noun Plant Pathology.
any of several diseases of plants caused by rusts and characterized by black discoloration resulting from the fungal teliospores.
Origin of black rust
An Americanism dating back to 1780–90
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a stage in any of several diseases of cereals and grasses caused by rust fungi in which black masses of spores appear on the stems or leaves
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012