Crop Pest and Disease Control

30 Grade 8 Agriculture questions on Crop Pest and Disease Control, with worked marking schemes. 30 questions are available on this topic in full.

1. Question 1

   1 mark

   A farmer intercrops maize with beans and finds fewer pest outbreaks than in a pure maize stand. This is an example of

   A. Cultural pest control

   B. Mechanical pest control

   C. Chemical pest control

   D. Biological pest control

   (1 mark)

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2. Question 2

   4 marks

   Explain how each of the following cultural practices helps to control crop pests and diseases: (a) crop rotation; (b) proper field hygiene (removing crop residues).

   (4 marks)

   Marking scheme

   (a) Crop rotation (2 marks): changing the crop grown on a piece of land each season breaks the life cycle of pests and pathogens specific to one crop, so their populations do not build up. (b) Field hygiene (2 marks): removing and destroying crop residues eliminates hiding and breeding sites and sources of infection, reducing carry-over of pests and diseases to the next crop.

3. Question 3

   1 mark

   Which symptom on a leaf most strongly suggests a fungal disease such as blight?

   A. A single straight cut across the leaf

   B. A dry sun-scorched tip only

   C. Neat round bite holes only

   D. Dark, spreading spots or lesions with a mouldy look

   (1 mark)

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4. Question 4

   4 marks

   A farmer intends to spray a chemical pesticide on a tomato crop. State four safety precautions the farmer should observe when handling and applying the pesticide.

   (4 marks)

   Marking scheme

   Any four (1 mark each): wear protective clothing (gloves, mask, overall, gumboots); read and follow label instructions/correct dosage; spray with the wind at the back; do not eat, drink or smoke while spraying; store chemicals away from children and food; observe the pre-harvest interval; wash body and clothes after spraying; dispose of empty containers safely.

5. Question 5

   1 mark

   Which of the following is a physical/mechanical method of pest control suitable for a small kitchen garden?

   A. Applying a systemic insecticide

   B. Rotating crops each season

   C. Planting resistant varieties

   D. Handpicking and destroying caterpillars

   (1 mark)

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6. Question 6

   6 marks

   A maize farmer in Trans Nzoia inspects her crop and finds windowing (scratched leaves), ragged holes in the leaf whorls and moist sawdust-like droppings (frass) in the funnels of young plants.

   (a) Identify the most likely pest attacking the maize. (1 mark)

   (b) Explain THREE control measures the farmer can use to manage this pest, including at least ONE non-chemical method. (5 marks)

   (6 marks)

   Marking scheme

   (a) Fall armyworm (Spodoptera frugiperda). (1 mark) (b) Any THREE measures, at least one non-chemical (award up to 5 marks): - Scouting and hand-picking: regularly inspect the crop and pick and destroy the larvae and egg masses by hand (non-chemical, suitable for small fields). - Early planting and crop rotation: planting early and rotating maize with non-host crops (e.g. legumes) breaks the pest's life cycle and reduces infestation. - Use of recommended pesticides: apply an appropriate insecticide directed into the leaf funnel/whorl, following the label rate and observing safety and pre-harvest intervals. - Encouraging natural enemies / push-pull technology: intercropping with desmodium and bordering with napier grass repels the moth and traps larvae, while predators and parasitic wasps help reduce numbers. - Field hygiene: ploughing under crop residues and destroying volunteer maize to remove breeding sites. (Award marks for clear explanation; ensure at least one method is non-chemical.)

7. Question 7

   1 mark

   Which of the following is a cultural method of controlling crop pests?

   A. Releasing parasitic wasps

   B. Handpicking caterpillars

   C. Spraying with pyrethrum extract

   D. Timely planting to avoid peak pest periods

   (1 mark)

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8. Question 8

   1 mark

   A farmer in Trans Nzoia finds that his maize crop is being destroyed by fall armyworm, with ragged holes and droppings (frass) in the funnels of the young plants. Before reaching for chemicals, which environmentally friendly control method should he try FIRST for a small infestation?

   A. Uprooting the entire maize crop

   B. Handpicking and destroying the visible larvae

   C. Watering the crop more frequently

   D. Applying more nitrogen fertilizer

   (1 mark)

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9. Question 9

   1 mark

   When mixing and spraying a pesticide, the FIRST safety precaution a farmer should take is to

   A. Increase the dose beyond the label rate

   B. Eat a heavy meal first

   C. Wear protective clothing such as gloves and a mask

   D. Spray against the wind

   (1 mark)

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10. Question 10

    1 mark

    A learner observes that tomato plants in the school garden have yellowing, curling leaves and stunted growth caused by a viral disease spread by whiteflies. Which control measure targets the spread of this disease?

    A. Watering the plants more frequently

    B. Adding more nitrogen fertiliser

    C. Controlling the whitefly vectors and uprooting infected plants

    D. Harvesting the leaves for food

    (1 mark)

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11. Question 11

    1 mark

    A farmer sprays a chemical that kills insect pests on a bean crop. This chemical is best described as a(n)

    A. Fertiliser

    B. Fungicide

    C. Herbicide

    D. Insecticide

    (1 mark)

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12. Question 12

    1 mark

    A farmer notices that the same field planted with tomatoes every season keeps suffering from a build-up of soil-borne diseases such as bacterial wilt. The agriculture officer advises a cultural practice to break the disease cycle. Which practice should the farmer adopt?

    A. Planting tomatoes on the same plot every year

    B. Practising crop rotation with unrelated crops

    C. Increasing the spacing between watering days only

    D. Spraying water on the leaves every evening

    (1 mark)

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13. Question 13

    4 marks

    A Grade 8 learner inspects a kale crop and finds curled leaves covered with tiny green insects and a sticky substance.

    (a) Name the pest.

    (b) State one way the pest damages the crop.

    (c) Give one non-chemical method of controlling it.

    (4 marks)

    Marking scheme

    (a) Aphids (1 mark). (b) One damage (1 mark): sucks sap causing curling/stunting; excretes honeydew that encourages sooty mould; transmits viral diseases. (c) One non-chemical method (2 marks): spraying with soapy water/neem extract; encouraging natural enemies such as ladybirds; handpicking/pruning affected parts.

14. Question 14

    1 mark

    Practising crop rotation helps control pests and diseases mainly because it

    A. Increases the number of weeds

    B. Breaks the life cycle of pests and pathogens that build up under one crop

    C. Adds pesticide to the soil

    D. Makes the soil more acidic

    (1 mark)

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15. Question 15

    1 mark

    Which of the following would be classified as a vertebrate pest of cereal crops?

    A. Leaf miners

    B. Bollworms

    C. Quelea birds

    D. Aphids

    (1 mark)

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16. Question 16

    6 marks

    A maize farmer in Trans-Nzoia notices that the young leaves of his maize have ragged holes and 'windowing', and on opening the funnel he finds caterpillars with fine droppings inside.

    (a) Identify the most likely pest attacking the maize. (1 mark)

    (b) Explain TWO cultural (non-chemical) methods the farmer could use to control this pest. (4 marks)

    (c) State ONE precaution the farmer should observe when applying a chemical pesticide. (1 mark)

    (6 marks)

    Marking scheme

    (a) Fall armyworm (Spodoptera frugiperda). The ragged holes, 'windowing' and caterpillars with moist sawdust-like droppings (frass) in the funnel/whorl are typical of fall armyworm. (1 mark) (b) Cultural control methods (any TWO, 2 marks each): - Early planting/timely planting so the crop is established before pest populations build up, and planting at the same time as neighbours to break the pest cycle. - Crop rotation with non-host crops (e.g. legumes) to break the pest's life cycle. - Regular scouting and handpicking/crushing of the caterpillars and egg masses. - Intercropping (e.g. push-pull with desmodium and Napier/Brachiaria grass) to repel the moths and trap the larvae. - Field hygiene: destroying crop residues and weeds that harbour the pest. (Award two well-explained methods.) (c) Precaution when applying pesticide (any ONE, 1 mark): wear protective clothing (gloves, mask, overall); follow manufacturer's recommended dosage; observe the pre-harvest interval; do not eat/drink/smoke while spraying; spray when there is no strong wind; keep chemicals away from food, children and water sources.

17. Question 17

    1 mark

    Planting a crop variety that is not easily attacked by a particular disease is a control method known as using

    A. Contour ploughing

    B. Mixed cropping

    C. Green manure

    D. Resistant varieties

    (1 mark)

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18. Question 18

    1 mark

    A neem-based extract used to repel and kill insect pests on vegetables is an example of a

    A. Soil conditioner

    B. Botanical (plant-based) pesticide

    C. Synthetic fungicide

    D. Chemical fertiliser

    (1 mark)

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19. Question 19

    1 mark

    Cutworms cause damage to young seedlings by

    A. Cutting the stems at or just above soil level at night

    B. Sucking sap from the flowers

    C. Eating grain in the store

    D. Spinning webs on the leaves

    (1 mark)

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20. Question 20

    3 marks

    State three reasons why integrated pest management (IPM), which combines several control methods, is recommended over depending on a single method.

    (3 marks)

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21. Question 21

    1 mark

    A maize farmer in Trans Nzoia finds ragged holes and moist frass in the funnel of young maize plants. The pest most likely responsible is the

    A. Weaver bird

    B. Fall armyworm

    C. Cutworm

    D. Aphid

    (1 mark)

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22. Question 22

    1 mark

    Which control method uses natural enemies such as ladybirds to reduce a pest population?

    A. Cultural control

    B. Chemical control

    C. Physical control

    D. Biological control

    (1 mark)

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23. Question 23

    1 mark

    Aphids attack a crop by

    A. Eating the roots underground

    B. Sucking sap from the plant tissues

    C. Boring into the stem

    D. Cutting stems at the base

    (1 mark)

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24. Question 24

    1 mark

    Bacterial and fungal diseases in tomatoes are often spread quickly by

    A. Cool dry weather

    B. Deep ploughing

    C. Splashing water and infected tools

    D. Wide spacing between plants

    (1 mark)

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25. Question 25

    6 marks

    Explain three advantages of using biological control of crop pests instead of relying only on chemical pesticides.

    (6 marks)

    Marking scheme

    Any three, each explained (2 marks each): environmentally friendly/does not pollute soil and water; safe for humans and beneficial organisms; pests do not easily develop resistance; self-sustaining once natural enemies establish; leaves no chemical residues on food; cheaper in the long run.

26. Question 26

    1 mark

    The pre-harvest interval on a pesticide label tells the farmer

    A. How long to wait after spraying before harvesting the crop

    B. Which crop pests are edible

    C. How much water to add

    D. The colour of the chemical

    (1 mark)

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27. Question 27

    5 marks

    A maize field is attacked by fall armyworm.

    (a) Describe two signs the farmer would use to identify the attack.

    (b) Suggest three control measures the farmer can take.

    (5 marks)

    Marking scheme

    (a) Any two signs (1 mark each): ragged/window-pane feeding holes on leaves; moist sawdust-like frass in the funnel/whorl; presence of caterpillars in the funnel; damaged cobs. (b) Any three control measures (1 mark each): apply recommended insecticide into the funnel; handpick and destroy larvae; early planting; use of pheromone traps; encourage natural enemies; plant tolerant varieties.

28. Question 28

    1 mark

    While inspecting her kales, a learner finds clusters of tiny soft green insects sucking sap from the underside of the leaves, causing them to curl. To control these aphids safely on a vegetable garden meant for eating, she could spray a homemade solution made from:

    A. Petrol and engine oil

    B. Pyrethrum or soapy water extract

    C. Bleach mixed with salt

    D. Used cooking oil only

    (1 mark)

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29. Question 29

    4 marks

    Distinguish between a crop pest and a crop disease, giving one example of each.

    (4 marks)

    Marking scheme

    Pest: a living organism, usually an animal (e.g. insect, bird, rodent), that damages crops by feeding on them (1 mark) — example: aphid/fall armyworm/cutworm (1 mark). Disease: a disorder/abnormal condition caused by a pathogen (fungus, bacterium, virus) that harms plant growth (1 mark) — example: blight/bacterial wilt/mosaic virus (1 mark).

30. Question 30

    1 mark

    A maize farmer in Trans Nzoia notices funnel-shaped damage and droppings inside the leaf whorls of young plants, a sign of fall armyworm. Which is the MOST environmentally friendly first step in an integrated pest control approach?

    A. Spraying the whole farm with chemicals daily

    B. Hand-picking and destroying the caterpillars and scouting regularly

    C. Burning the entire field

    D. Ignoring the damage completely

    (1 mark)

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