Most problems with bulbous plants concern the part underneath the ground.
If the bulbs have disappeared entirely, mice are the cause. Swift moth caterpillars remove pieces from the bulbs. These are whitish caterpillars with brown heads. Even if the bulbs are not eaten entirely, the damaged ones will probably rot. Regular hoeing disturbs the swift moths’ life cycle. Attracting birds into the garden can help.
Bulb aphids are small insects which collect on stored bulbs and feed under the outer scales, damaging the young growth which appears after planting and causing localized rotting. Dust with derris at storage time.
Bulbs eaten, uneaten parts rotten
Narcissus fly. Bulbs are eaten in the ground by maggots about half an inch (15 mm) long, and go rotten. Watering the leaves and ground with an insecticide regularly after flowering will control this pest, as will hoeing around the foliage.
Eelworm affects daffodils, tulips, hyacinths, etc. Bulbs are soft and rotten with dark rings inside. Leaves (if any) are pale with small yellow swellings. There is no cure. Do not plant bulbs, corms, tubers, etc. on infested land for at least 3 years.
Do not plant soft bulbs. Be careful when accepting gifts.
Bulbs rotten in store or in the ground
Narcissus smoulder. A storage rot, characterized by small dark fungal growths on the outer scales.
Basal rot starts at the basal plate and spreads upwards through the bulb. Affects daffodil and narcissus bulbs in store.
Tulip fire. Black fungal growths appear on outer scales of stored tulips; leaves and flowers of affected bulbs are streaked, with brown ends.
Dry rot occurs on crocus and gladiolus corms in store and appears as black spots which eventually merge and all the tissue goes rotten.
Hard rot also occurs on stored corms. The spots are brown and the corm shrivels.
Scab is a corm rot which starts with brown, round, shiny scabby spots.
Core rot is a wet rot occurring in the central core of corms.
The control for rots is to dip stored bulbs in a fungicide before storage and dry off, and dip again before planting. With bulbs left in after flowering, watering with a fungicide may help a little. Dispose of all rotten bulbs and corms immediately.
Rotting is made much worse in cold, waterlogged soils so this type of environment must be improved if you intend growing bulbs there.
Tuber rot occurs in stored dahlia and begonia tubers. The usual cause is insufficient cleaning and drying off. A fungicidal dip at storage time will help, but make sure the tubers are dried off thoroughly afterwards. Small rotten parts can be trimmed off to healthy tissue. Regular inspection in store is essential.
Vine weevil grubs can eat tubers which then rot. Dust with HCH, or use one of the new organic nematodal controls now available.
Virus causes distortion, mottling and streaking of leaves and sometimes flowers. All affected bulbs should be dug up and burnt as soon as the disease is spotted, as there is no cure. Be careful of cheap bulbs and gifts. Thrips cause mottled streaking of gladioli leaves and flowers. Spray regularly with any insecticide (malathion, derris, etc.).
Birds will peck at crocus flowers and tear them to pieces for no apparent reason and there is little you can do about it. There are proprietary bird repellents you can water on, but they are not very effective and, in any case, they wash off when it rains. Plastic humming line can be a deterrent.