In November 2011, amaranth (Amaranthus tricolor) cv. Garnet Red seedlings from a local nursery were submitted to the Florida Extension Plant Diagnostic Clinic in Homestead, Florida, USA. Symptoms began as a rot and that ultimately resulted in the loss of the entire planting of seedlings, causing post-emergent damping-off in both the greenhouse and shadehouse locations where the crop was grown. Based on morphological characteristics, sequence analysis of the rDNA internal transcribed spacer region and pathogenicity tests, the causal agent was identified as P. myriotylum. This fungus is an aggressive pathogen causing important economic losses with a very large host distribution worldwide in warm regions. In south Florida, it had previously been reported causing aerial blight of tomato, and more recently, basal rot on Echeveria. This is thought to be the first report of P. myriotylum causing damping-off of an Amaranthus species in Florida.