What common disease in ornamental plants causes damping off of young vegetable plants and is spread by mycelia fragments?

The correct answer is Rhizoctonia, which is known for causing damping off, a particular issue that affects young seedlings and can lead to significant losses in vegetable crops. This disease is characterized by the wilting and subsequent death of seedlings, often resulting from the pathogen's ability to invade and degrade the tissues close to the soil line.

Rhizoctonia is spread through mycelial fragments found in the soil or on infected plant debris. When conditions are favorable—such as high humidity, warm temperatures, and poor air circulation—these fragments can thrive and infect young plants. The disease primarily affects seedlings because their root systems are not yet established and are more vulnerable to soil-borne pathogens.

Successful management of damping off caused by Rhizoctonia typically involves practices such as ensuring good drainage in seedbeds, utilizing sterile potting soil, rotating crops, and maintaining proper plant spacing to enhance airflow around seedlings. Understanding the role of Rhizoctonia in plant health is essential for anyone involved in horticulture, especially in regions where it might be prevalent.