Watch for ear molds in 2011

Corn ear molds have been observed at the University of Illinois Northwestern Research and Education Center in Monmouth. In plant pathology, we like to talk about the disease triangle. Not only must a susceptible hybrid and the pathogen be present, but weather conditions must be conducive for disease development. While moderate temperatures and moist weather favor Gibberella and Diplodia ear molds, hot, dry weather as we've experienced in 2011 favors Aspergillus and Fusarium ear molds.

Although ear mold fungi can reduce yield by consuming grain dry matter, of far greater importance is that many of the fungi produce chemicals called mycotoxins, byproducts that are toxic to humans and other animals.

To scout for ear molds, choose several locations in the field and peel back the husk leaves from the ears of several plants. If you observe mold, proper diagnosis can help you determine your risk of mycotoxin contamination, as not all ear mold fungi produce mycotoxins. The University of Illinois Plant Clinic can diagnose ear molds.

Aspergillus ear mold. Aspergillus ear mold is caused by two fungal species, Aspergillus flavus and Aspergillus parasiticus. The fungus survives and sporulates on infected crop residue. Fungal spores are disseminated through the air and can infect kernels either by growing down the silk channel or by entering insect-feeding wounds. Aspergillus ear mold is favored by drought, high temperatures, and high relative humidity during pollination and grain fill.

A corn ear infected by Aspergillus ear mold. Signs of Aspergillus should be easy to see; they most often develop near the ear tip (due to insect feeding) or at any spot where the ear has been damaged. Aspergillus produces a powdery grey-green growth on and around kernels.

The presence of Aspergillus ear mold indicates the potential for mycotoxin contamination in your crop. Some strains of A. flavus and A. parasiticus produce aflatoxin, a mycotoxin that is toxic to liver tissue and carcinogenic.

An inexpensive way of determining whether you have risk of aflatoxin contamination is to illuminate infected grain with a blacklight (365 nm). However, this method is neither quantitative nor accurate, as some strains of A. flavus fluoresce but do not produce mycotoxins. Chemical analysis is required to determine whether your corn contains aflatoxin.

Disease control includes residue management, such as chopping or burying residue to aid decomposition. Also, anything you can do to minimize stress in your corn plants, such as planting drought-tolerant hybrids, irrigating, ensuring adequate soil fertility, and controlling insects through Bt traits, can reduce your risk of Aspergillus ear mold.