A LOT of readers will flinch when I mention the words “white rot,” a disease which often becomes apparent at this time of the year as garlic, shallots or overwintered onions are lifted.

I apologise — I know it’s a sore subject, but there may be good news, so please read on.

The reason white rot is so dismaying to gardeners is not only that it can render an entire crop unusable, but also that once your soil is infected it can remain so for many years.

Just to put a cherry on top, it’s very easily spread from plot to plot on boots and tools.

White rot affects members of the allium family: onions, leeks, garlic and so on. The first sign you’ve got it is often the leaves of the plant dying away, as if ready to harvest, but prematurely.

The symptoms on the below-ground part of the vegetable are not easily mistaken for anything else: the bulb, starting at the base where the roots are, will be partly or entirely rotten with white, fluffy matter visible. (I won’t insert any jokes about Starmerism here, in case it’s too soon.)

Traditionally, the only solution to white rot is not to grow alliums in that piece of ground for the foreseeable future, though growing in pots and other containers in bought-in potting compost, instead of soil, can work.

There are no chemical controls. For a home-grower white rot is disappointing; if you grow onions for a living, it can be devastating.
But over the last few years a glint of hope has arrived.

Stromatinia cepivora has a weakness built-in to its lifecycle. Although the disease can lie dormant in soil for years, waiting to detect the chemical signature of allium which will bring it back to life, it can only do so once.

This gave some clever people the idea of fooling white rot into germinating, finding no host plant present on which to grow, and therefore dying, leaving the soil clean.

Various methods of achieving this have been experimented with, but the one which is suitable for trying at home, because it’s simple and not too expensive, is to use garlic powder.

In powder or granule form, garlic is readily available online from (for some reason) equine veterinary suppliers.

At a time when your infected soil is unoccupied and warm (late spring to early autumn) you sprinkle the garlic generously over the ground, and rake it in.

Unfortunately, I had cause to test this trick a couple of years ago. I’m avoiding saying it worked, because that suggests cause and effect of which I have no solid evidence. What I can say is that the next onion crop in that patch suffered no losses to white rot.

I earnestly hope that you never need to try the experiment, but if you do ever suffer from white rot, the garlic treatment is definitely worth a go. Many growers swear by it, albeit in the absence of any scientific consensus.