Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


August 12, 2005

August 12, 2005



        Much of the area finally received a good rain, with more in the forecast, but unfortunately it has come too late to have a big impact on corn yields, although it should increase kernel size. August rains usually are very important for soybeans, so hopefully the rains came soon enough so we still have a shot at decent soybean yields. Most soybeans are between the R5 (beginning seed) and R6 (full seed) stage, so the rains will help the pods to fill out. Much of the corn is in the R4 (dough) stage, with some corn beginning to dent.



Two Spotted Spidermites


The rains and humid conditions, as well as break in the heat should help to reduce problems with this pest. For more information see the July 22, 2002 ICM Newsletter at and the July 18, 2005 article at


Soybean Aphids


Many fields have been sprayed for soybean aphids in the northern part of the area, although aphid populations have been considerably lower than what we saw in 2003. The rains should also help to reduce aphid numbers, and the aphid population should start to naturally decline in about a week. In many fields most of the aphids found recently have been the small off-white aphids, rather than the larger yellow-green aphids. It is the larger aphids that are the biggest threat to rapid reproduction resulting in soybean yield losses, although we should not ignore the small aphids in making treatment decisions. Hopefully spraying for soybean aphids is nearing an end for the season, but fields should continue to be scouted for another week or two for aphids. Treatment is recommended if aphid numbers are increasing and surpass 250 aphids/plant. For more information on soybean aphids see <> and the July 11, 2005  ICM Newsletter at

Asian Soybean Rust


There have been a few more confirmations of soybean rust in the far southern U.S., but no farther north than central Alabama, and no farther west than southern Mississippi. For the latest see



Watch for Corn Ear Rots This Fall


Some corn ears I pulled yesterday in Johnson County had a green mold growing on it that may be Aspergillus flavus, the fungus that can produce aflatoxin. The drought stress increases the likelihood that we will see more problems with the ear rots that produce mycotoxins this year. However, the presence of the fungus does not necessarily mean that the mycotoxin is present. For more information see the October 6, 2003 ICM Newsletter at




Late Summer Seeding of Forages


Now that we finally have received some rain, a late summer seeding of alfalfa may make sense for some producers if there is soil moisture to plant into. The target date to have forages seeded by for the best chance of establishment in the central third of Iowa is August 20. Since most common weeds don't germinate well this late in the season, we do not recommend a companion crop or pre-plant herbicide. For more information see the handout "Late Summer (Fall) Seeding of Forages in Iowa" or


Crawfordsville Fall Field Day - September 14 1:30 p.m.


The annual fall field day will be held at the SE Iowa Research Farm near Crawfordsville on September 14 at 1:30 p.m. Alison Robertson and X.B. Yang will be featured at the tour. They will present information from this year's fungicide trials and also will discuss alfatoxin and other mycotoxin concerns in corn. Mike Duffy, ISU Economist, will compare the economics of continuous versus rotated corn. Also featured will be Jim Jensen, on Low Sat And Low Lin Soybean Opportunities, and Kevin VanDee on Strip Intercropping.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: August 12, 2005
Contact: Jim Fawcett

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