips of primary roots and stop them from elongating. Plant roots infected with nematodes often become more susceptible to other diseases. In addition, affected plants are often stunted. The pineapple plants infested with nematodes present the same symptoms as when suffering from nutrients deficiency and drought.
Mealybug Wilt: Wilt is a virus partly transmitted by mealybugs. It affects the root system causing leaves to turn deep pink, yellowing and wilting. As a result of this, fruits may fail to develop or remain small, fibrous and sour.
MAIN PESTS AND DISEASES OF FRENCH BEANS (Phaseolus vulgaris)
Leaf spot or leaf blight: Symptoms are easily identified in the field and generally only occur on the primary leaves, appearing as round brown spots surrounded with a darker ring, or many small regular black spots, depending on the pathogen. Under high humidity conditions, these symptoms can occur on older trifoliate leaves or ripening pods.
Halo blight of beans: It may attack the entire plant leaves, buds and seeds. After entry through the leaves, the bacteria multiply at an exponential rate within the intracellular spaces.
Anthracnose of bean: Symptoms can also be noted on all the above-ground plant parts. It induces brown lesions, first on the under side of leaf veins. The disease then spreads laterally as lenticular pale brown spots with darker brown borders that are visible on the upper surface of the leaves.
Ash stem blight or stem rot of bean: The entire plant, including the leaves, buds, roots and seeds—but mainly the stems and roots—can be attacked by this fungus. Dry rot symptoms appear on the cotyledons as blackening of growing points and the collar. Small black spots develop in the infected area.
Fusarium root rot of bean: Longitudinal reddish lesions appear at the base of the stem and the roots become necrotic and the taproot turns reddish.
Damping off, black leg and Pythium root rot: When plants are infected by these diseases, emergence after sowing is hampered and the seedlings that manage to emerge have black rotting roots. The plants suddenly wilt and soft and wet rot are noted on the roots, collar and sometimes the stems.
Damping off, Rhizoctonia black scurf: Early infection by this disease leads to seed degeneration and post-emergence decline. Later infections induce tissue necrosis and yellowing of leaves because of tissue alteration.
Collar rot, collar necrosis, pod rot, southern blight: At a quite early stage, symptoms appear as yellowing of the edges of the lowest leaves along with wet rot at the base of the collar just above the soil line. The top leaves then begin yellowing and fall. The pathogen spreads to the stem and roots and destroys the cortex. It sometimes also attacks the vascular tissues and develops in the upper branches and the tissues darken.
Angular leaf spot disease: This disease develops on the lower leaves of the plant as angular spots that are initially grey, then brown and limited by the leaf veins. The lesions can also be surrounded by a chlorotic halo with no coloured border.
Bean rust: Bean rust damage mainly occurs on the leaves, with the appearance of small (1-2 mm diameter) yellow pustules that soon turn into brownish-red spore masses in the middle of a yellow spot. The leaves wither and fall in highly infected plants.
Aphids: Aphids causes direct damage to bean plants during the vegetative and flowering phases. Aphid colonies can attack young shoots, the underside of leaves, petioles and seedlings.
Whiteflies: Direct feeding damage from whitefly adults and nymphs causes chlorotic leaf spots, which can be seen on the upper surface of leaves. Depending on the extent of whitefly colonisation, these spots can merge until the entire leaf is yellow. When whiteflies are not controlled, and their feeding is excessive, leaves can become brittle and eventually dry up and fall off.
Corn Ear Worm, Tomato Grub, Tobacco Budworm, Cotton Bollworm: The bollworm nibbles on the pods and leaves and eats the seeds. Adult females lay their eggs in the bean pods. These eggs and young caterpillars are hard to detect during bean sorting operations, so the pods can subsequently be damaged in the export packing boxes.
Leafminers: Feeding damage caused by leafminer appears as tunnelling (0.13-0.15 mm diameter) on the upper side of leaves. The shapes of these tunnels varies according to the attacked plant,but they are long, linear, and not very wide when sufficient leaf area is available. They are generally greenish to white.
Legume pod borer: The damage caused by this pest includes round bore holes in the corolla, which can turn the flowers into a brownish mass within 24 h.
Mylabris beetles: Adult beetles are 25-35 mm long. They are blackish with wide yellow or reddish transversal stripes on the elytra. The tips of the antennae are also yellow or orange. They consume the flowers (which leads to abortive pod set) and sometimes bore wide holes in the leaf blades. Entire fields can be quickly defoliated by these beetles since they often massively colonize crop fields.
Red spider mite or two-spotted spider mite: Yellow spots are noted on the upper side of leaves, while small mobile mites (0.5 mm) are found on the lower side. A very fine web may be noted when these mites occur in high numbers.
Armyworm: Young larvae feed on the superficial layer of leaves, often leaving the epidermis and large veins intact. Later instar larvae pierce irregular holes in the leaves and fully developed larvae can consume all of the leaves, leaving only the main leaf ribs.
Thrips: Punctures caused by thrips induce tissue discoloration and metabolic disorders in the plant, which thus weakens and wilts.
Looper caterpillar: The appearance of large irregular holes on the surface of leaves is a sign of looper caterpillar feeding.
Bean fly: Adult flies emerge from the pupae in the stem. The stem tunnelling causes death of young plants and heavy and early infestation often result in complete crop loss.
Bean seed fly: The larvae feed on the germinating seed, often hollowing it out completely. The seedlings may fail to emerge or be very stunted and gaps will appear in the planting.
Root-knot nematodes: The larvae penetrate the roots and settle in the vascular area, inducing swellings or galls. The shape, size and appearance of the galls varies with their age, number, the host plant, extent of attack, and environmental conditions. Under heavy infestations,the roots can become swelled and stunted.
Migratory endoparasitic nematode: Attacked plants show halted growth, reduced vigour, leaf necrosis and chlorosis, defoliation, brown, reddish or blackish root rot, and a reduction in yield.
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TOMATO (Lycopersicon esculentum)
The pests of tomatoes include whitefly, green aphid: tomato russet mite, root knot nematodes, spider mites, leaf miner(Tuta absoluta), caterpillars, cabbage looper and birds.
Diseases of Economic Importance
Southern blight: It causes rapid wilting of the whole plant which later develops into a white mould which covers the stem lesion.
Fruit rot: It causes numerous black spot and lesions which later lead to the complete rotting of the infected fruit.
Bacterial wilt: Wilt as a symptom. Browning of vascular tissue
Fusarium wilt: The symptoms includes the yellowing of the lower leaves, it eventually wilts and dies.
Early blight: Early blight affects the leaves and stems and circular lesions are noticed on infected leaves.
Tomato late blight: Tomato late blight affects the leaves and stems. Gray spots appear on the leaves which develops into white mould.
Tomato leaf mould: Symptoms appars as brown moulds on leaves are visible.
Grey leaf spot: Symptoms on leaves begin as yellowing of some areas of the leaves which later develops into gray centres with dark borders.
Verticillium wilt: It causes wilting in plants.
Yellow Leaf Curl Virus: Curling leaf appears as a typical symptom.
Tabac Mosaic Virus: Tomato Mosaic is caused by virus.
Tomato powdery mildew
Tabac mosaic virus
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