UNIT 13: Pests in Maize and Groundnuts

Success Criteria

• Identify major pests of maize and groundnut.
• Describe crop losses caused by pests.
• Describe pest control practices.
• Describe crop harvesting procedures.

Major Pests of Groundnuts

• Field Pests: Rats/mice, monkeys, crows, aphids, armyworms.
• Storage Pests: Termites, rats/mice.

1. Red Hairy Caterpillars

• Description: Larvae are reddish-brown with black bands on heads and abdomen, covered in hairs.
• Symptoms/Damage: Complete loss of leaves (eaten away), leaving only stems.
• Control:
  • Deep Ploughing.
  • Early planting.
  • Practicing crop rotation.
  • Planting trap crops.
  • Irrigating the soil.
  • Maintaining field hygiene.

2. Groundnut Leaf Miner

• Description: Shiny white eggs laid on the underside of leaves, producing green larvae with dark heads and thoraxes.
• Symptoms/Damage: Brown blotches on leaves, webbed leaves, plants appear burnt under severe conditions.
• Control:
  • Planting trap crops (e.g., soya beans).
  • Maintaining field hygiene.
  • Mulching with rice straws.
  • Intercropping.
  • Chemical control.

3. Gram Pod Borer

• Description: Lays spherical creamy-white eggs. Larvae are green or brown with dark brown-grey lines.
• Damage: Larva feeds on flowers and pods, causing holes in leaves.
• Control:
  • Deep Ploughing.
  • Practicing intercropping.
  • Applying insecticides.

4. Groundnut Aphids

• Damage: Wilting of tender leaves during dry conditions, stunted growth, spreading of rosette disease.
• Control:
  • Timely planting.
  • Correct spacing.
  • Handpicking and destruction.

5. Jassids (Empoasca kerri)

• Description: Green, wedge-shaped body.
• Symptoms: Chlorotic patches and whitening veins, crops appear yellow and scorched.
• Control:
  • Timely planting.
  • Practicing crop rotation.
  • Irrigating soil.
  • Chemical control.

6. Thrips (Scirothrips dorsalis)

• Description: Sucking insects with piercing mouthparts, yellow-black colored.
• Symptoms: Stunted growth, yellowish-green patches on the upper leaf.
• Control:
  • Spraying correct pesticides.

7. Termites (Odontotermes)

• Damage: Damage both maize and groundnuts in the field and storage; damage seeds, make holes into stems, cause plant lodging, eat roots.
• Control:
  • Destroy termite colonies.
  • Use well-decomposed manure.
  • Chemical control.
  • Frequent irrigation.
  • Seed treatment.

8. White Grubs (Holotrichia serrata)

• Symptoms/Damage: Eat roots, damage pods.
• Control:
  • Deep ploughing.
  • Using well-decomposed manure.
  • Timely planting.
  • Chemical control.
  • Seed treatment.

9. Pod Borer

• Symptoms/Damage: Holes in pods, excreta inside pods.
• Control:
  • Soil treatment (sterilization).
  • Chemical control.

Major Pests of Maize

• Field Pests: Stalk borer, armyworm, monkeys, mice, termites.
• Storage Pests: Weevils, locusts, rats/mice, termites.

1. Weevils (Sitophilus zeamais)

• Damage: Field/storage pest; pointed snout bores into grain and eats the embryo, reducing yield.
• Control:
  • Using recommended pesticides (e.g., Actellic dust for storage).
  • Timely harvesting.
  • Planting resistant varieties.

2. Rats/Mice

• Damage: Rodents with sharp teeth for gnawing, breaking, and chewing grains.
• Control:
  • Use of recommended chemicals (rodenticides).
  • Biological control (e.g., cats, owls).
  • Using rat traps to reduce population.

3. Armyworms (Spodoptera exempta)

• Damage: Move in large numbers, completely destroying leaves and whole plants.
• Control:
  • Using recommended pesticides (e.g., Carbaryl 85% wettable powder).

4. Maize Webworm (Cryptoblades gnidiella)

• Description: Long, dark brown larvae that form silken webs around cobs and flowers.
• Damage: Feed on leaves, flowers, and grains.
• Control:
  • Spraying with recommended chemicals.

5. Maize Aphids or Plant Lice (Rhopalosiphum maidis)

• Description: Soft, dark green insects that attack crops during dry conditions.
• Damage: Suck sap from green maize cobs and leaves, causing them to turn black.
• Control:
  • Early planting.
  • Spraying with recommended chemicals.

6. Stalk Borer (Sesamia calamistis)

• Damage: Bores into the stem, causing lodging and reduced photosynthesis.
• Control:
  • Ensuring field hygiene.
  • Spraying with recommended chemicals.
  • Destroying alternate hosts.

Losses Caused by Pests

Pests significantly impact crop production, leading to:

• Reduced Quantity: Direct damage to plants, reducing overall yield.
• Reduced Quality: Damage to produce makes it less marketable or unusable.
• Economic Losses: Due to lower yields, reduced quality, and increased production costs.
• Increased Production Costs: Due to expenditure on pesticides, labor for control, and other management practices.

Methods of Controlling Pests

1. Cultural Methods:

   • Early Planting: Allows crops to establish before peak pest populations.
   • Crop Rotation: Breaks pest life cycles.
   • Mulching: Can deter some pests or provide habitat for natural enemies.
   • Weed Control: Removes alternative host plants and hiding places for pests.
   • Field Hygiene: Removing crop residues and debris where pests may shelter or breed.
   • Closed Season: A period where certain crops are not grown to break pest (and disease) chains.
   • Proper Spacing: Improves air circulation and reduces humidity, making conditions less favorable for some pests.
   • Use of Resistant Seed Varieties: Planting varieties less susceptible to pest damage.

2. Mechanical or Physical Methods:

   • Flooding: Kills soil pests by suffocating them.
   • Trapping: Catching rodents and birds.
   • Hand Picking: Manual removal of visible pests (e.g., caterpillars).
   • Physical Barriers:
     • Erecting fences.
     • Making granaries (for storage pests).
     • Proper drying of produce.
     • Scarecrows (person-like figures).
     • Use of explosives or distress calls (recorded predator sounds) to scare off birds or monkeys.

3. Biological Methods:

   • Introduction of living organisms that destroy pests (e.g., ladybird beetles to control aphids; dogs to chase monkeys).

4. Legislative Procedures:

   • Laws and Policies: Used to prevent the introduction and spread of pests.
   • Quarantine: Isolating imported planting materials for observation; if diseased, destroyed; if disease-free, released.
   • Certification: Inspecting planting materials before distribution to farmers, certifying them as pest-free.
   • Notification Order: Publicizing information about certain pests through media.

5. Integrated Pest Management (IPM):

   • Description: A holistic approach integrating a range of practices for economic control of pests.
   • Processes:
     • Proper identification of the pest.
     • Learning about the pest and host life cycle.
     • Monitoring/sampling the environment for pest population levels.
     • Establishing action thresholds for control.
     • Staying updated on IPM developments.
     • Choosing an appropriate combination of management tactics (cultural, biological, chemical).

6. Chemical Methods:

   • Description: Application of pesticides (insecticides, rodenticides, nematicides).
   • Classification by Mode of Entry (Action):
     • Stomach Poisons: Enter pests through the mouth during feeding.
     • Contact Poisons: Kill pests upon direct contact.
     • Fumigants: Enter through the respiratory system.
     • Systemics: Applied to soil or plant, translocated throughout the plant; pests are poisoned when feeding.
   • Classification by Target Pests:
     • Insecticides (for insects).
     • Rodenticides (for rodents).
     • Nematicides (for nematodes).
   • Factors Affecting Efficiency:
     • Concentration of pesticides: Must be applied at correct concentrations.
     • Weather conditions: Apply during dry weather; rain washes away pesticides.
     • Timing of application: Most efficient when pests are highly susceptible.
     • Persistence: Pesticides with long residual effect are preferred.
     • Pest Resistance: Pests that develop resistance reduce efficiency.
   • Advantages:
     • Relatively fast.
     • Requires less labor for broad application.
   • Disadvantages:
     • Expensive.
     • Pollutes the environment.
     • Requires skill for mixing and application.
     • Can harm beneficial organisms.
     • Target pests may build resistance.

Crop Harvesting Procedures

Harvesting is done when crops are fully mature.

1. Harvesting Maize:

• Maturity Period: 120 to 160 days, depending on variety.
• Signs of Maturity:
  • Leaves and stalks turn brown.
  • Bending down/drooping of cobs.
  • Drying of tassels.
  • Grains make a rattling sound when a cob is shaken.
• Methods of Harvesting:
  • Picking cobs directly from standing stalks: Can be tiresome, some cobs may be left behind.
  • Cutting stalks and heaping (stooking): Stalks are cut and gathered into heaps or stooks for further drying, ensuring all cobs are harvested.

2. Harvesting Groundnuts:

• Maturity Period: 90 to 150 days, depending on variety (e.g., Chalimbana/Chitembana: 140-150 days; Malimba: 100-120 days; RG1/Mani-Pinta/Mawanga/CG7: 130-140 days; Nsinjiro: 120-140 days; Kakoma/Baka/Chitala: 90-100 days; Chalimbana 2005: 130-140 days).
• Signs of Maturity:
  • Pale brown color inside the pods.
  • Falling of leaves (though can also be a sign of leaf spot disease).
• Stages in Harvesting Groundnuts:
  • Lifting: Using hoes in heavy soils; hand pulling in light soils.
  • Drying: Plants are turned upside down and left in the sun for several days/weeks for thorough drying. Pods are then removed by hand.
  • Shelling: Removing covers or shells, either by hand or machines.
• Problems of Late Harvesting of Groundnuts:
  • Seeds may start germinating in the soil.
  • Pods may be left behind after harvesting.
  • Nuts can become contaminated before harvesting.
  • Nuts can be destroyed by late-season pests.

Factors Affecting Stage and Timing of Harvesting:

• Market demand.
• Prevailing weather conditions.
• Pest and disease outbreak.
• Intended use of the crop (e.g., for fresh consumption vs. storage).