Pests and Diseases

Pests are organisms that cause harm to humans, livestock, and crops by inflicting physical damage. These can be plants or animals, with plant pests commonly referred to as weeds. Pests are significant due to their adverse effects on agriculture, livestock production, and overall human activity.

Crop pests specifically target agricultural produce that is vital to humans.

Classification of Pests

Pests can be classified based on the part of the crop plant they attack:

• Stem Borers: Larvae of certain moths that bore into maize stems, weakening them and causing breakage.
• Root Feeders: Insects like larvae or adults that burrow into the soil and feed on root crops such as yam, causing damage.
• Leaf Feeders: Pests like snails, beetles, and grasshoppers feed on leaves, reducing plant growth.
• Young Shoot Feeders: Aphids, mealybugs, and scale insects extract sap from young shoots, sometimes transmitting diseases like Cassava Leaf Mosaic Virus.
• Fruits and Seed Feeders: Pests such as moths, fruit flies, and beetles attack fruits and seeds, leading to crop losses.

Examples of Pests

• Insects like flies and aphids
• Mites and ticks
• Birds
• Flatworms
• Tapeworms
• Snails
• Protozoa
• Rodents

Life Cycle of Pests

Most insect pests undergo a life cycle with four stages: egg, larva, pupa, and adult. The larval and adult stages are typically responsible for significant crop damage. Insects may have complete or incomplete life cycles.

Grasshopper Life Cycle

Grasshoppers undergo incomplete metamorphosis with three stages: egg, nymph, and adult. Fertilization is internal, requiring male and female mating.

Egg Stage

The female lays eggs in a shallow hole, covering them with a sticky substance that hardens to form an egg pod. Each pod contains 10-200 eggs, which remain dormant during winter and hatch in warmer weather.

Nymph Stage

Nymphs feed on soft plant foliage and resemble smaller, wingless adults. They molt 3-6 times, growing larger and developing wing pads before reaching adulthood in 25-30 days.

Adult Stage

Adult grasshoppers reach sexual maturity in about 15 days, completing the life cycle.

Effects of Grasshoppers on Cassava

Both nymphs and adults feed on cassava leaves, shoots, and bark, reducing the plant's photosynthesis ability and significantly lowering crop yield.

Cassava Mealybug Life Cycle

Female mealybugs lay eggs through parthenogenesis (without fertilization). The eggs hatch into larvae, which are carried by wind or transported via cassava stem cuttings. The larvae undergo three molts to become adults, completing their life cycle in about 21 days. Adults live for approximately 145 days.

Effects of Cassava Mealybug

• They suck plant sap, stunting shoot growth.
• Cause bunchy tops on shoots.
• Lead to leaf death and defoliation.
• Disrupt photosynthesis.

Yam Beetle Life Cycle

Yam beetles mate between November and December in riverine areas. Fertilized eggs hatch into larvae, which feed on decaying organic matter. Larvae molt three times to become pupae, which then develop into adults. Between April and June, adult beetles feed on yam tubers, causing damage. They migrate back to riverine areas for mating between October and November.

Effects of Yam Beetles

• Adult beetles severely damage yam tubers, making them unusable.
• Early attacks significantly reduce crop yields.

Pest Control

Pest control involves managing and reducing pest populations to protect crops and livestock, thereby improving food production.

Objectives of Pest Control

• Reduce pest populations.
• Safeguard crops from damage.

Understanding pests' life cycles and habits is essential for effective pest control, focusing on:

• Peak attack periods
• Resting stages after attacks
• Vulnerable stages for control

Methods of Pest Control

• Physical Methods: Manually removing pests, using traps, or methods like burning or flooding. Effective for large pests but labor-intensive.
• Cultural Methods: Adopting farming practices such as crop rotation, mixed cropping, and adjusting planting times to create unfavorable conditions for pests.
• Biological Methods: Introducing natural predators, parasites, or using plant-based extracts to control pest populations. Cost-effective and long-lasting.
• Chemical Methods: Using pesticides like insecticides and herbicides to eliminate pests. While effective, these methods may harm the environment and health.

Economic Importance of Pests

• Lower farmers' income and increase production costs.
• Reduce crop yield and quality.
• Damage plants through feeding activities.
• Act as vectors for diseases.
• Cause unattractive and unmarketable produce.
• Reduce viability of stored farm produce.

Crop Pests

Animal Pests

Diseases

A disease is any alteration in the normal health of plants or animals, often marked by visible symptoms or changes. Diseases result from physical, chemical, or biological factors, and their causative agents are referred to as pathogens.

Pathogens include bacteria, viruses, fungi, nematodes, and protozoa. Insects and rodents, known as vectors, often transmit these pathogens, contributing to the spread of diseases. Some crop diseases may also arise due to nutrient deficiencies.

1) Maize Smut

Caused by: Fungus (Ustilago maydis)

Transmission:

• Airborne spores
• Spores deposited on fruits

Symptoms:

• Lower yield
• Formation of galls on ears, leaves, and tassels, which turn black

Control Measures:

• Remove and destroy infected plants
• Plant resistant varieties
• Treat seeds before planting

2) Cassava Mosaic

Caused by: Virus

Transmission:

• Infected cuttings
• Whiteflies (piercing and sucking insects)

Symptoms:

• Mottled leaves with a mosaic pattern
• Stunted growth
• Distorted stems and leaves
• Reduced yield

Control Measures:

• Remove and burn infected plants
• Maintain clean farming practices
• Plant disease-resistant varieties
• Spray insecticides
• Use healthy, disease-free cuttings

3) Cocoa Swollen Shoot

Caused by: Virus

Transmission:

• Infected budwood
• Mealybugs

Symptoms:

• Swelling of stems and roots
• Yellowing of leaves (chlorosis)

4) Rice Blight

Caused by: Fungus (Pyricularia oryzae)

Transmission:

• Airborne spores
• Spores landing on leaves

Symptoms:

• Small red spots on leaves turning grey or brown
• Reduced yield

Control Measures:

• Avoid overuse of nitrogen fertilizers
• Plant resistant varieties
• Use clean, disease-free seeds
• Apply fungicides

5) Groundnut Rosette

Caused by: Virus

Transmission: Aphids (piercing and sucking insects)

Symptoms:

• Yellow leaves with mottling
• Stunted growth with curled leaves
• Shortened internodes
• Plant wilting and death

Control Measures:

• Plant early
• Apply insecticides
• Practice crop rotation
• Plant resistant varieties
• Remove and burn infected plants

6) Maize Rust

Caused by: Fungus (Puccinia sorghi)

Transmission:

• Airborne spores
• Spores landing on leaves

Symptoms:

• Cobs and grains covered in black spores
• Premature plant death

Control Measures:

• Apply fungicides before planting
• Plant resistant varieties
• Plant early in the season

7) Coffee Leaf Rust

Caused by: Fungus (Hemileia vastatrix)

Transmission:

• Wind
• Rain splash

Symptoms:

• Yellow or brown spots on leaves
• Leaf drop
• Orange powdery mass on leaf surfaces
• Reduced yield

Control Measures:

• Use resistant varieties
• Plant seeds from healthy plants
• Spray with copper-based fungicides

8) Root Knot (Tomato/Okra)

Caused by: Nematodes

Transmission: Nematodes in the soil

Symptoms:

• Knots or galls on roots
• Stunted growth
• Reduced yield

Control Measures:

• Practice crop rotation
• Plant resistant varieties

9) Leaf Blight of Cassava

Caused by: Bacteria (Xanthomonas manihotis)

Transmission:

• Insects
• Rain splash
• Infected cuttings
• Contaminated tools

Symptoms:

• Blighted leaves
• Wilting and leaf drop
• Stem die-back
• Canker formation on stems
• Reduced yield

Control Measures:

• Plant resistant varieties
• Rotate crops
• Plant early
• Use disease-free cuttings

10) Rice Blast

Causative Organism: Fungus (Magnaporthe oryzae)

Method of Transmission:

• Spores spread by wind
• Contaminated irrigation water

Symptoms:

• Brown spots on leaves
• Drying of leaves

Prevention and Control Measures:

• Plant resistant varieties
• Apply fungicides

11) Cocoa Black Pod

Causative Organism: Fungus (Phytophthora palmivora/Phytophthora megakarya)

Method of Transmission: Sporangia or zoospores spread via water, ants, and other insects

Symptoms:

• Brown patches on pods
• Pods turning black and drying up

Prevention and Control Measures:

• Use fungicides
• Remove and burn infected pods

Animal Diseases

Effects/Economic Importance of Diseases

• Damage to crops reduces growth and yield.
• Death of crops and animals affects food security.
• Reduces farmers' income and profitability.
• Causes poor health and restlessness in animals.
• Severe outbreaks can devastate livestock populations.

General Methods of Disease Control

• Maintain proper sanitation by regularly cleaning feeding areas and disinfecting pens.
• Quarantine new animals before introducing them to existing stock.
• Adopt good stock management practices, including proper feeding and rotational grazing.
• Vaccinate animals to prevent diseases.

Measures for Infection Outbreaks

When an infection occurs, it can be managed through the following steps:

• Separate sick animals from healthy ones.
• Restrict movement of animals and animal products in and out of the farm.
• Ban visitors from entering the farm.
• Avoid grazing animals in common areas.
• Conduct containment vaccination.
• Install disinfectant foot dips at farm entrances.
• Ensure strict sanitation and hygiene.

Quarantine and Isolation

Quarantine

Quarantine is the separation of animals, especially new ones, that may have been exposed to infectious diseases, keeping them away from healthy stock.

The purpose of quarantine is to observe animals for signs of diseases during the incubation period. For example, rabies requires six months of quarantine, while most other diseases require 30 days.

Quarantine Procedures

• Screen animals for parasites through fecal examination during the quarantine period.
• De-worm animals on the 23rd or 24th day if necessary.
• Dip or spray animals on the 25th or 26th day to eliminate ectoparasites.

Isolation

Isolation refers to separating animals that are infected or suspected of having a contagious disease from healthy ones to prevent the spread of infection.

Guidelines for Isolation

• Place isolated animals in a dedicated isolation ward located far from healthy livestock.
• If no isolation ward is available, keep isolated animals at the far end of the animal housing, as far as possible from healthy animals.
• Avoid using the same equipment for both isolated and healthy animals.
• Thoroughly disinfect all equipment used for isolated animals after each use.
• Reintroduce isolated animals to the herd only after they have fully recovered and the outbreak is contained.