Lesson Notes By Weeks and Term v5 - Grade 11
Integrated pest, disease and weed management – Week 10 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Integrated pest, disease and weed management – Week 10 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Agricultural Management Practices
Class: Grade 11
Term: 3rd Term
Week: 10
Theme: General lesson support
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
In South Africa, agriculture is crucial for food security, job creation, and economic stability.
However, pests, diseases, and weeds pose a significant threat to crop yields and farm profitability. Farmers face challenges like the fall armyworm (a notorious pest), maize streak virus (a devastating disease), and invasive weed species that compete with crops for resources. Integrated Pest, Disease, and Weed Management (IPM) is a holistic approach that combines various strategies to minimize crop losses while minimizing environmental impact.
2. 1. What is Integrated Pest, Disease, and Weed Management (IPM)? IPM is a sustainable approach to managing pests, diseases, and weeds that minimizes economic, health, and environmental risks. It prioritizes preventative measures and considers all available control tactics, using chemical interventions only as a last resort. IPM aims to keep pest populations below economically damaging levels rather than eradicating them completely.
The core principles of IPM include: Prevention: Implementing practices that prevent pests, diseases, and weeds from becoming established.
Monitoring: Regularly scouting fields to identify pests, diseases, and weeds, and assessing their populations.
Thresholds: Determining the economic threshold (the pest density at which control measures are justified) and action threshold (the pest density at which control measures should be implemented to prevent reaching the economic threshold).
Multiple Tactics: Employing a variety of control methods, including cultural, biological, and chemical controls.
Evaluation: Assessing the effectiveness of control measures and adjusting the IPM plan as needed. 2.
2. Control Methods in IPM: IPM utilizes various control methods, broadly categorized into cultural, biological, and chemical control.
Cultural Control: These are preventative practices that modify the environment to make it less favorable for pests, diseases, and weeds.
Crop Rotation: Alternating crops can disrupt the life cycle of specific pests and diseases that rely on a single host plant.
Example:* Rotating maize with soybeans can help reduce the buildup of maize stalk borer populations.
Sanitation: Removing crop residues and weeds eliminates breeding grounds and overwintering sites for pests and diseases.
Example:* Removing infested tomato plants after harvest prevents the spread of early blight.
Tillage: Plowing or disking the soil can bury weed seeds and disrupt the life cycle of soilborne pests.
Example:* Deep plowing can bury weed seeds, preventing germination.
Resistant Varieties: Planting crop varieties that are resistant to specific pests and diseases reduces the need for other control measures.
Example:* Planting maize varieties resistant to maize streak virus.
Proper Irrigation and Fertilization: Maintaining optimal soil moisture and nutrient levels strengthens plants and makes them less susceptible to pests and diseases.
Example:* Avoiding over-irrigation can reduce the risk of fungal diseases.
Intercropping: Planting different crops together can reduce pest and disease incidence.
Example:* Intercropping maize with beans can reduce the incidence of stalk borer in maize.
Biological Control: Using natural enemies (predators, parasites, and pathogens) to suppress pest populations.
Predators: Insects or other animals that feed on pests.
Example:* Ladybugs feeding on aphids.
Parasites: Insects that lay their eggs in or on pests, eventually killing them.
Example:* Parasitic wasps attacking caterpillars.
Pathogens: Microorganisms (bacteria, fungi, viruses) that cause diseases in pests.
Example: Bacillus thuringiensis (Bt) bacteria used to control caterpillars.
Conservation Biological Control: Creating habitats that support natural enemies, such as planting flowering plants to provide nectar and pollen.
Example:* Planting indigenous flowers near crop fields to attract beneficial insects.
Augmentation Biological Control: Releasing natural enemies into the field to increase their populations.
Example:* Releasing commercially available ladybugs to control aphid outbreaks.
Chemical Control: Using pesticides to kill pests, diseases, or weeds. Chemical control should be used as a last resort in IPM, and pesticides should be selected carefully to minimize environmental impact and resistance development.
Selective Herbicides: Herbicides that target specific weed species while leaving the crop unharmed.
Example:* Using a herbicide that controls broadleaf weeds in a maize field without harming the maize plants.
Systemic Insecticides: Insecticides that are absorbed by the plant and kill pests that feed on it.
Example:* Applying a systemic insecticide to control aphids on citrus trees.
Contact Insecticides: Insecticides that kill pests upon direct contact.
Example:* Using a contact insecticide to control fruit flies on mangoes.
Fungicides: Chemicals used to control fungal diseases.
Example:* Applying a fungicide to prevent late blight on tomatoes.
Importance of Correct Application: Accurate dosage and timing of application are crucial for the effectiveness of chemical control and to minimize risks. Always follow label instructions. 2.
3. Monitoring and Record-Keeping: Regular monitoring of fields is essential for identifying pests, diseases, and weeds, and for assessing their populations. Accurate record-keeping is crucial for tracking pest trends, evaluating the effectiveness of control measures, and making informed decisions about IPM strategies.
A maize farmer in KwaZulu-Natal is experiencing an infestation of stalk borers. Scouting reveals an average of 2 stalk borers per plant. Research indicates that the economic threshold for stalk borers in maize is 5 stalk borers per plant. The farmer's action threshold is set at 3 stalk borers per plant. Since the current pest density (2 stalk borers per plant) is below the action threshold (3 stalk borers per plant), the farmer does not need to take immediate action.
However, continued monitoring is crucial to track the population and determine if intervention is needed later.
Guided Practice (With Solutions)
Question 1:
A tomato farmer in Limpopo is experiencing a severe outbreak of whiteflies. Describe three cultural control methods the farmer could implement to help manage the whitefly population.
Solution:
Crop Rotation: Avoid planting tomatoes in the same field year after year. Rotate with crops that are not hosts for whiteflies, such as legumes or grasses. This disrupts the whitefly life cycle.
Weed Control: Whiteflies can reproduce on weeds in and around the tomato field. Implement diligent weed control measures, including hand weeding, hoeing, and the use of appropriate herbicides, to eliminate weed hosts.
Reflective Mulch: Use reflective plastic mulch around the tomato plants. The reflective surface disorients whiteflies and reduces their ability to find the plants.