07/18/2022
Tree Insect and Disease Problems
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. This helps limit the list of suspected diseases. Treatment without confirmation of the issue is often ineffective.
2. Look for a pattern of abnormality. Compare the affected plant with others on the site, especially those of the same species. Non-uniform damage patterns may indicate insects or diseases. Uniform damage over a large area usually indicates disorders caused by physical injury, poor drainage, chemical damage, or weather.
3. Carefully examine the landscape. The history of the neighboring property may reveal problems. Most living pathogens take a long time to spread, so if a large percentage of plants are affected quickly, a pathogen or insect is probably not involved.
4. Examine the roots. Brown roots may indicate dry soil or the presence of toxic chemicals. Black roots may indicate overly wet soil or the presence of root-rotting organisms.
5. Check the trunk and branches. Wounds caused by weather, fire, mechanical damage, or animals can provide entrances for pathogens and wood-rotting organisms. Large defects may indicate a potentially hazardous tree.
6. Note the position and appearance of affected leaves. Leaf damage alone is not generally sufficient to identify the pest or disease. Evidence of the affliction is needed to confirm the issue.
Insects
• Some insects cause injury and damage to trees and shrubs. Generally, the insect problem is secondary to problems brought on by a stress disorder or pathogen.
• Most insects are beneficial rather than destructive. They help with pollination or act as predators of more harmful species.
• Killing all insects without regard for 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, and boring. Insects from each group have characteristic patterns of damage that help with diagnosis.
•Chewing insects eat plant tissue such as leaves, flowers, buds, roots, and twigs. Damage by these insects is often defined by uneven or broken margins on the leaves, skeletonization of the leaves, and leaf mining. Chewing insects include beetle adults or larvae, moth larvae (caterpillars), and many other groups of insects. The damage they cause (leaf notching, leaf skeletonizing, etc.) will help in identifying the pest insect.
•Sucking insects insert their beak (proboscis) into the tissues of leaves, twigs, branches, flowers, or fruit and then feed on the plant’s juices. 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 plant.
•Boring insects spend time feeding beneath the bark of a tree as larvae. Some borers also kill twigs and leaves, either when adults feed or when larvae bore into stems after hatching from eggs. Other borers, such as bark beetles, mate at or near the bark surface and lay eggs in tunnels beneath the bark.
Diseases
Three things are required for a disease to develop:
A pathogen (disease-causing agent).
2. A plant susceptibility to that particular pathogen.
3. 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. Diseases can be classified into two broad categories: • Infectious: transmittable diseases caused by microscopic living agents. • Non-infectious: non-transmittable diseases that are inherited or the result of non-living agents. Examples of infectious agents include fungi, fungal like microorganisms, viruses, and bacteria. Non-infectious diseases, the majority of plant problems in urban areas, can be caused by such factors as compacted soil, nutrient deficiencies, temperature extremes, vandalism, pollutants, and fluctuations in moisture. Non-infectious diseases often produce symptoms similar to those caused by infectious diseases. It is essential to distinguish between the two to determine proper treatment options.
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.