We humans are compelled to name what we see. This includes a guy like me whose PHD dissertation involved fungal taxonomy. And certainly it is important to distinguish among corn leaf diseases in order to identify how to defend against the disease in the future.
The fungi that show up on the stalks rotting late in the season, however, do not indicate the actual cause of the problem. The Diplodia, Colletotricum (anthracnose), Fusarium or Gibberella species that becomes the most obvious on the surface or inside the rotted stalk are quick invaders of dead or dying stalk tissue. Knowing the name may seem satisfying because it implies an aggressive pathogen attacking a helpless plant and thus the grower was not responsible. But, in a field or plot of single cross hybrids, all the plants are genetically identical. Surely these fungi are not only concentrated in a small area of the field where the rot occurred. The analysis should concentrate why those plants rotted and not the name of the fungus.
Late season stalk rot begins as a root rot. That occurs when the root tissue senesces because it no longer receives sufficient carbohydrate to maintain production of defense chemicals to fight off the many bacterial and fungi surrounding the roots. This caused the plant to wilt because of lack of water uptake. Wilting caused death of the stalk tissue and invasion by many fungi, the most evident being the Diplodia, Colletotrichum, Fusarium and Gibberella species. Usually there are other species also working on digesting the stalk tissue but weakness was greatly enhanced by simply the pith tissue wilting and therefore pulling away from the rind wall.
Although it may be satisfying to have a name for the most dominant fungus found on the dead stalk, a better analysis for reducing the problem in the future must include what triggered the root rot in the affected plants. Discussion of some of those factors is the topic of future blogs.
Visit us at the ASTA in Chicago, Dec 9-12 (booth G207)
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.