Onion white rot

Onion white rot is a serious fungal disease that can persist in the soil for 20 years or more.  It is caused by fungal spores which are black dots that lie dormant in the ground till triggered by onions growing nearby.
This year, out of a bed of about 100, I found 9 infected.

This picture shows 2 onions, one with much more infection.

   

And this shows the worst one cleaned up. It obviously needed using fairly quickly.

   

I have a garden area where white rot exists that I am slowly trying to eradicate. It is taking a long time. I've probably been at it now for 10 years but it was a lot worse then. I only grow autumn planted seeds/sets there and cycle round the plot in a 5 year cycle. Autumn planted sets can be harvested a lot earlier than maincrop and the fungus doesn't seem to develop till the soil warms up and these are then nearly ready to harvest. Autumn planted will store for a lot longer than books say but obviously not as long as maincrop. In last year's plot, there were no onions infected but this year I found a few. Any with yellowing leaves I give a pull to check the roots are still there as the fungus tends to travel up the roots to the bulb. When I found the one above, I pulled up the rest of the crop ,a bit early but of a reasonable size to use. I'm hoping by doing this, I'm removing the onions before more spores can form so reducing the prevalence in the soil. I also take out and dispose of a small spadeful of soil round any onions found.