Crop Production — Crop Protection: Weed Control

Subject: Agriculture | Level: Form 2 / Age ~15 | Context: Kenya

Specific learning outcomes

1. Identify weeds in a crop field by appearance and effects on crops.
2. Classify weeds using simple criteria (life cycle, form, habitat, and parasitism).
3. Examine and explain various methods of weed control and when to use them.
4. Carry out weed control safely using appropriate methods (practical skills).
5. Appreciate the economic importance of weeds to a farming household and make simple cost–benefit decisions.

1. Identifying weeds in the field

Look for plants that compete with the crop for light, nutrients or water, reduce yield, or transmit pests and diseases. Note growth pattern, leaf shape, flowers and root type.

2. Classifying weeds (useful criteria)

Classify weeds so you can choose the best control method.

• By life cycle: Annual, biennial, perennial.
• By form (habit): Grasses, broadleaves (forbs), sedges.
• By habitat: Upland/field, aquatic, disturbed ground.
• By effect on crop: Parasitic (e.g., Striga) vs non-parasitic.
• By origin: Native vs invasive (e.g., Parthenium is invasive in many areas).

3. Methods of weed control

Choose methods based on weed type, crop stage and farm resources. Integrate several methods for better results.

4. Integrated Weed Management (IWM)

IWM means combining methods: cultural + mechanical + chemical + biological. Plan control at different crop stages and use monitoring (weed counts) to decide action.

5. How to carry out weed control (practical steps)

6. Economic importance of weeds to a farming household

Weeds have mainly negative effects on crop production but can also have small benefits. Farmers must decide whether control costs are worth the yield gains.

• Costs caused by weeds: lower yields, higher labour and input costs, decreased crop quality, pest and disease hosts.
• Control costs: labour for weeding, cost of herbicides and equipment, training and PPE costs.
• Small benefits: some weeds are edible, used as fodder or medicines, and can protect soil from erosion if managed carefully.
• Simple farm decision: Do a basic cost–benefit — estimate expected yield loss without control vs cost of control method.

Suggested learning experiences (classroom & field)

1. Field trip: visit a nearby smallholder farm or school demonstration plot. Identify 8 common weeds and photograph/sketch them.
2. Group activity: classify collected weed samples into grasses, broadleaves and sedges and by life cycle.
3. Demonstration: teacher or extension officer shows correct hoeing technique and safe herbicide mixing (no student handles herbicide unsupervised).
4. Role play: one group acts as farmers proposing control plans, another group acts as extension officers giving advice — include costs.
5. Practical: design a simple weed control plan for a small maize plot (timing, methods, costs) and present to class.
6. Calculation exercise: estimate yield gain from weeding vs labour cost to practice economic judgment.

Assessment / short tasks

• Short quiz: name 4 common weeds in Kenyan fields and state one control method for each.
• Practical test: demonstrate correct hoeing of a 2 m x 2 m sample plot and remove weeds properly.
• Worksheet: classify given weed pictures and recommend control (cultural, mechanical, chemical, or integrated).
• Homework: prepare a one-page cost–benefit plan to control Striga in a 0.25 ha maize plot using push–pull and/or other methods.

Safety and environmental notes

• Never spray herbicides near wells or flowing water. Protect pollinators by avoiding flowering weeds at time of spraying.
• Use herbicides only when necessary; prefer cultural and mechanical control where practical.
• Dispose empty chemical containers at designated take-back or puncture and bury away from water sources if no scheme exists (follow national rules).
• Train farm workers in safe handling and first aid for chemical exposure.

Mapping activities to learning outcomes

• a) Identify weeds — field trip + identification quiz.
• b) Classify weeds — sample sorting and worksheet.
• c) Examine methods — class discussion, demonstrations & poster work.
• d) Carry out control — supervised practical weeding and plan design.
• e) Appreciate economics — cost–benefit homework and role play.

Prepared for Kenyan school context — encourage involvement of local extension officers for demonstrations and safe herbicide use. For more local specifics (approved herbicides, container disposal points), check Ministry of Agriculture or local extension services.