Insect and Disease Problems

Insects and diseases can threaten a plants health. As soon as a change in a plants appearance becomes noticeable a careful examination should be done to determine the problem. By identifying the symptoms of the damage the problem can be diagnosed and an appropriate treatment can be determined.


  • Identify the plant. Many insects and diseases are plant-specific, this information can limit the number of diseases and disorders
  • Look for a pattern of abnormality. Compare the affected plant with other plants on site, especially the same species. Differences in color or growth may present clues to the source of the problem. Non-uniform damage patterns may indicate insects or diseases. Uniform damage over a large area usually indicates disorders caused by such factors as physical injury, poor drainage, or weather
  • Examine the landscape. The history of the property and adjacent land may reveal problems. The number of plant species affected may help distinguish between infectious pathogens that are plant specific as compared to chemical or environmental factors
  • Examine the roots. Note the color of the roots, brown or black roots may signal problems. Brown roots often indicate dry soil conditions or the presence of toxic chemicals. Black roots indicate overly wet soil conditions or the presence of root rotting organisms
  • Check the trunk and branches. Look for wounds as they provide entrances for pathogens and wood rotting organisms.
  • Position and appearance of affected leaves. Dead leaves near the top of a plant are usually the result of root stress.


Plants vary in susceptibility to pathogens. Even if the pathogen is present and a susceptible plant host is available, the environmental conditions must be present for the pathogen to infect the plant.

Three things are required for a disease to develop:

  • The presence of a pathogen (disease causing agent)
  • The plants susceptibility to the pathogen
  • An environment suitable for disease development

Examples of infectious agents include fungi, viruses, and bacteria. Non-infectious diseases can be caused by nutrient deficiencies, temperature extremes, pollutants, and fluctuations in moisture. Non-infectious disorders account for 70-90% of plant problems in urban areas. These disorders often produce symptoms similar to those caused by infectious disease, it is essential to distinguish between the two in order to give proper treatment.


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

Insects are divided into three categories according to their method of feeding: chewing, sucking, or boring. Insects from each group have patterns of damage that help determine the culprit and the proper treatment.

  • Chewing insects eat plant tissue such as leaves, flowers, buds, and twigs. Damage by these insects is often seen as uneven or broken margins of the leaves, skeletonization of the leaves, and leaf mining. Chewing insects can be beetles adults or larvae, or moth larvae (caterpillars) The damage can help to identify the insect
  • Sucking insects insert their beak into the tissues of leaves twigs, branches, flowers, or fruit and then feed on the plants juices. Examples of sucking insects are: aphids, mealy bugs, thrips, and leaf hoppers. Damage caused by these pests is often indicated by discoloration, drooping, wilting, leaf stippling, honeydew, or lack of vigor in the affected plant
  • Boring insects feed beneath the bark of a plant. Some borers kill twigs and branches. Eggs can be laid from the adult, and when they hatch feed inside the stems/branches of trees and shrubs. Beetles will lay eggs into the holes they bore to feed on plant tissue when hatched.

© 2016 LandcareLogic All Rights Reserved | 7370 Opportunity Rd., Suite G. | San Diego, CA 92111 | License # CSLB B, C27-915934 | Sitemap |

site designed by, Namtra Media, San Diego Web Design Company