Onion white rot

What you see

Leaves yellow and wilt from the tip while the plant is still young. Lift it and the roots have rotted away, replaced by a dense white fluffy mat at the base of the bulb studded with tiny black poppy-seed dots.

Conditions

Cool, moist soil, 15-20C - so it does its damage in spring and autumn, not high summer. The black resting bodies survive in soil for fifteen to twenty years and germinate only when they sense an onion root nearby.

Treatment

No treatment exists. Lift and bin every affected plant with as much surrounding soil as you can, and do it carefully - the aim is to remove resting bodies rather than scatter them.

Prevention

Never move soil, tools or boots from an infected bed to a clean one. Grow alliums in containers or new ground. Some growers drench clean ground with garlic extract out of season to make the resting bodies germinate with nothing to feed on.

Months: March, April, May, October, November

Plants

Onion, Garlic, Leek, Shallot, Spring onion, Chives

Remedies

Not recorded — the field is blank rather than guessed.

The thing people get wrong

This is the one soil disease that genuinely ends allium growing in a bed, and gardeners regularly spread it themselves in a single afternoon - on a fork, on boots, or in a barrow of soil moved to another bed. Twenty years of viable resting bodies is not an exaggeration. If you find it, quarantine that bed for alliums permanently and grow your garlic in pots of fresh compost.