Some of the worst corn stalk and ear rot fungi live in your soils. Crop rotation is useful, but some pathogens that cause the most damage can still survive for several years. If you have been lucky enough to have heavy rains for a good harvest, there is a good chance that pathogens are “lurking in the bushes” waiting to attack your corn.
The disease triangle indicates that three elements must be present for a disease outbreak: a pathogen, a susceptible host culture, and an environment conducive to the spread of the pathogen. Foliar fungicides also appear to help reduce stem and ear rot. If the weather conditions are favorable for cultivation, they are also useful for pathogenic organisms.
Stem rots were responsible for some early loss of stem integrity in 2021. Stems in many fields failed the pinch or push test at an alarming rate, even in mid-September. Stress from dry weather may have contributed to this. Additionally, in fields where the corn initially lacked nutrients, plants may have cannibalized stems to fill the kernels.
Stem, ear rots
Anthracnose has become one of the major stem rot diseases. This pathogen attacks the roots and stems of plants already weakened by leaf diseases. The spores of this fungus can stay alive in the soil for a long time. This pathogen has been one of the biggest corn stalk killers in recent years. Anthracnose infects the stems when the spores splash from the soil to the lower internodes of the stems. It makes shiny black spots on the uppers that look like shoe polish. The stems turn black on the inside and may rot and drop.
Diplodia, Gibberella, and Fusarium stem rots are caused by fungi that can survive in the soil for many years. A pinkish color inside the stem pith may indicate stem rot by fusarium or gibberella. Dan Quinn, Purdue University Extension corn specialist, recently reported that in one field, even though tar spots were rampant, examining the pith indicated the presence of fusarium or gibberella. This is not yet confirmed.
Diplodies can infect the ears, usually starting at the base and extending throughout the ear. Infected grains have a low specific weight but are not known to produce toxins. Gibberella ear rot produces a pink fungus that usually begins at the tips of the ears. Fusarium causes a white to gray discoloration of seed groups or individual kernels scattered on the cob. There may also be a star pattern radiating from the point of attachment of the silk.
Gibberella and fusarium can produce mycotoxins. Infected grain should be tested before it is fed to livestock. Diplodies and Gibberellas can cause significant yield losses if corn is not harvested on time.
Aspergillus, another ear rot, is favored by hot, dry weather during grain filling. Symptoms are dusty, olive-green spore masses on the kernels. Aspergillus can produce aflatoxin, a potent mycotoxin that can cause docks or the discharge of corn to silos.
Check for ear and stalk rot in corn still in the field by removing the pods and pushing or pinching the stems. Right now, most corn will likely fail the pinch or push tests.
Nanda is Director of Genetics for Seed Genetics Direct, Jeffersonville, Ohio. E-mail [emailÂ protected] or dial 317-910-9876. If there is no response, please leave a message.