Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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August 2, 2012

August 2, 2012




The drought continues to hang on.  The most recent outlook from the National Weather Service is that the drought will continue through harvest.  See  The August outlook is for above average temperatures and below average rainfall





Remember that ISU Extension is compiling resources on a web site to help you deal with the drought.  Resources on the web site are provided under various categories:  “Crops”, “Livestock”, “Dealing with Stress”, “Home and Yard”, “Financial Concerns”, and “Tips for Businesses”.  More information is being added daily.  Local educational events dealing with the drought can also be found on the page which is at


Along with the drought web page, stay tuned to articles posted on the ICM News:


And the ISU Extension Home Page also is focusing on drought issues





The University of Illinois is also gathering many drought resources, which are available at





And the University of Wisconsin is gathering many drought resources, which are available at





Remember to take care of yourself, your family, and your neighbors.  There is a great deal of stress, both financial and emotional, occurring.  No crop is worth more than you, your family members, or your neighbors.  The Iowa Concern Hotline is available 24-7-52 to help guide you through stressful times.  You can contact the hotline via phone (800-447-1985) or on-line chat at





If Chopping Drought Stressed Corn:


Remember to consider nitrate potential and to be sure the moisture content is correct.  Details were in the July 24, 2012 Crop Update




It is too early to tell if aflatoxin will be a problem or the extent of the problem because no aflatoxin has yet been produced.


Aflatoxin is produced by a yellow-green (olive green) mold called Aspergillus flavus.


Spores of Aspergillus flavus can enter the seed through silks when they are yellow-brown, which is shortly after pollination.  This is more likely to occur under drought conditions with temperatures above 90 degrees, and this has undoubtedly happened in at least some fields.


Once Aspergillus flavus has entered the seed, it must successfully colonize the seed.  The surface of the seed will be colonized first, but the surface colonization does not produce aflatoxin.  Aflatoxin is produced when the kernels become internally infected.  The kernel must be at about 32% moisture or less (down to about 16% moisture) for internal infection to occur; kernels are normally at 30 – 35% moisture at maturity.  As you scout corn fields as they approach black layer, pull back husks on several ears of each hybrid and look for signs of Aspergillus ear rot.  Most commonly, it will first show up on the kernels on the tip, especially if they have been damaged by insects or wild life.


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Early Kernel Colonization         Colonization of Ear Tip Kernels                 More Complete Colonization of the Ear

Pictures from Alison Robertson


Because Aspergillus flavus can produce aflatoxin in a temperature range of 52 – 104 degrees F. (optimum is 77 - 95 degrees) when the kernel moisture is about 16% up to about 30% (optimum is 18% - 20%), it is recommended that if more than 10% of the ears show signs of Aspergillus ear rot, the field should be harvested at 25 – 28% moisture and immediately dried to less than 15% moisture to minimize the opportunity for aflatoxin production.  When the weather is warm and the crop matures early, it is counter-intuitive to not take advantage of in-field drying, but allowing in-field drying when more than 10% of the ears show evidence of Aspergillus ear rot can quickly turn good corn into salvage corn.


If you suspect a potential aflatoxin issue, be sure to contact your crop insurance adjuster immediately.


Alison Robertson has a more complete discussion at



Foliar Diseases


Tom Hillyer has found southern corn rust in western Muscatine County. Southern corn rust spreads much faster than common rust and thus is potentially much more damaging. Hot, humid conditions favor southern rust development. If you find corn rust in your field, it is much more likely that it is common rust, and thus not as much of a concern. For information on how to distinguish between the 2 diseases, see Allison Robertson’s article at


Several of us have found Gray Leaf Spot in some corn fields.



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Gray Leaf Spot lesions on corn leaves (both pictures)


As most corn is in the late R3 stage of maturity or beyond, it is unlikely that a fungicide application for either disease would be profitable, but it is somewhat more likely to be profitable if southern corn rust is "exploding" in the field.





Two-Spotted Spider Mites


Two-spotted spider mites continue to be problematic in some soybean fields and are even in a few corn fields.  The University of Minnesota has just released three publications on two-spotted spider mite management that may be useful.  They are "Managing Two-Spotted Spdier Mites on Soybeans and Corn in Minnesota," "Managing Two-Spotted Spider Mites on Soybeans in Minneasota," and "Managing Two-Spotted Spider Mites on Corn in Minnesota." 





Drought Webinar

August 21, 2012, 1-3 p.m.


Watch for details and locations as they become available.



Local Drought Meetings will also be occurring over the next several weeks.


See the ISU Drought Page for Details:


Two that are not on the list at this writing will be conducted Friday, August 10, 2012:

Crop and livestock management issues and options along with an FSA update will be discussed at each.



If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: August 2, 2012
Contact: Virgil Schmitt

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