Use herbicides to reduce competition from weeds
Herbicides control weeds that compete with crop plants for resources such as light, water, mineral ions and space.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Know that crop and livestock production depend on both management and environmental conditions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a herbicide control in a crop field?
What you will learn
- Explain how herbicides reduce weed competition
- Distinguish herbicides from insecticides
Reduce competition with weeds
Herbicides are used to control unwanted plants such as weeds. Weeds can compete with crop plants for light, water, mineral ions and space. Reducing this competition can leave more resources available to the crop and support increased production.
The syllabus states that herbicides reduce competition with weeds. They do not remove every possible limit on crop growth; a crop still needs suitable water, nutrients, light and temperature.
Choose the correct control method
Identify the target organism before naming the control. Herbicides target weeds, which are plants. Insecticides target insect pests. Chemical fertilisers supply mineral ions. Mixing these terms leads to an incorrect explanation of how a yield may change.
An observation after herbicide use can show that weed growth or crop yield differed in the tested conditions. If the treatment changed several conditions at once, further controlled comparisons may be needed to isolate the reason.
Pause and explain
How can removing weeds help a crop?
Worked example
A crop grows among weeds that shade it and use soil water. Explain how a herbicide may support crop growth.
Show the worked solution
- The weeds compete for light and water.
- Herbicide reduces weed competition.
Answer By controlling weeds, a herbicide can reduce competition for light and water, leaving more of these resources available to the crop and potentially improving production.
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.
A weed and a crop grow close together. Name three resources for which they may compete.
Give me a hint
Think about what plants need for growth.
Compare my reasoning
- They can compete for light.
- They can compete for water and mineral ions.
They may compete for light, water and mineral ions; they may also compete for space.
Look for these in your work
- Three resources named
- Competition linked to both plants
A farmer applies an insecticide to control a field of weeds. Identify the mismatch and name the relevant treatment.
Give me a hint
Match each chemical type to its target.
Compare my reasoning
- Insecticides target insect pests.
- Herbicides control weeds.
The treatment does not match the target: an insecticide controls insects, while a herbicide is used to control weeds.
Look for these in your work
- Target classified
- Correct treatment named
A herbicide-treated plot has 18% weed cover rather than 42%, but crop yield is unchanged. Is this consistent with the purpose of the herbicide? Explain.
Give me a hint
Separate the target outcome from crop yield.
Compare my reasoning
- Weed cover decreased.
- Yield may be limited by other conditions.
Yes. The herbicide reduced weed cover and therefore weed competition. Crop yield may remain unchanged if another factor limited production or if the reduced competition did not alter the measured yield in this trial.
Look for these in your work
- Weed response identified
- Yield evidence interpreted cautiously
Common mistakes
- Calling a herbicide an insecticide
- Claiming weeds compete only for water
- Assuming weed control guarantees a higher yield
What can you explain now?
What does a herbicide control in a crop field?
Compare with the explanation
Weeds
These are unwanted plants.
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Make it stick
How do herbicides support crop plants, and how are herbicides different from insecticides?
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.