Damping off

From PLANTFACTS.OSU.EDU

1. A disease of seeds or young seedlings caused by fungi.

This photo demonstrates what the roots of a plant look like when infected by damping off.
Source: http://www.pfc.forestry.ca/diseases/nursery/pests/damping_e.html



This is what a field looks like resulting from damping off.
Source: http://www.forestpests.org/nursery/dampingoff.html