Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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August 23, 2008

August 23, 2008

Iowa State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246




Soybean Aphids


 Soybean aphid numbers have declined in most fields now and most soybean fields are at or near R6 (full seed size) when treating for soybean aphids is less likely to pay, so hopefully we are done with aphids for one more year.  Populations should be dropping soon in fields where the numbers are still high, as the winged aphids return to buckthorn plants to lay their eggs.


Bean Leaf Beetles


Bean leaf beetle numbers have been extremely low in fields that I have been in the last 2 weeks. The later planting of soybeans this year probably helped to keep beetle numbers low earlier in the season and itís possible that the recent wet weather may reduce the population of the 2nd generation beetles. Hopefully this is a pest we wonít have to deal with this  summer, but fields should continue to be scouted.


Northern Corn Rootworm Beetles


The most numerous insect pest (other than aphids) being found in most soybean fields again this summer is the northern corn rootworm beetle (greenish beetle about the size of bean leaf beetles). Fortunately the beetle seldom does enough leaf feeding in soybeans to cause economic problems, although they will feed on soybean leaves. It is another indication to me that we do have problems with this pest in rotated corn, since itís likely that this is where many of the beetles are coming from. Managing the problem on rotated corn will be discussed at the field day in Benton County on August 27 and the Fall Field Day at Crawfordsville on September 6. See below for details.




Sudden Death Syndrome


Soybean sudden death syndrome is more widespread than Iíve ever seen it in the past. I can find it in most soybean fields that Iíve been in, although in most cases it is in fairly small patches. It occurs most in areas where there has been some soil compaction, such as in end rows, or where the drainage is poor. The disease is caused by a soil borne fungus and the infection of the plants actually occurred early in the growing season. The disease is not actually spreading from plant to plant as it may appear as the patches become larger. Early planting in cool wet soils and flooding during the vegetative stages will increase the problems with this disease. Although early planting was not common this year, the excess rain that many areas of eastern Iowa received in May and June has likely increased the incidence of this disease. Usually soybean cyst nematode is also present in fields infested with sudden death syndrome. Planting varieties with soybean cyst nematode resistance as well as varieties that are more tolerant to sudden death can help reduce the problem. Also it is more likely to show up in the future where it has been seen in the past, so planting those fields last can also improve the chances of escaping the disease. For more information and a picture of the disease symptoms see my blog on the Iowa Farmer Today website at



Asian Soybean Rust


X.B. Yang now predicts that there is a greater than 50% chance that Iowa will see its first Asian soybean rust this year, but if it arrives it will be so late that it will have little to no affect on soybean production this year. It is beyond the time to spray for rust. Oklahoma is still the closest it has reached this summer. Visit the USDA Soybean Rust website for more updates.



Ear Twinning


            Virgil Schmitt has reported seeing some corn fields that are exhibiting double or multiple ears developing from one node. This is a phenomenon called ďtwinningĒ that was observed from Ohio to Iowa in 2006 and is showing up in these states again in 2007.  See the following article on the ISU Extension Agronomy webpage for more information and a picture:


Yield Estimates


            It is quite easy (if not always accurate) to estimate corn yields, since itís just a matter of counting kernels. Maybe the heat & humidity will drop one of these days so corn yield estimates can be taken without dieing from heat exhaustion. To estimate corn yields pull several ears of corn at random and count the number of rows of kernels and the number of kernels per row. Ignore kernels less than half size at the tip of the ear. Also measure off 1/1000 acre along one row in several places in the field and count the number of ears:

1/1000 acre =  26 ft 2Ē in 20Ē rows (or measure 13 ft 1Ē and count ears in 2 rows)

17 ft 5" in 30" rows
            14 ft 6" in 36" rows
            13 ft 9" in 38" rows

Number of kernels per 1/1000 acre = kernels per row X rows per ear X ears per 1/1000 acre.
Divide this number by about 90 to get bu/A (since there are about 90,000 kernels per bushel).




White Mold, Sudden Death, Rotation Resistant Rootworms & Fungicides on Corn

Discussed at Pest Management Tour on August 27 - 6:00 p.m.

Benton County

Corn and soybean disease management and managing rotation resistant rootworms will be featured at the Dean Folkmann farm just east of Newhall (just west of Linn Coop). X.B. Yang will discuss the results of a white mold fungicide trial on the farm and give a soybean rust update. Early observations about fungicides sprayed on corn this year will be discussed as well. Patti Prasifka, ISU Entomologist, will discuss the results of the rotation resistant rootworm monitoring that has been done in the area this year as well as management options for the problem. BASF and Linn Coop. will be providing a free meal and 6:00 p.m. followed by the tour. If you plan to attend, please call the Benton County extension office by Aug. 24 to help them with a meal count (319-472-4739).


Fall Field Day SE Iowa Research Farm  - Crawfordsville

September 6 - 1:30 p.m.

Topics will include grain storage issues, grain marketing, low linolenic soybeans and other alternative crop opportunities, and managing extended diapause northern corn rootworms.



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

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Last Update: August 23, 2007
Contact: Jim Fawcett

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