Pests of Crops

Pests of Crops

Pests are a significant threat to agricultural productivity, damaging crops and reducing yields. This note provides an overview of pests of crops, including definitions, classifications, and the most important insect and non-insect pests. It also covers control measures, side effects, and the economic impact of pests.

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2. Pests of Crops

(a) Meaning of Pests

Definition: Pests are organisms that cause harm to crops, leading to reduced growth, yield, and quality. These organisms can include insects, rodents, birds, fungi, bacteria, and even weeds.

Key Points:

• Pests are organisms that damage plants, reduce crop yield, and affect food quality.
• They compete with crops for nutrients, water, and light, and may directly damage plant tissues or carry diseases.
• Pests are categorized as either biological pests (living organisms) or physical pests (e.g., temperature extremes or soil conditions).

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(b) Classification of Pests

Pests are broadly classified into two categories:

1. Insect-Pests:
   • These are insects that harm crops by feeding on them or transmitting diseases.
2. Non-Insect Pests:
   • These include organisms like rodents, birds, and other animals that damage crops.

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(c) Classification of Insect-Pests Based on Mouth Parts

Insects can be classified according to their mouthparts and feeding habits. The three main categories are:

(i) Biting and Chewing Insects

• Characteristics: These pests have mandibles that allow them to chew and destroy plant tissues.
• Examples:
  • Locusts: Known for their destructive feeding habits on leaves and crops.
  • Caterpillars (e.g., armyworms): Consume leaves, stems, and flowers.

(ii) Piercing and Sucking Insects

• Characteristics: These insects have needle-like mouthparts to pierce plant tissues and suck out sap or fluids.
• Examples:
  • Aphids: Suck sap from leaves and stems, weakening plants.
  • Whiteflies: Similar to aphids, they feed on plant sap and cause stunting.

(iii) Boring Insects

• Characteristics: These pests create tunnels or bore into plant tissues, causing physical damage.
• Examples:
  • Stem Borers: Such as the maize borer, which damages the stem of crops like maize.
  • Woodboring Beetles: These insects create holes in woody plants and crops.

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(d) Important Insect-Pests of Major Crops

(i) Cereals

• Stem Borer:

  • Life Cycle: Eggs are laid on leaves. The larvae burrow into stems, causing internal damage.
  • Economic Importance: Major pest of maize and rice, causing yield losses.
  • Damage: Weakens stems, leading to lodging (falling over) and reduced grain production.
  • Control: Use of resistant varieties, biological control, and proper crop management.

• Armyworm:

  • Life Cycle: Eggs hatch into larvae that feed on leaves and young plants.
  • Economic Importance: Affects maize, sorghum, and other cereals.
  • Damage: Defoliation, reducing crop photosynthesis and yields.
  • Control: Insecticides, crop rotation, and early detection.

• Earworm:

  • Life Cycle: Larvae feed on kernels, often entering ears of maize.
  • Economic Importance: Causes direct damage to maize and other cereals.
  • Damage: Reduced grain quality, leading to market losses.
  • Control: Pesticide application, monitoring, and proper harvesting practices.

(ii) Legumes

• Pod Borer:

  • Life Cycle: Eggs are laid on flowers; larvae bore into pods.
  • Economic Importance: Major pest of beans and cowpeas.
  • Damage: Infestation causes pod damage and seed loss.
  • Control: Insecticides, cultural practices, and crop rotation.

• Aphids:

  • Life Cycle: Reproduce rapidly by asexual reproduction (parthenogenesis).
  • Economic Importance: Suck sap from leaves and transmit viruses.
  • Damage: Yellowing, stunted growth, and disease transmission.
  • Control: Natural predators (ladybirds), neem oil, and resistant varieties.

• Sucking Bugs:

  • Life Cycle: Adults and nymphs suck sap from plant tissues.
  • Economic Importance: Major pest of legumes like cowpeas and soybeans.
  • Damage: Deformation of pods and reduced yields.
  • Control: Insecticides, biological control, and integrated pest management (IPM).

(iii) Beverages

• Cocoa Myrids (Capsids):
  • Life Cycle: Eggs are laid on cocoa pods. Nymphs and adults feed on the pods, causing damage.
  • Economic Importance: Affects cocoa trees, leading to yield losses.
  • Damage: Infected pods turn yellow, reducing quality.
  • Control: Pruning, pesticide application, and controlling vector populations.

(iv) Tubers

• Yam Beetle:

  • Life Cycle: Larvae burrow into yam tubers, causing direct damage.
  • Economic Importance: Major pest of yam crops.
  • Damage: Tuber rot, reducing marketability.
  • Control: Soil insecticides and crop rotation.

• Cassava Mealybugs:

  • Life Cycle: Feed on sap, causing stunted growth.
  • Economic Importance: Affects cassava crops, reducing yields.
  • Damage: Deformation of leaves and tubers.
  • Control: Use of resistant varieties and natural predators.

• Green Spider Mites:

  • Life Cycle: Suck sap from plant tissues, leading to leaf damage.
  • Economic Importance: Affects cassava, sweet potato, and other tubers.
  • Damage: Leaf discoloration and weakening of plants.
  • Control: Miticides and biological control.

• Variegated Grasshopper:

  • Life Cycle: Feed on crops, especially young seedlings.
  • Economic Importance: Damages tubers and crops like cassava and sweet potatoes.
  • Damage: Defoliation and stunted growth.
  • Control: Insecticides and physical barriers.

(v) Fibre

• Cotton Stainer:

  • Life Cycle: Suck sap from cotton plants, causing staining of cotton fibers.
  • Economic Importance: Major pest in cotton farming.
  • Damage: Reduces cotton fiber quality.
  • Control: Use of insecticides and resistant cotton varieties.

• Bollworms:

  • Life Cycle: Larvae burrow into cotton bolls, damaging fibers.
  • Economic Importance: Major cotton pest.
  • Damage: Reduced cotton yield and quality.
  • Control: Pesticide application and monitoring.

(vi) Fruits and Vegetables

• Thrips:

  • Life Cycle: Feed on leaves and flowers, causing deformed fruits.
  • Economic Importance: Affects various fruits and vegetables.
  • Damage: Deformation and reduced marketability.
  • Control: Use of insecticides and resistant crops.

• Grasshopper:

  • Life Cycle: Adults and nymphs feed on leaves, flowers, and fruits.
  • Economic Importance: Causes damage to vegetables and fruits.
  • Damage: Defoliation and reduced yields.
  • Control: Biological control and insecticides.

• Leaf Roller:

  • Life Cycle: Larvae feed inside rolled leaves, causing damage to plant tissues.
  • Economic Importance: Damages vegetables like cabbage and lettuce.
  • Damage: Reduced yield and quality.
  • Control: Use of insecticides and traps.

• Leaf Beetle:

  • Life Cycle: Adults and larvae feed on leaves and stems.
  • Economic Importance: Affects leafy vegetables and fruits.
  • Damage: Holes in leaves and reduced photosynthesis.
  • Control: Insecticides and crop rotation.

• Scale Insect:

  • Life Cycle: Feed on plant sap, causing yellowing and stunting.
  • Economic Importance: Affects citrus and other fruit crops.
  • Damage: Yellowing of leaves and reduced fruit production.
  • Control: Biological control and horticultural oils.

(vii) Stored Produce

• Grain Weevils:

  • Life Cycle: Infest stored grains, feeding on kernels.
  • Economic Importance: Major pest of stored cereals like wheat and maize.
  • Damage: Grain loss and contamination.
  • Control: Use of sealed storage and grain fumigation.

• Bean Beetle:

  • Life Cycle: Feed on dried beans in storage.
  • Economic Importance: Causes damage to stored beans.
  • Damage: Reduces the quality and marketability of beans.
  • Control: Proper storage and pest monitoring.

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(e) Non-Insect Pests

Examples:

• Rodents: Rats and mice damage crops by feeding on seeds and tubers.
• Birds: Birds like pigeons and sparrows feed on seeds and fruit, causing significant losses in crops like rice and maize.

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(f) Side Effects of Preventive and Control Methods

(i) Chemical Control

• Side Effects: Pollution, poisoning, and resistance buildup in pests.
• Example: Overuse of insecticides can lead to environmental pollution and harm beneficial insects (e.g., bees).

(ii) Biological Control

• Side Effects: Disruption of the ecosystem, especially if introduced species become invasive.
• Example: Introduction of a predator species to control pests might affect non-target species.

(iii) Cultural Control

• Side Effects: Harmful effects of practices like burning, which can degrade soil quality and biodiversity.
• Example: Frequent burning can deplete organic matter in the soil, reducing its fertility.

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(g) General Effects/Economic Importance of Pests

Key Points:

• Pests can cause significant yield losses, affecting food security.
• They also contribute to crop diseases, further reducing productivity.
• The cost of pest control measures is a significant economic burden for farmers.

Economic Importance:

• Loss of marketable crops.
• Increased cost of production due to control measures.
• Damage to the environment through overuse of chemical control methods.