WEEK 1: SS1 BIOLOGY THIRD TERM: RELEVANCE OF BIOLOGY TO AGRICULTURE

                                                 RELEVANCE OF BIOLOGY TO AGRICULTURE

I. Plant Classification Using Agricultural Techniques

Agricultural plant classification systems organize plants based on their utility, growing requirements, and management needs:

1. Food Crops vs. Non-Food Crops
• Food Crops: Grains, vegetables, fruits, nuts
• Non-Food Crops: Fiber plants, ornamentals, medicinal plants
2. Field Type Classification
• Field Crops: Grown on large scale (wheat, corn, soybeans)
• Horticultural Crops: Intensive management (vegetables, fruits)
• Plantation Crops: Perennial crops on large estates (tea, coffee, rubber)
3. Water Requirements
• Drought-resistant: Need minimal water (sorghum, millet)
• Water-intensive: Require regular irrigation (rice, sugarcane)
• Moderate: Average water needs (wheat, barley)
4. Nutritional Value
• Carbohydrate-rich: Grains, tubers
5. Harvesting Pattern
• Single harvest: Most grains
• Multiple harvest: Some vegetables
• Continuous harvest: Many fruits

II. Classification of Plants Based on Life Cycle

1. Annuals
• Complete life cycle in one growing season
• Examples: Corn, wheat, rice
2. Biennials
• Complete life cycle in two years
• Examples: Carrots, beets, cabbage
3. Perennials
1. Live for more than two years
2. Examples: Fruit trees, grapes, berries, alfalfa. 

 Effects of Agricultural Activities on Ecological Systems

1. Soil Impacts
• Soil erosion from tilling
• Compaction from heavy machinery
• Salinization from improper irrigation
• Nutrient depletion or accumulation
• Changes in soil microbiome
2. Water System Impacts
• Water table depletion
• Eutrophication from fertilizer runoff
• Contamination from pesticides
• Sedimentation in waterways
• Altered hydrological cycles
3. Biodiversity Impacts
• Habitat loss and fragmentation
• Reduction in native species
• Introduction of invasive species
• Disruption of pollinator populations
• Simplification of ecosystems
4. Atmospheric Impacts
• Greenhouse gas emissions (methane, CO₂, nitrous oxide)
• Particulate matter from burning crop residues
• Carbon sequestration potential of different practices
5. Positive Ecological Impacts of Sustainable Agriculture
• Agroforestry: Carbon sequestration and habitat creation
• Organic farming: Reduced chemical impacts
• Conservation agriculture: Soil preservation 

Crop Pests and Diseases: Identification, Impact, and Management

I. Definition of Crop Pests and Diseases

Crop Pests: Crop pests are organisms that damage crops, reducing yield and quality. They include insects, mites, rodents, birds, nematodes, and other animals that feed on or damage agricultural crops at various stages of growth and development.

A plant disease is defined as a departure or deviation of the crop plant from the normal state of health presenting marked symptoms or outward visible signs.

II. Types of Crop Pests and Classification of Insect Pests

Major Types of Crop Pests:

1. Insects: The most numerous and diverse group of pests
2. Mites: Tiny arachnids that feed on plant tissue
3. Nematodes: Microscopic worms that attack plant roots
4. Rodents: Mice, rats, and other small mammals
5. Birds: Some species that feed on seeds and fruits

Classification of Insect Pests:

Based on feeding habits:

1. Chewing insects: Caterpillars, grasshoppers, beetles
• Feed by biting and chewing plant parts
• Cause visible damage to leaves, stems, fruits
2. Sucking insects: Aphids, whiteflies, leafhoppers
• Feed by piercing plant tissue and sucking sap
• Cause wilting, yellowing, and stunted growth
3. Boring insects: Stem borers, fruit borers
• Tunnel into stems, fruits, or other plant parts
• Cause structural damage and wilting
4. Soil insects: Cutworms, wireworms, grubs
• Live in soil and attack underground plant parts
• Damage roots, tubers, and seedlings

III. Examples of Insect Pests, Crops Attacked, and Economic Importance

Insect Pest	Crops Attacked	Economic Importance
Aphids	Cereals, vegetables, fruits	Transmit viral diseases, reduce yield by 20-40%, affect quality of produce
Fall Armyworm (Spodoptera frugiperda)	Maize, rice, sorghum	Can cause 30-100% yield loss when severe, estimated $13 billion annual losses in Africa
Bollworms (Helicoverpa sp.)	Cotton, tomato, corn	Reduce yield by 20-60%, decrease quality, increased cost of pest control
Rice Stem Borer	Rice	Yield losses of 10-30%, major constraint in rice production
Fruit Flies	Mangoes, citrus, guava	Cause fruit drop, make fruits unmarketable, major quarantine concern limiting exports
Whiteflies	Vegetables, cotton, ornamentals	Vector for numerous plant viruses, reduce yield and quality
Locusts	Most field crops	Can devastate entire harvests during outbreaks, affecting food security

VI. Prevention and Control Measures of Crop Pests and Diseases

Cultural Control Methods:

1. Crop rotation: Growing different crops in succession to break pest and disease cycles
2. Sanitation: Removing crop residues, infected plants, and weeds that harbor pests and diseases
3. Tillage practices: Appropriate soil management to disrupt pest life cycles
4. Timing of planting: Avoiding peak pest/disease periods
5. Trap crops: Growing plants that attract pests away from main crop

Physical and Mechanical Control:

1. Handpicking: Manual removal of large pests
2. Trapping: Using various traps for monitoring and mass trapping
3. Barriers: Physical barriers like nets, fences, sticky bands
4. Heat treatment: For seeds and soil to kill pathogens
5. Pruning: Removing infected plant parts

Biological Control:

1. Beneficial insects: Introducing or conserving natural enemies (predators, parasitoids)
• Examples: Ladybugs for aphid control, Trichogramma wasps for caterpillar eggs
2. Microbial agents: Using beneficial fungi, bacteria, or viruses
• Examples: Bacillus thuringiensis (Bt) for caterpillars, Trichoderma for soil pathogens
3. Biopesticides: Plant-derived or naturally occurring substances
• Examples: Neem oil, pyrethrum, microbial pesticides

Chemical Control:

1. Insecticides: Control insect pests
• Contact, systemic, stomach poisons, growth regulators
2. Fungicides: Control fungal diseases
• Protective, curative, systemic types
3. Bactericides: Control bacterial diseases
4. Application methods: Spraying, dusting, seed treatment, soil application

ASSESSMENT: 

1. Define pests of crops and diseases of crops

2. State types of crop pests and classification of insect pests

3. Highlight examples of insect pest, crops attacked and economic importance

4. State the causes of crop diseases

5. Mention examples of crop diseases, causative organisms, method of transmission, symptoms and economic importance