Plant disease infection and control
Explain how named bacterial, fungal and viral plant diseases infect crops, cause harm and can be prevented or controlled.
Exam scope and assessment notes
Use this original lesson for the listed 2026, 2027–2028 and 2029–2031 Cambridge syllabus cycles. This route maps Cambridge's 2026 Version 2, 2027–2028 Version 1 and 2029–2031 Version 1 syllabuses. The 2026 update changes only a weblink; Cambridge reports no significant teaching changes for the 2027–2028 or 2029–2031 cycles. Exams are in the November series, and the qualification is not available in every administrative zone; confirm entry with your centre. Centre-selected local crop, weed, pest, disease and livestock examples must be checked against local agriculture. StudyForA does not replace supervised, risk-assessed practical work, the four assessed practical exercises, the individual practical investigation/report, teacher assessment or Cambridge moderation. Online practice is not an official mark or grade.
Before you begin
- Read the syllabus that matches your exam year and confirm your centre can enter you for code 0600. This route maps Cambridge's 2026 Version 2, 2027–2028 Version 1 and 2029–2031 Version 1 syllabuses. The 2026 update changes only a weblink; Cambridge reports no significant teaching changes for the 2027–2028 or 2029–2031 cycles. Exams are in the November series, and the qualification is not available in every administrative zone; confirm entry with your centre. Centre-selected local crop, weed, pest, disease and livestock examples must be checked against local agriculture. StudyForA does not replace supervised, risk-assessed practical work, the four assessed practical exercises, the individual practical investigation/report, teacher assessment or Cambridge moderation. Online practice is not an official mark or grade.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why should a crop disease be identified before choosing a treatment?
What you will learn
- Compare bacterial, fungal and viral infection pathways.
- Describe harmful effects and prevention/control for one locally selected disease from each group.
- Use local identification and avoid treating visual symptoms as a confirmed diagnosis.
Compare disease groups
Plant pathogens can enter or spread through infected seed or planting material, wounds, soil, water, wind-borne spores, insects or contact. The route varies by pathogen and crop.
Bacteria can multiply in plant tissues and may cause lesions or wilt; fungi produce hyphae and often spores; viruses reproduce inside living cells and may be moved by vectors or infected material. Symptoms can overlap, so diagnosis requires appropriate evidence.
Use named examples carefully
Examples include bacterial blight of rice, rice blast caused by a fungus, and cassava mosaic disease caused by viruses. The examples are not universal local priorities; a centre should select one locally important disease in each group.
For each selected disease, record how infection begins and spreads, the plant parts and yield affected, and prevention or control such as clean planting material, resistant varieties, field hygiene, vector management or locally approved treatment.
Build prevention around the pathway
Preventing infected planting material, reducing carry-over sources, monitoring symptoms and managing vectors can interrupt disease spread. Chemical controls, where appropriate, depend on diagnosis, crop, label and local expertise.
Do not recommend a pesticide from a symptom description alone. Consult a qualified crop-health specialist when diagnosis or control is uncertain.
Sources for this lesson
Pause and explain
Why should a crop disease be identified before choosing a treatment?
Worked example
A crop disease spreads from infected cuttings and is also moved between fields by an insect vector. Explain two interruption points.
Show the worked solution
- Use healthy, verified planting material to reduce introduction at planting.
- Monitor and manage the vector using locally approved integrated methods.
- Remove or manage infected sources only under suitable local plant-health advice and rules.
Answer Control can target both infected planting material and the vector pathway. The exact response depends on confirming the disease and local guidance.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare a bacterial disease spread through infected planting material with a fungal disease that produces wind-dispersed spores.
Give me a hint
Trace how each reaches a healthy plant and a matching prevention point.
Compare my reasoning
- Infected planting material can introduce bacteria directly into a field.
- Fungal spores can move from infected plants through the air to susceptible plants under suitable conditions.
- Clean material and monitoring address one pathway; locally appropriate resistance, hygiene or control may reduce the other.
The pathways differ, so prevention should target each one. The disease identity and local conditions determine suitable measures.
Look for these in your work
- Two pathways distinguished
- Controls linked to pathway
- Diagnosis remains essential
A learner chooses bacterial blight of rice, rice blast and cassava mosaic as examples. Explain why these are useful syllabus examples but not automatically suitable local case studies.
Give me a hint
Consider crop distribution, disease importance and local evidence.
Compare my reasoning
- The examples illustrate bacterial, fungal and viral disease groups.
- Their local prevalence and relevance vary with climate, crops and farming systems.
- Confirm local importance and accurate control details with the centre or regional plant-health service.
The examples help compare pathogen groups, but the syllabus requires locally appropriate named diseases. Centres should verify regional relevance and management.
Look for these in your work
- Groups distinguished
- Local variation recognised
- Verification source named
A farmer sees mosaic patterns on leaves and asks whether the crop has a virus. Explain a careful diagnostic response.
Give me a hint
Treat the pattern as evidence, not a confirmed diagnosis.
Compare my reasoning
- Record crop species, distribution of symptoms, recent conditions and affected plant parts.
- Check whether symptoms could also reflect nutrient, herbicide or environmental stress.
- Seek a qualified diagnostic service and follow local plant-health guidance before taking control action.
Mosaic symptoms may suggest a virus but are not proof. Confirm the cause before choosing a control, especially before applying chemicals or moving planting material.
Look for these in your work
- Observation separated from diagnosis
- Alternative causes considered
- Appropriate referral
Common mistakes
- Treating every leaf spot as fungal
- Confusing a vector with the pathogen itself
- Assuming symptoms alone identify a disease reliably
- Using a chemical without confirmed diagnosis or local approval
What can you explain now?
Why should a crop disease be identified before choosing a treatment?
Compare with the explanation
Different pathogens spread differently and need different controls
A control should interrupt the confirmed disease pathway.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Give one possible spread route for each pathogen group and explain why local diagnosis matters.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.