August 26, 2010
Top Leaf Death
During the last week many people have noted deterioration of upper leaves in the corn canopy. Often when the upper leaves of the corn plant die, top dieback caused by anthracnose is blamed, but there are other factors that can also cause the upper leaves to die. Northern corn leaf blight is very common this year. It also can cause the upper leaves to die. There have also been some reports of Goss’s Wilt in the area this year. Some environmental conditions, such as hot conditions during grain fill also can lead to the upper leaves dying. This was reported by Bob Nielson in Purdue at http://www.agry.purdue.edu/ext/corn/news/articles.05/TopLeafDeath-0828.html.
The bottom line, however, is that there is nothing that can be done at this time. Alison Robertson, ISU Extension Plant Pathologist, has written several articles that may help people differentiate between Goss’s wilt, anthracnose top dieback, and northern corn leaf blight in the field.
For differentiating between Goss’s 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 Goss’s 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 Goss’s wilt.
Arrested Ear Syndrome
There have been several reports of late applications of Ignite (glufosinate) and glyphosate on corn resulting in barren plants or unusual ear development on the plants. Ear development is stopped or arrested around silking time resulting in very small ears, similar to the baby ears served at salad bars. In some cases the plants turn red because of the lack of an ear to translocate the sugars to. Bob Nielson discovered a couple of years ago that applications of pesticides around V14 can cause this phenomenon. He concluded that it was the additives or surfactants in the formulation that was causing most of the problem. Even straight crop oil concentrate or non ionic surfactant applied a week or two before tasseling could cause the same problem. His report can be found at http://www.agry.purdue.edu/ext/corn/news/articles.08/ArrestedEars-1209.html.
Another ear deformity that is being found in some fields are “banana ears”, where there is poor pollination or kernel abortion on one side of the causing the ear to curve over like a banana. This symptom can be caused by nitrogen deficiency. If the leaves show severe N deficiency, some of the ears may show this problem.
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.
Sudden Death Syndrome
This will probably go down as the worst year ever for Sudden Death Syndrome (SDS). If you have to look to find it in your field, you are one of the lucky ones. Some fields are now totally dead from the disease. Fields with severe SDS most likely also have soybean cyst nematode (SCN). SCN symptoms are most likely to appear in dry years. I can’t remember the last dry year that we had, so it is easy to forget about SCN, but it is still there and contributes to SDS infection and severity. If you have not had your field tested for SCN, be sure to have some soil samples sent to a lab this fall. If SCN is present, start using nematode resistant soybeans in your rotation. This won’t solve the SDS problem, but can reduce the severity of the problem. More information on soil sampling for SCN can be found at http://www.extension.iastate.edu/CropNews/2008/1201tylka2.htm.
One good thing about this bad SDS year is it gives you a great opportunity to learn which soybean varieties are the most tolerant. Until someone comes up with a good seed treatment, variety selection is the best way to manage the disease. Take some good notes at any seed plots you look at in the next week or two.
FOR YOUR CALENDAR
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.
Nondiscrimination Statement and Information Disclosures