Try to eliminate other causal factors first. The symptom may indicate a problem in a different part of the plant. For example, leaf yellowing and scorching may be caused by root damage. There is a great variation in the expected life-span of landscape plants. All plants go through periods of growth, maturity and decline.
Plants grown in urban conditions generally have shorter lives.
Many pests and diseases are plant-specific. Symptoms affecting more than one plant species may indicate cultural and environmental problems. Look for a pattern to the injury. Identify the pest, disease or problem. This is critical to making a control decision.