Rotten parsley

My bed of parsley is doing really well except now and then a plant dies over a period of a week or two. The roots turn to mush and then the leaves wither and turn yellow. I reckon it's a fungus attacking the roots.
The question is: what sort of fungus is it and how do I deal with it?
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Where do you live? Are these plants that've been in the ground since last summer, or new ones you installed this season? Describe the growing conditions (shade, sun, etc) and what your weather's been like.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.