How to recognise it
On most affected plants this fungus appears as one or several large, irregular red/brown patches on the sides of stored bulbs, corms or tubers (these areas are tan or grey when onion or garlic bulbs are infected). There may be small, pinkish coloured fungal bodies beneath the skin at the centre of the infected area. If it’s moist, white or blue/green mould may grow on the patches, from which a grey/brown dry rot may spread into other parts.
When irises are affected a soft rot spreads from around the bulb or from the base of the bulb, and a blue/green mould may appear.
Why it’s a problem
The rot develops rapidly in storage, particularly in cool, humid conditions and can pass from the soil to uninfected bulbs/corms/tubers. Affected plants will rot and should be destroyed.
Where you are likely to find it
Affects many different types of ornamental bulbs, corms and tubers. This includes, crocuses, cyclamens, freesias, gladioli, hyacinths, irises, lilies, narcissi (daffodils), scillas, tigridias and tulips.
Onion and garlic bulbs can also be affected.
How to prevent it
Bulbs/corms/tubers which are damaged are more susceptible to infection through the wound, so careful handling is important, particularly when lifting and storing them. The lifted bulbs should not be exposed to direct sunlight as this can also damage them. No damaged bulbs/corms/tubers should be stored.
When harvesting onions or garlic, ensure that they are thoroughly dry (by leaving on the soil surface in warm, dry weather for a few days) before storing them.
Keep the storage conditions dark, cool, dry and well ventilated, to prevent the humid conditions in which this disease can spread.
How to get rid of it
Dig up any affected plants and destroy them. Also remove and discard a spadeful of the surrounding soil to remove any fungi within it.
If any area has been contaminated by the fungus then you should wait around 3 years before replanting with bulbs, corms or tubers.
Is it good for anything?!
Other useful information
Penicillium expansum is another species of blue mould rot. It affects fallen or stored apples, pears, oranges, quinces and other fruit.