Weeds and methods of weed control
Identify why weeds harm crops, how a named local weed spreads and how cultural, mechanical and chemical controls differ.
Section Component 2 · Practical Coursework preparation
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 weed be identified before selecting a control?
What you will learn
- Describe one locally named weed's effects and spread.
- Compare cultural, mechanical and chemical control methods and their limits.
Explain crop competition and spread
Weeds may compete for light, water, nutrients and space, interfere with harvest, host pests or contaminate produce. Their effect depends on crop stage, weed species and density.
Weeds spread through seeds or vegetative parts by wind, water, animals, planting material or equipment. The required named local species must be confirmed with the centre; do not assume the same weed is important in every region.
Match control to the weed and crop
Cultural control includes rotation, crop cover and timing that favours the crop; mechanical control includes hand removal or cultivation; chemical control uses herbicides selected for the crop, weed and local label.
Integrated control can combine methods. Timing, resistance, crop injury, environmental effects, cost and legal requirements matter. Chemical choice and use require qualified supervision and local rules.
Sources for this lesson
Pause and explain
Why should a weed be identified before selecting a control?
Worked example
A named weed produces seed before a field is harvested. Explain how it may spread and propose a non-chemical control to evaluate.
Show the worked solution
- Seeds may fall before harvest and later germinate; they can also move on contaminated equipment or with produce.
- Removing plants before seed set or using a suitable rotation can reduce replenishment, depending on the weed and crop.
- Verify the local species and evaluate timing, crop safety, labour and field conditions.
Answer Control should interrupt the weed's life cycle and fit the local crop. The exact method depends on correctly identifying the species.
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 one cultural and one mechanical method for reducing a locally identified weed.
Give me a hint
Explain the mechanism and one practical limitation of each.
Compare my reasoning
- Choose a cultural method such as rotation or crop cover that changes conditions for weed establishment.
- Choose a mechanical method such as timely removal or cultivation that removes or buries weeds.
- Check crop stage, weed life cycle, soil, labour, erosion risk and local guidance before selecting.
Cultural methods make the system less favourable to the weed; mechanical methods physically control it. Both depend on timing and crop and soil conditions.
Look for these in your work
- Methods classified correctly
- Mechanisms explained
- Limitations included
Explain why controlling a weed before seed set may reduce future weed pressure, and identify one reason this may not fully solve the problem.
Give me a hint
Consider seed banks, vegetative reproduction and movement from nearby fields.
Compare my reasoning
- Preventing seed production can reduce new seeds entering the soil seed bank.
- Existing seeds may remain viable, and some weeds spread by vegetative parts or arrive from neighbouring areas.
- Combine monitoring and repeated locally appropriate control, and record changes over time.
Preventing seed set can reduce future recruitment but does not remove existing seeds or all spread pathways.
Look for these in your work
- Seed-bank mechanism explained
- One remaining pathway identified
- Monitoring included
A herbicide appears less effective over several seasons. Give possible explanations and a safe next step.
Give me a hint
Do not recommend increasing a dose; consider identification, timing and resistance.
Compare my reasoning
- Check whether the weed was correctly identified and whether application timing and conditions matched the approved label.
- Consider resistance, poor coverage, rainfall timing or changes in the weed population.
- Stop and seek qualified local advice; review integrated cultural and mechanical options and follow current law and product labels.
Several causes are possible. Do not improvise a higher dose; verify the problem and use qualified, label-compliant local advice.
Look for these in your work
- Multiple causes considered
- Unsafe dose escalation avoided
- Appropriate local guidance requested
Common mistakes
- Calling any unwanted crop a weed without context
- Assuming hand removal is always safe or practical
- Using a herbicide without checking label, crop and local law
What can you explain now?
Why should a weed be identified before selecting a control?
Compare with the explanation
Different weeds spread and respond to control methods differently
Correct identification helps match control to the weed and crop.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain how a weed can harm a crop and distinguish cultural, mechanical and chemical control.
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.