True to its name, this fungal disease causes onion necks to shrivel and turn brown and soft inside. Although infection occurs while plants are in the field, the disease may not become apparent until bulbs are in storage, when a gray, powdery mold appears in the dry outer skin. Neck rot usually leads to other diseases, such as soft rot, which will destroy bulbs in storage.

White onions are usually more susceptible to neck rot than yellow or red onions. Wet weather and poorly-drained soil favors development of this disease.

• Grow onion family crops in well-drained soil. Promote good air circulation by giving plants plenty of growing space.
• Provide only as much nitrogen fertilizer as plants need to maintain healthy growth.
• Remove all onion plant debris from the garden after harvest.
• Let onions dry thoroughly before storage so the necks are tightly closed and contain no moisture. The fungus can't spread into the bulb if the neck is completely dry.
• Store onions in proper conditions (34 degrees F and 75 percent relative humidity).
• Check stored bulbs monthly and destroy any that show signs of disease.