Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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July 17, 2008

August 21, 2008




Soybean Aphid


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Picture from Tom Hillyer
It appears that Soybean Aphid populations are continuing to increase in many fields.  The later planted fields and fields where a “preventive insecticide” (killing the beneficial insects) was included in the last herbicide application appear to be the fields most commonly over the threshold for Soybean Aphid.  Soybean aphids tend to not be as much of a problem in even-numbered years, but there are still some fields that need to be sprayed in those years, and, so far, it looks like 2008 will continue the pattern.  The economic threshold is 250 aphids per plant with 80% of the plants being infested and with populations increasing.  Once the soybeans reach growth stage R 5.5, an insecticide application is not needed.  If there is a seed 1/8 inch in diameter in a pod at one of the top two nodes with a fully expanded trifoliolate leaf on the main stem of the plant, the plant is about right at R 5.5.  Soybean aphid populations are declining in some fields, and if populations are declining or if the soybean aphids are preparing to leave the field, an insecticide application is not needed.  So, take note of the presence of winged aphids and alatoid nymphs (with wing pads), high predator activity, and/or diseased aphids as these are all signs that the population is in decline or will leave the field shortly. Scout these same fields again within a few days to note if populations are increasing or decreasing. 



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Winged Soybean Aphid
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Alatoid Soybean Aphid – Note the Wing (shoulder) Pads
An alternative for conventional scouting is to use the “speed scouting” method developed at the University of Minnesota. You only have to be able to count to 40 to use this method, but need to take a spreadsheet to the field to take notes and make a decision. You will most likely hit threshold with “speed scouting” before you actually hit the threshold using the conventional method.  The data suggests that if you hit the threshold using the “speed scouting” method, there is an 82 per cent chance you will soon go over the threshold using the conventional scouting method.  The following site describes the method and provides a link to download the spreadsheet.

Scouting techniques and management information can be found in SP 247, Soybean Aphids in Iowa – 2007, which can downloaded from





Japanese Beetles


Text Box:  I have been receiving many inquiries about when to expect feeding from Japanese Beetles to cease.   There is a single generation in the Midwest, with beetles living for 30 – 45 days. Beetle feeding tends to occur from late June to early September, with the heaviest defoliation in July and August.  With the generally cooler-than-normal weather, I would expect the beetles to live closer to 45 days than to 30 days.  The population of beetles in many soybean fields “exploded” about July 12 – 14, so adding 45 days to that would suggest feeding will continue for most of the rest of August.


In soybean, the economic threshold for the beetles is the general leaf defoliation threshold used for other pests. During the reproductive stages of soybeans, the threshold for considering an insecticide treatment is if greater than 20% of the leaf area is gone due to feeding. However, the high price of soybean may lower the threshold slightly.  But remember that most people tend to overestimate defoliation. If it looks like 20% defoliation, most likely it’s only 10%. The pictures in the following article can help in estimating percent defoliation:


For more information and insecticides labeled for Japanese beetles see the July 28, 2003 ICM Newsletter at


Soybean Sudden Death Syndrome


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                 Brown Stem Rot                                               Sudden Death Syndrome
Like 2007, Soybean Sudden Death Syndrome (SDS) is appearing in all of the counties I cover.  However, thus far in 2008, it appears to be less severe than in 2007.  Brown Stem Rot (BSR) can cause leaf symptoms identical to SDS.  See pages 70 – 72 of the March 26, 2007 Integrated Crop Management Newsletter or for identification and management of SDS and BSR.


If the field has not been tested for Soybean Cyst Nematode (SCN), the presence of SDS in the field should prompt a soil test for SCN as SCN is usually present if SDS is present.  The sample submission form and instructions for taking the sample are in PD-32 “Plant Nemnatode Sample Submission Form” which is available at Iowa State University Extension offices or can be downloaded from





Farm Progress Show

Tuesday, August 26 – Thursday, August 28, 2008


Stop at the Iowa State University Building


See for more details.



Annual Field Day

Northwestern Illinois Research and Demonstration Center – Monmouth, IL

8:00 a.m., Thursday, August 28, 2008

Program (Certified Crop Advisor Credits Available):



See for more details.



Fall Field Day

NE IA Research & Demonstration Farm – Nashua

1:30 p.m., Thursday, September 4, 2008


Program (Certified Crop Advisor Credits Available):


        Grain Market Outlooks - Dr. Hart, ISU Extension Economist     

        Considerations for fertilizing the 2009 crop - Dr. Sawyer, ISU Extension Soil Fertility Specialist     

        Corn & Soybean Growth and Development/Stage of Maturity Relative to Planting Date - Ken Pecinovsky, Farm Superintendant     

        Economics & Considerations of No-till & Tilled Systems - Andy Herringshaw, ISU Associate     

        Foliar Fungicide Application Decisions & Plant Disease ID - Dr. Mueller, ISU Extension Plant Pathologist


See for more details.


Fall Field Day

SE IA Research & Demonstration Farm – Crawfordsville

1:00 p.m., Wednesday, September 10, 2008


Tentative Program (check later for any  updates) (Certified Crop Advisor Credits Available):


        Farm and Season Update - Kevin Van Dee, Farm Superintendent, and Mark Carlton, ISU Extension Field Agronomist

        Grain Handling, Drying, and Storing – Shawn Shouse, ISU Extension Ag Engineer

        Farm Bill, Crop Financial Management in the Current Situation – Jim Jensen, ISU Extension Farm Management Specialist

        Weed Management - Mike Owen, ISU Extension Weeds Specialist


See for more details and any updates.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: August 21, 2008
Contact: Virgil Schmitt

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