Aspergillus ear rot is caused by the fungus Aspergillus flavus and is recognized as an olive-green powdery mold that usually occurs at the ear tip or in association with damaged kernels. The fungus infects corn ears soon after pollination when the silks are yellow-brown but still moist. Infection and colonization of kernels are favored by hot (>86F), dry conditions during grain fill.
The fungus, A. flavus, may also produce a potent mycotoxin called aflatoxin. Hot, dry conditions with warm (>70F) nights and low kernel moisture (<35%) favor the production of aflatoxin. Not all strains of A. flavus produce aflatoxin. Grain contaminated with aflatoxin can cause feeding and reproductive disorders in swine, cattle and poultry, and has been associated with esophageal cancer in humans. For these reasons, the FDA has established an “action level” of 20 ppb for aflatoxins in corn for interstate commerce.