What are the signs and symptoms of corn smut infection?

The presence of tumor-like galls and black powdery spores is the hallmark sign of corn smut infection, which is caused by the fungus Ustilago maydis. These galls typically form on various parts of the corn plant, including ears, stalks, and leaves. As the galls mature, they produce a dark, powdery mass of spores, which can be dispersed by wind or rain, facilitating the spread of the disease. This distinctive sign is crucial for identifying corn smut and differentiating it from other plant diseases.

The other options may represent symptoms of various plant health issues but do not accurately describe the specific indicators of corn smut. Yellowing leaves, while a common symptom associated with many plant problems, does not specifically indicate corn smut infection. Similarly, wilting of plants may be linked to various stressors, including drought or root issues, and leaf drop can occur due to many factors, such as environmental stress or pathogen attack, but they are not characteristic of corn smut. The unique signs of galls and spores are critical for diagnosing and managing this specific pathogen effectively.