Ear and Kernel Diseases
Part 2, Section 2: Corn Pest Management
Corn Pest Management
Ear and Kernel Diseases
Ear and kernel diseases are important to diagnose mostly due to the possibility of mycotoxin production (see Moldy Corn and Toxin Production below). In addition to toxin production, ear and kernel diseases cause reduced test weight and lower grain quality. Many of these diseases are often associated with insect or other damage to the ear. The best method for halting fungal growth is proper drying of the grain to 15 percent moisture or less, but neither drying nor heat will reduce mycotoxin levels if present.
Research has shown that the presence of the Bt (Bacillus thuringiensis) gene in corn has reduced the likelihood of ear and kernel diseases when compared to conventional hybrids. The production of Bt throughout the corn plant reduces insect damage to the ear, therefore minimizing that method of entry for the fungal pathogens. This is especially important when fungal pathogens producing mycotoxins have been an issue in the past.
Aspergillus ear rot can become an issue during periods of drought, extreme heat, and corn ear injury from insect feeding. Although this is usually not an economic disease due to the fact it only colonizes a few kernels and not an entire ear, the pathogens involved can produce aflatoxins, which are extremely toxic compounds. The signs of the disease vary depending on the age of the infection, usually yellow-green fungal masses that turn to dark green or brown. If a high portion of ears are affected, the grain should be analyzed for mycotoxin concentrations.
Diplodia ear rot infects the plant just after flowering. Typical signs of Diplodia on the ear are a white or grayish mass of mycelium with black structures specks, pycnidia (survival structures), produced on the husks, kernels, cobs, and even the stalks. Diplodia does not produce mycotoxins, but it will significantly reduce grain quality. This disease overwinters within infected debris and can be troublesome in continuous no-till planted corn. Crop rotation and fall tillage has been known to reduce the inoculums levels.
Fusarium kernel or ear rot is most severe when hot, dry weather occurs at or just after flowering. The sign of this disease is often a whitish-pink fungal growth on kernels. This disease can also be seen on the tip of the ear associated with insect damage from earworms or other pests. In severe cases, the entire ear may exhibit signs of the disease. The major concern of this disease is the likelihood of mycotoxins produced in the corn grain. The Fusarium family of pathogens is very good at overwintering on debris; therefore, crop rotation and tillage will reduce inoculum levels in severely infested fields.
Gibberella ear rot is characterized as a reddish mold that starts at the tip and grows down the ear. In severe cases the entire ear may be affected. This disease is also associated with Gibberella stalk rot of corn as well as Fusarium head blight (scab) of wheat. The stalk rot is also characterized by reddish-pink discoloration inside the stalk. Again, the major concern is the potential of mycotoxin production. This disease can affect silage, and corn not properly ensiled can lead to mycotoxin issues in the feed. The association of Gibberella with both corn and wheat has led to high levels of Fusarium head blight in wheat following corn silage with that had high levels of stalk rot. In severely infected corn fields, crop rotation and tillage will help to reduce inoculums levels.
Penicillium ear rot is commonly found on ears with insect, bird, or other damage. The sign of this disease is powdery green or blue mold between kernels, usually near the tip of the ear. This disease is not often considered economically important in corn for grain, but it can pose problems in both high-moisture corn and corn silage.