If you dug up the daffodils to divide or replant and find that the daffodils have rotten at the bottom even though it was not a particularly wet season, then probably they are suffering from basal rot, a fungus disease so called because it spreads from the bases of many bulbs and corms, including those of crocuses, lilies and daffodils. The disease can attack at anytime of the year.
A gardener will usually not realise his plants have basal rot until he lifts the bulbs for storage, though he will get some warning in the case of crocuses, whose growing foliage turns yellow and dies.
To confirm the diagnosis, cut a suspect bulb in half lengthways. If it has basal rot, dark strands will be visible spreading upwards from the base of the bulb, or the inner scales will be marked with chocolate-brown stains.
In the early stages of the disease, many bulbs can be saved by cutting out the affected parts and then soaking what’s left for about half an hour in a spray-strength benomyl solution.
Badly affected bulbs, however, are not worth bothering with. If basal rot has been a problem before, the best way to protect bulbs and corms against it is to soak them for 1 5-30 minutes in a spray-strength solution of benomyl or thiophanate-methyl. Both chemicals are systemic fungicides, and both work in much the same way. A routine immersion before planting, and another before putting them into store, should keep the rot at bay.