( Sclerotium cepivorum )
This is a serious fungal disease caused by Sclerotium cepivorum, which affects all members of the Allium or Onion family. The leaves show yellowing and wilting due to the lack of roots. The bulbs remain in a stunted form with most roots and the basal plate rotted away. A white fluffy mould covers any of the outer skin which is underground.
It persists as small, dormant structures called sclerotia, which can remain in the soil for up to 15 years and are very easily transferred to other sites, even on the soles of shoes. Infested areas must not be used again for growing onions or garlic.
Infected plants should be removed and destroyed by burning or sealed in bags for dumping - never place on the compost heap. Any remaining bulbs should be well spaced to reduce the chance of them being affected. It can be brought in on onion sets and garlic cloves so some growers raise their crops from seed instead.
There is no chemical control for gardeners.
Commercial growers sterilize affected areas using methyl bromide fumigation, but eradication is not complete. Some work has been done using a petroleum based stimulant, diallyl disulphide, which has a similar sulphurous odour to alliums that causes the dormant sclerotia of the fungus to grow and since there are no roots present as a food source, it dies away. Other trials have used garlic powder which is cultivated into the ground and results are said to be similar to the petroleum-based compound.
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