August 23, 2010
Top Leaf Death
During the last week many people have noted deterioration of upper leaves in the corn canopy. Depending on the field, there often is more than one reason, some of which look very similar. The bottom line, however, is that there is nothing that can be done to slow down or stop any of them at this point in time.
The three diseases that I have run into that are easily confused are anthracnose top die-back, northern corn leaf blight, and Gosss wilt. Alison Robertson, ISU Extension Plant Pathologist, has written several articles that may help people differentiate between the diseases in the field.
For differentiating between Gosss wilt and northern corn leaf blight, see http://www.extension.iastate.edu/CropNews/2009/0731robertson.htm and http://www.extension.iastate.edu/CropNews/2008/0811robertsonjesse.htm.
For diagnosing anthracnose top die-back, see http://www.ipm.iastate.edu/ipm/icm/2007/9-10/topdieback.html. Both Gosss wilt and anthracnose leaf blight can have freckles. Look at the freckles under 20X or more magnification; if they are porcupine-like, it is anthracnose. If the lesions have a shine, like varnish, that is dried exudate or ooze from Gosss wilt.
Some people are also observing some ear rots. Alison also wrote an excellent article on differentiating between various ear rots and various stalk rots at http://www.extension.iastate.edu/CropNews/2009/1002robertson.htm.
FOR YOUR CALENDAR
Northeast Iowa Research and Demonstration Farm, Nashua
Fall Field Day on August 26, 2010, 1:00 p.m.
Details are posted at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.
Southeast Iowa Research and Demonstration Farm, Crawfordsville
September 15, 2010
10:30 a.m. Manure Injection Field Day
Noon Free Lunch
1:00 p.m. Regular Fall Field Day
Details are posted at http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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