A wheat farmer uses several methods to control weeds on the farm. The farmer grows wheat in rotation with legumes and root vegetables. (a) Name two cultural...
Question 1 Report
A wheat farmer uses several methods to control weeds on the farm. The farmer grows wheat in rotation with legumes and root vegetables.
(a) Name two cultural methods of weed control that the farmer could use on the wheat crop. [2]
(b) Describe how crop rotation helps to reduce weed problems on a farm. [3]
(c) Explain the difference between a pre-emergence herbicide and a post-emergence herbicide. [4]
(d) The farmer decides to apply a selective post-emergence herbicide to the wheat field. Describe the steps the farmer should follow to apply the herbicide safely and effectively. [4]
(e) Suggest two reasons why some farmers prefer to use cultural weed control methods rather than chemical herbicides. [2]
[Total: 15]
Answer Details
(a) Two cultural methods of weed control the wheat farmer could use (any two) [2]:
- Crop rotation
- Cultivation / ploughing / hoeing
- Mulching
- Hand weeding
- Close spacing of crop rows
- Use of cover crops
(b) How crop rotation helps reduce weed problems:
- Different crops in the rotation have different planting and harvesting dates, which disrupts the life cycle of weeds that are adapted to one particular crop's growing season [1].
- Different crops may require different cultivation practices (e.g. row spacing, tillage timing), preventing any one weed species from becoming dominant [1].
- Some crops in the rotation, such as legumes used as cover crops, can smother weeds by forming a dense canopy that blocks light from reaching the soil [1].
(c) The difference between pre-emergence and post-emergence herbicides:
| Feature | Pre-emergence herbicide | Post-emergence herbicide |
|---|---|---|
| Timing of application | Applied to the soil before weed seeds germinate / before the crop emerges [1] | Applied after weeds have emerged above the soil surface / sprayed onto actively growing weeds [1] |
| How it works | Forms a chemical barrier in the soil that kills weed seedlings as they begin to grow [1] | Absorbed through the leaves and translocated within the weed plant to kill it [1] |
(d) Steps to apply a selective post-emergence herbicide safely and effectively:
- Read the product label to check the correct application rate and any crop-specific instructions for wheat [1].
- Mix the herbicide with water in a sprayer at the recommended dilution rate [1].
- Apply the spray evenly across the field in calm weather conditions (low wind) to avoid drift onto neighbouring areas or water courses [1].
- Wear protective clothing including gloves, face mask, and overalls during mixing and application to prevent exposure [1].
(e) Two reasons why some farmers prefer cultural weed control over chemical herbicides (any two) [2]:
- Cultural methods do not involve purchasing expensive chemicals, so they reduce input costs [1].
- Cultural methods avoid the risk of chemical residues contaminating the soil or water sources [1].
Other valid reasons: cultural methods do not contribute to the development of herbicide-resistant weed populations; cultural methods are more suitable for organic farming systems where chemical herbicides are not permitted.
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