I have gotten this question quite a few times the last few days, and have been noticing it in an increasing number of fields.

With all the rain, I haven’t had a chance to really good look at it, but did talk with one of our great ISU Extension Plant Pathologists, Alison Robertson. Here is a short version of what she shared with me, and she is planning an article addressing this issue in the next ISU Integrated Crop Management newsletter.

She cautioned me that “top dieback” isn’t always caused by anthracnose. In a 2005 article by Bob Nielsen of Purdue, he mentioned that top dieback can be from anthracnose, or other factors:

• It has been documented that due to certain weather conditions during grain fill, some hybrids can senesce from both the top and bottom of the plant- This “natural” pattern of upper leaf senescence usually affects all plants within a field or within areas of fields.
• Early death of top leaves can also be a result of severe drought stress. This is usually preceded by a gray-green color and wilting of the upper leaves. This drought-related pattern of upper leaf senescence often affects all plants within the drought-stressed areas of affected fields.
• Something we don’t see a lot of lately- corn borer damage can damage the upper stalk and cause it to wilt or “die back”. This will typically be random plants in the refuge areas. I haven’t noticed this type of dieback yet, but it could be there in some refuge areas.

Alison mentioned that she has noticed yellowing flag leaves of individual plants scattered in the field. She says that if you peel back the leaf sheaths you may see signs (pink sporulation) and symptoms (black lesions) on the stalk that can indicate anthracnose. Roger Elmore, ISU Extension Corn Specialist, Alison, myself and others have also noticed field borders, and some whole fields, with top dieback symptoms. We are all going to be taking a closer look as the weather improves to help determine what is causing the top dieback symptoms.

Check out Alison’s article in the Integrated Pest Management Newsletter, as I am pretty sure she will address what, if any, effect that the foliar fungicides applied to some of Iowa’s corn fields would have on the top dieback we are starting to see. I bet she’ll address yield impact and management issues as well.

SOURCE: ISU’s Clarke McGrath

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