rotting vegetable roots

by Susan
(Switzerland)

I found that about 2/3 of my parsnips and onions, both from dug and undug beds, had rotted from the bottom of the root up. I harvested the whole lot in August before I lost the whole crop. The parsnip were magnificent in June and started wilting near the end of June, I pulled the wilting ones up and the whole root had rotted away.

Later in August I noticed two chicory (for forcing) wilting in the parsnip bed, same story. Two plants left in the row who seem to be doing fine.

Is this a disease in the ground? Does it spread by mulching with the tops? How to avoid it?

This is an allotment site which I have had for 3 years. This is the first time this has happened. Before I had the plot it was an allotment for more than 20 years.

The soil in the plots around mine is 20cm higher as they have added compost over the years and evidently my predecessor did not. Soil underneath is clay. I started with manure, straw and compost in raised beds four years ago in November, then added straw/compost for mulch. The bed in question did not have straw on this year. It was dug and had peat added by a friend who I lent it to for the first two years. He had mixed crops in it which seemed to do fine, though he hardly harvested. I added a layer of municipal compost for this season.

There is occasionally standing water in another part of the allotment but my raised beds are above the "waterline". I do not think problem was damp, like I said they looked great and then suddenly wilted. This was beginning of August (I just checked the dates)

I am in Switzerland, Lake Geneva region, and the carrots for sale here have to be kept in the fridge or they will get slimy black splotches and rot, is this related?

Anyway I really want to know if sheet composting (I just cover all the debris with compost and sow into that) poses a risk of the disease returning.