Although you may not have ever heard of Aspergillus niger, you may have already encountered it. Aspergillus niger is the scientific name for a fungus that causes the disease black mold in certain plants, including fruits and vegetables. Some archeologists believe that black mold-infected grain may be the primary cause of the final plague upon Egypt in the time of Moses, and may be behind the deaths of archeologists who excavated King Tutankhamen’s tomb. Because black mold can make you sick if you breathe or consume it, identifying Aspergillus niger is important.
Examine plants for signs of black or brown discoloration along damaged tissue. For example, black mold may appear on onions around the neck, where the plant protrudes and may become bruised from wind action. Other areas on an onion that may become affected include the roots or split surfaces in the onion layers. In grapes, Aspergillus niger may cause summer bunch rot, in which a single grape in a cluster appears brown and leathery. As the grape shrivels, the remaining grapes in the cluster will take on the discolored appearance.
Look over plants for black spores. Black spores collect along plant veins or the outer skin of a fruit or vegetable.
Leave the plant untouched. Plants initially infected with Aspergillus niger may appear water-soaked at first. Over time, the plants will dry and shrivel. On grapes, the individual fruits will take on a prune-like appearance.
Observe the conditions that the plant’s decline appears under. Aspergillus niger frequently develops in damp conditions when temperatures are higher than 86 degrees F. The spores may develop in plant storage, as with onions, or while the fruit or vegetables are still on the vine, as in the case with grapes.
Collect damaged material and place it in a sterile plastic bag. Send the material to a laboratory that specializes in diagnosing fungal diseases. According to the University of Maryland, two good laboratories for mold testing are The Mold Source and The Mold Testing Lab.