PHC Insect and Disease Control

PHC for Insect and Disease Control

In addition to the above treatment options for restoration and maintenance of your trees and shrubs, there are basic elements that influence plant health which include sufficient water and light, and a proper balance of nutrients. Too much or too little of any of these environmental conditions may cause plant stress.

Environmental stress weakens plants and makes them more susceptible to insect and disease attack.

Trees deal with environmental stresses, such as shading and competition for water and nutrients in their native environment by adjusting their growth and development patterns to reflect the availability of the resources. Although trees are adapted to living in stressful conditions in nature, many times the stresses they experience in the landscape are more than they can handle and may make them more susceptible to insects and diseases.



Three things are required for a disease to develop:

  • the presence of a pathogen (the disease-causing agent)
  • plant susceptibility to that particular pathogen
  • an environment suitable for disease development

Plants vary in susceptibility to pathogens. Many disease-prevention programs focus on the use of pathogen-resistant plant varieties. Even if the pathogen is present and a susceptible plant host is available, the proper environmental conditions must be present over the correct period of time for the pathogen to infect the plant.

Diseases can be classified into two broad categories: those caused by infectious or living agents (diseases) and those caused by noninfectious or nonliving agents (disorders).




Some insects can cause injury and damage to trees and shrubs. By defoliating trees or sucking their sap, insects can retard plant growth. By boring into the trunk and branches, they interfere with sap flow and weaken the tree structure. Insects may also carry some plant diseases. In many cases, however, the insect problem is secondary to problems brought on by a stress disorder or pathogen.

It is important to remember that most insects are beneficial rather than destructive. They help with pollination or act as predators of more harmful species. Therefore, killing all insects without regard to their kind and function can actually be detrimental to tree health.

Insects may be divided into three categories according to their method of feeding: chewing, sucking, or boring. Insects from each group have characteristic patterns of damage that will help you determine the culprit and the proper treatment. Always consult a tree care expert if you have any doubt about the nature of the insect problem or the proper treatment.

Chewing insects

  • Eat plant tissue such as leaves, flowers, buds, roots, and twigs.
  • Chewing insects include beetle adults or larvae, moth larvae (caterpillars), and many other groups of insects.
  • The damage they cause (leaf notching, leaf mining, leaf skeletonizing, etc.) will help in identifying the pest insect.

Sucking insects

  • Feed on the plant’s juices such as sap.
  • Some examples of sucking insects are aphids, mealy bugs, thrips, and leafhoppers.
  • Damage caused by these pests is often indicated by discoloration, drooping, wilting, leaf spots (stippling), honeydew, or general lack of vitality in the affected plant.?


Boring insects

  • Spend time feeding beneath the bark of a tree as larvae.

Insects Commonly Found on Ornamental Trees and Shrubs


  • Found on azaleas
  • Can cause discoloration and lack of vigor
  • Generally don't kill the shrub
  • Bugs are located on the underside of the leaf    
  • Hatches in spring. Most active during summer months control
  • Preventative treatments are most effective in the spring and should continue through the summer


  • Found on junipers, cedars, arborvitae and white pine
  • Bagworm caterpillars make distinctive 1.5 to 2 inch long spindle-shaped bags.
  • If the plant is already infested – treat  immediately
  • Treat  while the larvae are still small (less than 1/2-inch long)control -The best time to treat  is usually in June/July. Apply (2) treatments of insecticide


  • Found on gardenia, hawthorn, holly, ornamental pear, pyracantha, and laurel
  • Damages plants by sucking out large amounts of sap and secrets honeydew causing sooty moldcontrol
  • Foliar treatments are best applied at the crawler stage
  • Apply a Spring horticulture oil / Safari treatment during 45 - 70 degree weather (March/April) then repeat mid-August?

Aphids/White Flies

  • Mostly affects hollies
  • Identified by Sooty mold
  • A black fungi caused by the droppings also known as honeydew. control
    • (1) -(2) dormant horticulture oil treatments  applied in December/January and (2) insecticide treatments in June/August,

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