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What is Scale on Plants?

Published in Plant Pests 3 mins read

Scale on plants refers to small, sap-sucking insects that appear as bumps or encrustations on leaves, stems, and petioles, often resembling scales. These insects feed on plant juices, weakening the plant and potentially causing significant damage.

Understanding Scale Insects

Scale insects are a common pest affecting a wide variety of indoor and outdoor plants. They are characterized by their protective outer covering, which gives them their "scale-like" appearance. This covering shields them from many insecticides, making them challenging to control.

Types of Scale

There are two main types of scale insects:

  • Armored Scale: These scales have a hard, waxy covering that is separate from their body. They feed by inserting their stylet (a needle-like mouthpart) into the plant tissue and sucking out sap. The covering is made of wax and shed skins.

  • Soft Scale: Soft scales secrete a waxy coating that is attached to their body. They also suck plant sap but excrete a sticky substance called honeydew.

Identifying Scale Infestation

Identifying a scale infestation early is crucial for effective control. Look for the following signs:

  • Small, raised bumps on leaves, stems, and petioles. They can be various colors, including brown, white, or gray.
  • Sticky honeydew on the plant or surrounding surfaces. Honeydew can attract ants and promote the growth of sooty mold.
  • Yellowing leaves or stunted growth.
  • Reduced plant vigor.
  • Ants frequently visiting the plant (they feed on the honeydew produced by soft scales).

Damage Caused by Scale

Scale insects cause damage by:

  • Sucking plant sap: This weakens the plant, leading to yellowing leaves, stunted growth, and reduced vigor.
  • Injecting toxins: Some scales inject toxins into the plant while feeding, further damaging the plant tissue.
  • Producing honeydew: Honeydew attracts ants and promotes the growth of sooty mold, which can block sunlight and hinder photosynthesis.

Controlling Scale Infestations

Controlling scale can be challenging due to their protective covering. Here are several methods:

  • Manual Removal: For small infestations, manually remove the scales by scraping them off with your fingernail or a soft brush.

  • Insecticidal Soap or Horticultural Oil: These products can smother the scales, but repeat applications are usually necessary. Be sure to follow the label instructions carefully.

  • Systemic Insecticides: These insecticides are absorbed by the plant and kill the scales as they feed. They are typically used for severe infestations. Always use systemic insecticides according to the label, and be aware of any risks to beneficial insects or the environment.

  • Biological Control: Introduce natural enemies of scale insects, such as ladybugs, lacewings, or parasitic wasps.

  • Pruning: Heavily infested branches should be pruned and disposed of properly.

Prevention

Preventing scale infestations is always better than treating them. Here are some tips:

  • Inspect new plants before bringing them home.
  • Maintain healthy plants by providing proper watering, fertilization, and light.
  • Regularly inspect your plants for signs of scale or other pests.
  • Control ant populations, as they can protect scales from natural enemies.

Scale insects are a common plant pest that can cause significant damage if left unchecked. Early detection and appropriate control measures are essential for maintaining healthy plants.