Black Mold

Black Mold on Harvested Tomato
Black Mold on Harvested Tomato (C. Trueman, University of Guelph)

Alternaria alternata
Alternaria alternata (Yong-ting Yu, Chinese Academy of Agricultural Sciences)

Casual Agent

Black mold is a late-season and post-harvest disease of tomatoes caused by the fungus Alternaria alternata.


Brown to black lesions appear on the epidermal tissue of ripe fruit. In warm, humid weather, the fungus sporulates to form a black, velvet-like layer on the surface of the existing lesions.

Disease Cycle

Black mold can appear in the field late in the season after a rain or dew. Fungal spores require 3 to 5 hours of moisture to germinate. 


  • Avoid overhead irrigation later in the season to keep tomato fruits dry.
  • Harvest tomato fruit as soon as they ripen.