Damping Off' diseases are the bane of seedlings. It is the gray white furry fungus that forms on the stems of your seedling right where they meet the starting mix. Sprinkl cinnamon on the infected seedlings as a way to kill off the fungi or 'damping off' disease and stop its potential spread.
You could also lightly sprinkle your starting mix with cinnamon right after the seeds are planted. You can, in addition, also use the cinnamon at first signs of the disease and sprinkle the infected cell and surrounding cells. That is your choice.
I think cinnamon makes a great third defense against diseases that may attack your seedlings.
Source : Using Cinnamon on Seedlings: Stop 'Damping Off' Diseases!