What symptom is often caused by honeydew-producing pests like aphids and scales, visible as a black sooty mold?

• A. Powdery mildew on leaves.
• B. Yellowing of leaves with necrotic spots.
• C. Sooty mold on leaves.
• D. Stunted growth with brittle stems.

Answer: (C)

Sap-sucking pests like aphids and scales excrete honeydew, a sweet substance that coats leaf surfaces. A fungus then grows on that honeydew, producing a black, shiny film known as sooty mold. This mold is the visible symptom described, appearing as a dark coating on leaves. It can shade the leaf surface and reduce photosynthesis, weakening the plant, though the mold itself doesn’t invade the leaf tissue. Because sooty mold relies on ongoing honeydew, removing the pests or washing the leaves can make the mold disappear once the source of honeydew is gone. The other options describe different problems: a white powdery coating is due to powdery mildew, not honeydew; yellowing with necrotic spots points to nutrient issues or other diseases; and stunted growth with brittle stems indicates environmental stress or structural problems, not honeydew-associated mold.