Which of the following is a sign of pesticide misapplication on ornamental plants?

Leaf burn or discoloration is a clear indicator of pesticide misapplication on ornamental plants. When pesticides are applied improperly—such as using the wrong concentration, applying during inappropriate weather conditions, or using a product that is not suited for the specific plant type—it can lead to physiological stress in the plant. This stress often manifests as leaf burn or discoloration, which can range from yellowing or browning of the leaves to scorch marks.

In contrast, while excessive leaf growth may indicate strong health or perhaps some unintended fertilization effects, it is not directly a sign of pesticide misuse. Rapid flowering can suggest that a plant is thriving or responding to optimal growing conditions, which doesn't inherently relate to pesticide application errors. Lastly, increased pest activity could result from missed pest treatments but isn't a direct symptom of misapplying pesticides. In fact, misapplication often leads to pest activity rather than an increase in it immediately. Therefore, leaf burn or discoloration serves as a more explicit sign of potential issues arising from pesticide misapplication.