Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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July 19, 2012





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:   For example, just posted last Friday was a reminder about “Insurance Coverage for Drought-Damaged Crops” by William Edwards, Department of Economics.  i.e. Producers need to consult with their crop insurance agents before harvesting or destroying any drought-damaged crops.  See the article at:





With the lack of rain and extreme heat, it’s surprising so much of the corn crop still looks as good as it does. I’m seeing huge differences across the area, depending on both the amount of rain and soil type. Corn on the sands and poorer soils is close to death, with fields nearby on better soils still having very good yield potential, although rain will be needed soon to realize that potential. This year is also showing the advantage of having soybeans in the rotation, with corn on corn being hit especially hard and soybeans still having a chance for very good yields if rains return in August. It looks like pollination was good in most fields, which is amazing considering the 100+ temperatures that much of the corn was under during pollination. Now we’ll see how many of those kernels will make it into the bin and how many will abort. All of the eastern half to 2/3 of Iowa is now considered to be in a severe drought (


If Chopping Drought Stressed Corn:


1.    Test for nitrates.  Corn that is stunted and has no ears from drought is the most likely to have high nitrates, assuming normal nitrogen fertilization. The greatest risk is when the corn is green chopped and fed directly out of the field. Ensiling will take care of much of the nitrate problem. Leaving the lower 12-18” of the stalk in the field will reduce the problem since nitrates tend to concentrate in the lower stalk. A rain a few days before chopping tends to increase the problem. Before feeding send a sample to the lab to have it tested. A list of some forage testing labs can be found at If you go through your local vet, samples can be sent to the ISU Diagnostic Vet Lab (515-294-1950). Here’s a fact sheet on nitrate toxicity and testing:


2.    Test crop moisture for proper ensiling to insure good fermentation.  Good fermentation is important to reduce nitrate levels in the feed.  Don’t be fooled by how dry the drought damaged corn looks.  Most of the corn is still probably over 75% moisture.  Too wet to just ensile.


a.    To determine actual whole plant moisture:

1.            Sample some representative plants from the field.

2.            Chop the plants, maybe run them through a chipper-shredder or other devise.

3.            Test for moisture using the Koster moisture tester, or other method such as a microwave oven or heat lamp.  The microwave oven or heat lamp method is describe in:

4.            If the moisture is over 70%, the problem then becomes how to harvest and properly ensile this forage.  The answer is easy, but to accomplish this is difficult.  The answer is to add dry matter to reduce moisture content.  Air dry alfalfa or grass forage will decrease the moisture content of wet forage approximately 5 percentage units for each 150 to 200 pounds of material added per ton of wet forage weight.


The Value of Drought-Stressed Corn Silage


From the Drought Web Page, Dr. Edwards posted a news release titled “Pricing Drought Damaged Silage”.  This news release provides a simplified explanation of the value of this product.  However, within the news is a link to an Excel Spreadsheet that allows you to input your own specific factors to better price this product.  The news release is at:


Foliar Diseases


In general there has been less foliar diseases on corn this year, reducing the likelihood of a fungicide paying off. It is possible that a fungicide may improve the ability of the corn to tolerate the drought, but the results have been inconclusive on what little research has been done on the subject. We will certainly know more after this year, but hope we don’t need to use that knowledge for many years to come. Some have been reporting Goss’s Wilt showing up in some fields in the area again this year. Fungicides have no affect on bacterial diseases like Goss’s Wilt.


It was recently reported that southern rust was found in Butler and Grundy counties. Southern rust spreads much faster than common rust and thus is potentially much more damaging. Hot, humid conditions do favor southern rust development, and it is especially concerning that it has been found this early in the season. 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. Fungicides are effective on both species. For information on how to distinguish between the 2 diseases, see Allison Robertson’s article at


Spider Mites & Corn Aphids


Although more of a concern on soybeans, spider mites can damage corn as well, and some fields have already been sprayed in the area. If corn was sprayed with a synthetic pyrethroid earlier, it is more likely to have a spider mite problem now. Another pest usually associated with drought in corn is aphids. Some are reporting problems now. Fields need to be monitored for any pests that this unusual weather might be bringing on.




Spider Mites


Spider mite populations are increasing in the area, with some fields being sprayed already. The damage usually shows up on the edges of the fields first. Spider mite damage begins as little yellow dots or “stippling” on the lower leaves, and then leaves become entirely yellow and brown. Shake some leaves over a white piece of paper and look for little dots that move. A magnifying glass is useful to confirm you are looking at mites. There isn’t an exact threshold for the spider mites, but a general recommendation is to spray if mites are present on most plants and damage is found on the lower leaves. Sometimes just spraying the field edges is effective if the mites have not yet spread throughout the field, but if this is done its best to spray 100 feet or more beyond where the damage is seen. Many are spraying Lorsban or a Lorsban generic, although some are preferring to use a product containing bifenthrin (such as Brigade, Hero, or Cobalt), thinking the bifenthrin may have longer residual. DOW is recommending to use Lorsban at 1.5 pt/A to try to get better  residual. Use higher carrier volumes to try to improve the coverage. If weather conditions don’t change, more applications may be needed as more eggs hatch out. Most synthetic pyrethroids are not effective on spider mites, and can even increase problems by killing the predators of the mites. For more discussion see




Local Drought Meetings Will be Occurring over next 2-3 Weeks

See the ISU Drought Page for Details



If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: July 19, 2012
Contact: Jim Fawcett

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