Fungi invading grain while on the ear vary by season, location and hybrid. In many cases the actual invasion of the grain occurred through the silk during pollination time of the season. The channel in the silk in which the germinating pollen tube grows towards the ovule is often the same channel for invasion by a fungus. This channel closes after the pollen tube passes, essentially closing the path for the fungal mycelium. Avoidance of fungal invasion into the ovule and therefore the developing grain is highly dependent on pollination occurring soon after silk emergence from the husks around the young ear.
Circumstances that tend to delay pollination include drought pressure at flowering time, causing delay in silk emergence but not in release of pollen. Less pollen available results in scattered kernels on ears or no grain at ear tips because pollen was expired before the silks leading to these ovules were gone. Aspergillus and Ustilago (smut) species produce spores during dryer environments.
Extensive rain during pollination time can also result in more infected grain. Pollen is not released from anthers when wet from rain. Silk emergence is enhanced with high water tension. These dynamics tend to delay pollination of exposed silks, as well as encouraging sporulation of Fusarium, Gibberella and Diplodia species.
After entering the ovule, these fungi can successfully invade the developing embryo and endosperm. In many cases this becomes evident as a molded kernels and in some cases the infections are not evident but only show later if the grain is not dried relatively quickly to 15.5% moisture.
Other environmental factors such as previous infected corn debris to provide fungal spores are important. Genetics of hybrids influence the vulnerability to silking and pollen timing problems when plants are under stress. Hybrids differ in kernel composition and development and spread of infection if fungi invade the ovules. Rapid drop in kernel moisture after black layer can be related to husk characters like thickness and looseness, essential to rapid loss of grain moisture in the field.
It is important to use care in analyzing cause if severe ear rot occurs. Was it the genetics of the environment that was primary?
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.