Wednesday, May 1, 2002

Insect and disease problems of trees

Insects and diseases can threaten tree health. With careful examination of the problem, identifying the specific symptoms of damage and understanding their causes, you may be able to diagnose the problem and select an appropriate treatment.

Basic elements that influence plant health include sufficient water, light, and a proper balance of nutrients. Too much or too little of any of these environmental conditions may cause plant stress.

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.

Diagnosis. Correct diagnosis of plant health problems requires a careful examination of the situation.

1. Accurately identify the plant. Many insects and diseases are plant-specific.

2. Look for a pattern of abnormality. Compare the affected plant with other plants on the site, especially those of the same species.

3. Carefully examine the landscape as well adjacent areas as this may reveal many problems. This may help distinguish between infectious pathogens that are more plant-specific as compared to chemical or environmental factors.

4. Examine the roots. Note their color: brown or black roots may signal problems.

5. Check the trunk and branches. Look for wounds because they provide entrances for pathogens and wood-rotting organisms. Wounds can be caused by weather, fire, lawnmowers, and rodents, as well as a variety of other environmental and mechanical factors.

6. Look at the appearance of affected leaves. Dead leaves at the top of the tree are usually the result of environmental or mechanical root stress. Twisted or curled leaves may indicate viral infection, insect feeding, or exposure to herbicides. The size and color of the foliage may tell a great deal about the plant's condition.

7. Sometimes a plants current problem is actually a result of something that happened to it much earlier.

Disease. Examples of infectious agents include fungi, viruses, and bacteria. Noninfectious diseases, which account for 70 to 90 percent of all plant problems in urban areas, can be caused by such factors as nutrient deficiencies, temperature extremes, vandalism, pollutants, and fluctuations in moisture.

Insects. Some insects can cause injury and damage to trees and shrubs. By defoliating trees or sucking their sap, insects can retard plant growth. 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.

Treatment. The treatment method used for a particular insect or disease problem will depend on the species involved, the extent of the problem, and a variety of other factors specific to the situation and local regulations. Always consult a professional if you have any doubt about the nature of the problem or proper treatment.

For more information or assistance call the Georgia Forestry Commission at 770-254-7218.

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