Aspergillus ear rot of corn
Aspergillus ear rot is one of the most important diseases of corn. It is caused primarily by the fungus Aspergillus flavus, but a few other Aspergillus species may be involved. Typically, this disease is more common in the southern United States than in other areas. Aspergillus ear rot appears as an olive-green mold on the kernels that may begin at the tip of the ear or be associated with injury from insects, birds, or hail. The fungal spores appear powdery and may disperse like dust when you pull back the husk. These signs are most commonly observed at the tip of the ear, but can be scattered throughout the ear and all the way to the base of the ear.
Aspergillus species produce a mycotoxin called aflatoxin. Aflatoxin affects grain quality and marketability and is primarily a threat to livestock health. Aflatoxin is extremely carcinogenic and most countries (including the United States and Canada) have regulations in place to prevent aflatoxin from entering the human food and livestock feed supply. The aflatoxin, which will accumulate as the fungus spreads in subsequent hot and dry weather. The fungus can infect the ear and produce more aflatoxin after physiological maturity, particularly during periods when rainfall delays harvest. It’s important to note that kernels with no visible injury or mold may still contain aflatoxin.
The Aspergillus fungus survives in soil or crop residue and infects ears during late silking. Spores are spread by wind and insects and infection takes place through insect wounds or other types of wounds or through the silks. Hot, dry conditions favor infection. Stressed plants (from nutrient deficiencies, drought, or feeding damage from ear-invading insects) are often more susceptible to this disease.
Scouting prior to physiological maturity is important to identify areas with mold problems. These areas should be harvested as soon as possible to prevent further mold development. Harvested grain should be cooled, dried, and cleaned immediately after harvest, and stored apart from grain harvested from healthy fields. Insect management reduces the risk of ear rot infection.
Gallery images: G. Munkvold, T. Faske, and A. Robertson.