What to expect with corn ear rots in 2019
Oct. 9, 2019
Planting had a very late start in most areas of the Corn Belt this year due to excessive rains in the spring. Hot and dry weather during the summer was not conducive to most leaf disease organisms, though gray leaf spot was established in some areas. Depending on the micro-climate in various areas, there may be the prevalence of certain ear and kernel rots this year. The amount of rain received during grain-fill period is related to the amount of kernel and ear rots. The most important ear rots are:
Diplodia ear rot is caused by a fungus, Diplodia maydis, which also causes stalk rot. Infections occur within two weeks after silking. The shank and the husks of the infected ears look bleached or straw colored. Infections usually start at the base of the ears and later spread to the kernels and eventually the whole ear may become rotted. When the husks are peeled back, a white mold is visible between the kernel rows.
Fusarium ear rot is caused by the fungus Fusarium moniliforme and is a widely spread disease that attacks corn ears and kernels. It produces pink to red discoloration of the kernels and usually starts at the tip of the ears. Infected kernels become covered with the pink mold which contains millions of microscopic spores. This fungus may also cause stalk rot.
Gibberella ear rot is caused by the fungus Gibberella zeae. It starts at the tip of the ear and also causes stalk rot. The kernels become reddish as the disease spreads to the entire ear. This ear rot is toxic to pigs, dogs and other similar stomachs, causing vomiting, weight loss and even death. Pigs refuse to eat infected corn on the ear if more than five to 10 percent of the ears are rotten.
Aspergillus ear rot is caused by the fungus Aspergillus flavus. It can become important in hot and dry seasons; corn with nitrogen deficiency may be more susceptible to it. This pathogen infects the ears damaged by corn ear worms, corn borers and other insects. It is usually found on ear tips. High temperatures favor the development and spread of this disease. It produces a bluish-green to green mold on the kernels. The fungus produces carcinogenic aflatoxin which can cause serious feeding problems in animals and human food. In stored grain, it can cause serious losses because the grain infected with this fungus may be rejected by the elevators based strict limits by the FDA and USDA.
Corn smut is caused by the fungus Ustilago zeae. It produces big galls of plant tissue which are full of black spores. As seen earlier in the Corn Watch ’19 field, it can attack any part of the plant throughout the growing season. The spores usually enter plants through injuries caused by insects or mechanical damage. If it occurs on the lower parts of the plants, it can cause barrenness. Dry weather or abnormally cool and wet weather is conducive to smut infection.
There are several other ear rots, such as Cladosporium, Trichoderma, Pennicillium and Nigrospora ear rots which are usually not of economic importance. Most of the above fungi over-winter in stored grain, soil surface or crop residue. Continuous corn tends to increase the incidence of these diseases. Crop rotations and cover crops keep the soils healthy and reduce the level of these pathogens.