How to recognise it
Few plants will emerge from planted bulbs and, when dug up, the bulbs will have soil stuck to them and dry rot from the neck downards. There may be a whitish, mould-like growth on the bulbs and in the surrounding soil, with fungal bodies (“sclerotia“) which are round or flattened and up to 80mm in diameter, which later darken to nearly black.
Why it’s a problem
Any affected bulbs which do not sprout should be removed and destroyed as they are unlikely to recover.
Where you are likely to find it
Commonly found on tulips but can also occur on bulbous iris, ixias, cochicums, crocuses, hyacinths, lilies and narcissi. Occurs on bulbs which are in the ground (although it will persist if infected bulbs are stored).
How to prevent it
Destroy any bulbs which look as if they may be affected – re-planting them will just spread the disease to other bulbs. This process of removing diseased individuals to prevent the problem spreading is called ‘rogueing’.
Always handle bulbs with great care, any damage can provide an entry point for disease. Don’t store or re-plant any damaged bulbs. Applying a fungicide to bulbs prior to planting can help prevent an infection.
How to get rid of it
Remove all affected bulbs and the soil around them. The area is likely to remain contaminated by the fungus for at least 5 years (tests indicate that 10% of the fungi will actually live for over 10 years), so susceptible bulbs should not be planted in it during that period.
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Other useful information
On bulbous irises similar symptoms are caused by Sclerotium delphinii (although the fungal bodies tend to be more yellow-brown in this case). The treatment for this disease is the same and delphiniums should not be grown in the area for as long as possible.