This season I have had several questions on controlling ear rots in corn. Ear rots are caused by several different fungal species. The most common in our area are Diplodia, Gibberella, and Fusarium ear rots. Others, such as Aspergillus, and Penicillium ear rots are less common in our area, but do occur on occasion. Ear rots can enter ears either directly, such as in Diplodia, through the silks, as is seen in Fusarium, or secondarily as a result of insect or abiotic damage to the ear or husk.
Managing ear rots in corn: Focus on reducing the source of inoculum and minimizing stress. Fungal pathogens that cause ear rots are mostly derived from corn residue, and some hybrids are more prone to issues than others. Rotation to soybean or small grain/double crop soybean will help reduce the amount of corn residue available the next time corn is planted in a field. Tillage that buries residue also will help reduce the amount of available inoculum in a given growing season.
Damage to the ear increases ear rots by providing entry points for the fungi to enter the ear. Minimize ear rots by following good insect management practices and using Bt corn when possible. Some hybrids may be more prone to ear rots because of physical characteristics associated with the cob, such as poor husk cover, which also can provide entry for ear rot fungi. Lastly, stress, such as water stress at pollination or shortly after pollination can result in deformed or open husked ears that are more easily infected by ear rot fungi.
What about fungicides for ear rots?
Yes there are fungicides that have ear rot suppression on their labels. However, you can imagine that adequate coverage of the silks and husk is going to be an issue. Remember that the fungicides we use are going to be taken up locally and most will move up plant tissues with water gradients. Therefore, the fungicide is not likely to have any direct effect on the kernels themselves, but rather the silks and husk. Insect damage, open husks, etc. after VT allow entry points that will not be suppressed by fungicides, even if thorough coverage was attained. A recent publication in Plant Health Progress examined fungicide efficacy and timings for suppressing Diplodia ear rot in corn. The researchers conducted field studies at two locations from 2011 through 2013 to test two fungicides (Proline and Quilt Xcel) against Diplodia ear rot. Fungicides were applied at V6, VT-R1, and R3. Researchers found that fungicides did not consistently reduce Diplodia ear rot compared to untreated controls in any year.