Sclerotium cepivorum is a pathogen that causes a devastating disease in onion plants and other related species. This fungus is known for its ability to survive for long periods in the soil in the form of sclerotia, which are resistance structures. When conditions are favorable, these sclerotia germinate and produce fungal structures called mycelium, which infect the roots of the host plants.

The disease it causes in onions is known as "white neck rot" or "white root rot." Symptoms include decay of the neck and base of the plant, leading to sudden collapse and death of the plant. A characteristic white mold is often seen on infected areas. This disease can cause significant losses in onion crops and is especially problematic in regions with hot, humid climates.