Rice tungro disease is a serious viral disease in rice-growing regions. (i) Name the causative single or viruses involved. (ii) Describe symptoms of rice tungro infection in young rice plants. (iii) Give three control strategies applicable to manage rice tungro.

1. Define each of the following terms as used in plant pathology: (i) Wilt (ii) Damping-off (iii) Mosaic (iv) Leaf scorch (v) Root rot (5 mk)
2. Define Wilt (1 mk)
3. Explain six methods farmers may use to prevent post-harvest losses due to fungal spoilage. (6 mk)
4. Define Damping-off (1 mk)
5. Give three control strategies applicable to manage rice tungro. (2 mk)
6. Define Mosaic (1 mk)
7. Define Leaf scorch (1 mk)
8. Define Root rot (1 mk)

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For each of the following pests, do the following: False codling moth, aphids, and maize stem borer. For each pest: (i) name a host crop; (ii) describe the type of damage; (iii) suggest two control measures.

1. Describe the mode of action of each of these categories of herbicides: (i) Contact herbicides (ii) Systemic herbicides (iii) Pre-emergence herbicides (iv) Post-emergence herbicides (v) Selective herbicides (vi) Non-selective herbicides (6 mk)
2. Explain five environmental factors that influence the effectiveness of herbicides. (5 mk)
3. For maize stem borer, name a host crop, describe the type of damage, and suggest two control measures. (3 mk)
4. Describe the mode of action of Post-emergence herbicides. (1 mk)
5. Describe the mode of action of Non-selective herbicides. (1 mk)

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(c) Discuss three methods used in breeding cross-pollinated crops, giving advantages and disadvantages of each method.

1. Outline four desirable characteristics for a new crop variety in drought-prone areas. (4 mk)
2. Discuss a third method for breeding cross-pollinated crops, with advantages and disadvantages. (2 mk)
3. Genetic drift (1 mk)

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(c) Explain epiphytotic disease: (i) Define the term. (ii) Describe four environmental and biological factors that can lead to epiphytotics.

1. Describe four environmental and biological factors that can lead to epiphytotics. (1 mk)
2. Describe three disadvantages of using chemical pesticides compared to biological control. (3 mk)
3. Identify a fifth viral disease of a major crop in Tanzania, naming the crop, virus, and one symptom. (1 mk)

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(c) Define each of these: (i) Quarantine (ii) Resistant variety (d) Give four advantages and three limitations of using resistant crop varieties to control plant diseases.

1. Give five symptoms indicating nutritional deficiency in maize plants. (5 mk)
2. Define Resistant variety (2 mk)
3. Suggest two control measures suitable for smallholder farmers. (1 mk)
4. Give four advantages and three limitations of using resistant crop varieties to control plant diseases. (2 mk)

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