White Rot
Sclerotium cepivorum
A devastating soilborne fungal disease of onions, garlic, and other alliums that rots the roots and base of the bulb. White rot is feared because its tiny resting structures survive in the soil for decades, so once a garden bed is infested it is extremely hard to grow alliums there again.
🔎 How to spot it
Above ground the leaves yellow, wilt, and die back starting with the older outer leaves, and infected plants pull up easily because the roots have rotted. At the base of the bulb you find a fluffy white mat of fungal growth that later becomes packed with numerous tiny, round, black resting bodies about the size of poppy seeds. The bulb itself develops a soft, semi-watery rot.
🥀 Damage it causes
The fungus destroys the roots and rots the base and scales of the bulb, killing the plant outright or leaving a rotten, unusable bulb. Losses can be total in an infested bed, and the rot often continues in storage. Because the black sclerotia persist in the soil, the damage carries over from year to year.
🔬 What causes it
White rot is caused by the soil fungus Sclerotium cepivorum, also called Stromatinia cepivora, which attacks only onions, garlic, leeks, and their relatives. It is favored by cool, moist soil, with disease worst around sixty to sixty-five degrees, and just a few sclerotia per unit of soil can infect a planting. The sclerotia can survive in the soil for twenty years or more, waiting for an allium root.
🛡️ Prevent it
The single most important step is to keep the fungus out: never bring in infested soil, transplants, sets, or garlic cloves from an unknown source, and clean soil off tools and boots. If a bed becomes infested, do not grow alliums there, since rotation cannot outlast the sclerotia. Plant only clean stock in cool but not cold soil, and avoid moving soil from a contaminated area.
🧯 If it is already here
There is no cure once white rot is established; affected plants should be pulled and destroyed, not composted, along with the surrounding soil if practical, to slow the spread of sclerotia. Home gardeners essentially cannot eradicate it, so the realistic response is to stop growing alliums in the infested ground and start fresh, clean beds elsewhere. Keeping the pathogen from ever arriving is the only reliable control.
💡 Good to know
White rot is one of the most serious diseases an allium grower can face precisely because the soil stays infested for decades, far longer than any practical crop rotation. The black, poppy-seed-sized sclerotia in the white mat at the bulb base are the diagnostic sign. Buying certified clean garlic and onion stock is the best insurance against introducing it.
🌱 Plants it affects
22 plants in the library can be affected by this problem
Cipollini Onion
Common Chives
Egyptian Walking Onion
Elephant Garlic
Garlic Chives🧄German Extra Hardy Garlic
Globemaster Allium🧄Inchelium Red Garlic🧄Killarney Red Garlic
Leek
Music Hardneck Garlic
Pearl Onion🧅Red Onion
Scallion
Shallot
Softneck Garlic🧅Spanish Onion🧄Spanish Roja Garlic
Vidalia Sweet Onion🧅Walla Walla Sweet Onion
White Onion
Yellow Sweet OnionFor educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.