Not a disease.

Instead a slime mold. often referred to as dog vomit fungus.

Edit to add:
Ignore it. It's not a problem. It will disappear on its own

This post was edited by jean001a on Mon, Jul 1, 13 at 11:12

we need a pic..

but mulch is dead material.. it can NOT be diseased ...

and your problem is on the mulch.. which by definition.. means its not a plant problem.. or it would be on a the plant ...

decomposition of mulch is achieved by molds/fungus ...

its natures way .. its normal.. and it will end.. when they use up the rotting material in your mulch ...

think of it this way.. its a FREE SHOW of mother nature ...

it might also indicate that your mulch/compost was not fully 'finished' at the processors ...

relish the show.. and stop worrying ...

ken

Woody mulches tend to develop slime molds more then any other types and as indicated above they are not much of anything other than a visual problem.

Here is a link that might be useful: Slime Molds

I had pictured bird nest fungus when I read the description.